Digital Notes

COURSE MATERIAL
III Year B. Tech II- Semester
(2023-2024)
MECHANICAL ENGINEERING

UNCONVENTIONAL MACHINING
PROCESS
R20A0323

Prepared by:
Dr. K. Chandra Sekhar, Associate Professor

MALLA REDDY COLLEGE OF ENGINEERING & TECHNOLOGY

DEPARTMENT OF MECHANICAL ENGINEERING
(Autonomous Institution-UGC, Govt. of India)
Secunderabad-500100,Telangana State, India.
www.mrcet.ac.in
MALLA REDDY COLLEGE OF ENGINEERING & TECHNOLOGY
(Autonomous Institution – UGC, Govt. of India)
DEPARTMENT OF MECHANICAL ENGINEERING

CONTENTS

1. Vision, Mission & Quality Policy

2. Pos, PSOs & PEOs

3. Blooms Taxonomy

4. Course Syllabus

5. Lecture Notes (Unit wise)

a. Objectives and outcomes

b. Notes

c. Presentation Material (PPT Slides/ Videos)

d. Industry applications relevant to the concepts covered

e. Question Bank for Assignments

f. Tutorial Questions

6. Previous Question Papers

www.mrcet.ac.in
MALLA REDDY COLLEGE OF ENGINEERING & TECHNOLOGY
(Autonomous Institution – UGC, Govt. of India)

VISION
❖ To establish a pedestal for the integral innovation, team spirit, originality and
competence in the students, expose them to face the global challenges and become
technology leaders of Indian vision of modern society.

MISSION
❖ To become a model institution in the fields of Engineering, Technology and
Management.
❖ To impart holistic education to the students to render them as industry ready
engineers.
❖ To ensure synchronization of MRCET ideologies with challenging demands of
International Pioneering Organizations.

QUALITY POLICY

❖ To implement best practices in Teaching and Learning process for both UG and PG
courses meticulously.

❖ To provide state of art infrastructure and expertise to impart quality education.

❖ To groom the students to become intellectually creative and professionally

competitive.
❖ To channelize the activities and tune them in heights of commitment and sincerity,
the requisites to claim the never - ending ladder of SUCCESS year after year.

For more information: www.mrcet.ac.in

MALLA REDDY COLLEGE OF ENGINEERING & TECHNOLOGY
(Autonomous Institution – UGC, Govt. of India)
www.mrcet.ac.in
Department of Mechanical Engineering

VISION

To become an innovative knowledge center in mechanical engineering through state-of-

the-art teaching-learning and research practices, promoting creative thinking professionals.

MISSION

The Department of Mechanical Engineering is dedicated for transforming the students into
highly competent Mechanical engineers to meet the needs of the industry, in a changing
and challenging technical environment, by strongly focusing in the fundamentals of
engineering sciences for achieving excellent results in their professional pursuits.

Quality Policy

✓ To pursuit global Standards of excellence in all our endeavors namely teaching,

research and continuing education and to remain accountable in our core and
support functions, through processes of self-evaluation and continuous
improvement.

✓ To create a midst of excellence for imparting state of art education, industry-

oriented training research in the field of technical education.
MALLA REDDY COLLEGE OF ENGINEERING & TECHNOLOGY
(Autonomous Institution – UGC, Govt. of India)
www.mrcet.ac.in
Department of Mechanical Engineering
PROGRAM OUTCOMES
Engineering Graduates will be able to:
1. Engineering knowledge: Apply the knowledge of mathematics, science, engineering
fundamentals, and an engineering specialization to the solution of complex engineering
problems.
2. Problem analysis: Identify, formulate, review research literature, and analyze complex
engineering problems reaching substantiated conclusions using first principles of
mathematics, natural sciences, and engineering sciences.
3. Design/development of solutions: Design solutions for complex engineering problems
and design system components or processes that meet the specified needs with appropriate
consideration for the public health and safety, and the cultural, societal, and environmental
considerations.
4. Conduct investigations of complex problems: Use research-based knowledge and
research methods including design of experiments, analysis and interpretation of data, and
synthesis of the information to provide valid conclusions.
5. Modern tool usage: Create, select, and apply appropriate techniques, resources, and
modern engineering and IT tools including prediction and modeling to complex engineering
activities with an understanding of the limitations.
6. The engineer and society: Apply reasoning informed by the contextual knowledge to
assess societal, health, safety, legal and cultural issues and the consequent responsibilities
relevant to the professional engineering practice.
7. Environment and sustainability: Understand the impact of the professional engineering
solutions in societal and environmental contexts, and demonstrate the knowledge of, and
need for sustainable development.
8. Ethics: Apply ethical principles and commit to professional ethics and responsibilities and
norms of the engineering practice.
9. Individual and teamwork: Function effectively as an individual, and as a member or
leader in diverse teams, and in multidisciplinary settings.
10.Communication: Communicate effectively on complex engineering activities with the
engineering community and with society at large, such as, being able to comprehend and
write effective reports and design documentation, make effective presentations, and give
and receive clear instructions.
11.Project management and finance: Demonstrate knowledge and understanding of the
engineering and management principles and apply these to one’s own work, as a member
and leader in a team, to manage projects and in multidisciplinary environments.
MALLA REDDY COLLEGE OF ENGINEERING & TECHNOLOGY
(Autonomous Institution – UGC, Govt. of India)
www.mrcet.ac.in
Department of Mechanical Engineering
12.Life-long learning: Recognize the need for and have the preparation and ability to engage
in independent and life-long learning in the broadest context of technological change.

PROGRAM SPECIFIC OUTCOMES (PSOs)

PSO1 Ability to analyze, design and develop Mechanical systems to solve the
Engineering problems by integrating thermal, design and manufacturing Domains.

PSO2 Ability to succeed in competitive examinations or to pursue higher studies or

research.

PSO3 Ability to apply the learned Mechanical Engineering knowledge for the
Development of society and self.

Program Educational Objectives (PEOs)

The Program Educational Objectives of the program offered by the department are broadly listed
below:

PEO1: PREPARATION

To provide sound foundation in mathematical, scientific and engineering fundamentals necessary

to analyze, formulate and solve engineering problems.

PEO2: CORE COMPETANCE

To provide thorough knowledge in Mechanical Engineering subjects including theoretical

knowledge and practical training for preparing physical models pertaining to Thermodynamics,
Hydraulics, Heat and Mass Transfer, Dynamics of Machinery, Jet Propulsion, Automobile
Engineering, Element Analysis, Production Technology, Mechatronics etc.

PEO3: INVENTION, INNOVATION AND CREATIVITY

To make the students to design, experiment, analyze, interpret in the core field with the help of
other inter disciplinary concepts wherever applicable.

PEO4: CAREER DEVELOPMENT

To inculcate the habit of lifelong learning for career development through successful completion
of advanced degrees, professional development courses, industrial training etc.
MALLA REDDY COLLEGE OF ENGINEERING & TECHNOLOGY
(Autonomous Institution – UGC, Govt. of India)
www.mrcet.ac.in
Department of Mechanical Engineering

PEO5: PROFESSIONALISM

To impart technical knowledge, ethical values for professional development of the student to solve
complex problems and to work in multi-disciplinary ambience, whose solutions lead to significant
societal benefits.
MALLA REDDY COLLEGE OF ENGINEERING & TECHNOLOGY
(Autonomous Institution – UGC, Govt. of India)
www.mrcet.ac.in
Department of Mechanical Engineering

Blooms Taxonomy
Bloom’s Taxonomy is a classification of the different objectives and skills that educators set for
their students (learning objectives). The terminology has been updated to include the following
six levels of learning. These 6 levels can be used to structure the learning objectives, lessons,
and assessments of a course.

1. Remembering: Retrieving, recognizing, and recalling relevant knowledge from long‐ term
memory.
2. Understanding: Constructing meaning from oral, written, and graphic messages through
interpreting, exemplifying, classifying, summarizing, inferring, comparing, and explaining.
3. Applying: Carrying out or using a procedure for executing or implementing.
4. Analyzing: Breaking material into constituent parts, determining how the parts relate to
one another and to an overall structure or purpose through differentiating, organizing, and
attributing.
5. Evaluating: Making judgments based on criteria and standard through checking and
critiquing.
6. Creating: Putting elements together to form a coherent or functional whole; reorganizing
elements into a new pattern or structure through generating, planning, or producing.
MALLA REDDY COLLEGE OF ENGINEERING &
TECHNOLOGY
(Autonomous Institution – UGC, Govt. of India)
www.mrcet.ac.in
Department of Mechanical Engineering
B. Tech (ME) R-20

MALLA REDDY COLLEGE OF ENGINEERING AND TECHNOLOGY

III Year B.Tech. ME- II Sem L/T/P/C
3/-/-/3

(R20A0323) UNCONVETIONAL MACHINING PROCESSES

(Professional Elective III)
Course Objectives:

1. To understand the need and importance of nontraditional machining methods.

2. To know the basic principle, equipment, process variables and mechanics of
metal removal in abrasive jet machining and water jet machining.
3. To study the fundamentals of tool design, surface finishing and metal removal
rate of electro chemical grinding, electro chemical machining and electro
chemical honing.
4. To understand principles of operation, types of electrodes and process
parameters and machine tool selection in EDM and Electric discharge grinding
and wire cut process.
5. To know the basics of Electron Beam Machining and comparison of thermal and
non-thermal processes.
UNIT I: INTRODUCTION AND MECHANICAL ENERGY BASED PROCESSES
Unconventional machining Process – Need – classification – merits, demerits and
applications. Abrasive Jet Machining – Water Jet Machining – Abrasive Water Jet Machining
- Ultrasonic Machining. (AJM, WJM, AWJM and USM). Working Principles – equipment used
– Process parameters – MRR- Applications.

UNIT II: THERMAL AND ELECTRICAL ENERGY BASED PROCESSES

Electric Discharge Machining (EDM) – Wire cut EDM – Working Principle-equipments-

Process Parameters-Surface Finish and MRR- electrode / Tool – Power and control Circuits-
Tool Wear – Dielectric – Flushing –– Applications. Laser Beam machining and drilling, (LBM),
plasma, Arc machining (PAM) Principles – Equipment –Types - Beam control techniques –
Applications.

UNIT III: CHEMICAL AND ELECTRO-CHEMICAL ENERGY BASED PROCESSES

Chemical machining and Electro-Chemical machining (CHM and ECM)- Etchants – Maskant -
techniques of applying maskants - Process Parameters – Surface finish and MRR-
Applications. Principles of ECM- equipments-Surface Roughness and MRR Electrical circuit-
Process Parameters- ECG and ECH - Applications.

UNIT IV: ADVANCED NANO FINISHING PROCESSES

Abrasive flow machining, chemo-mechanical polishing, magnetic abrasive finishing, magneto

rheological finishing, magneto rheological abrasive flow finishing their working principles,
equipments, effect of process parameters, applications, advantages and limitations.

Malla Reddy College of Engineering and Technology (MRCET)

B. Tech (ME) R-20

UNIT V: RECENT TRENDS IN NON-TRADITIONAL MACHINING PROCESSES

Recent developments in non-traditional machining processes, their working principles,

equipments, effect of process parameters, applications, advantages and limitations.
Comparison of Traditional and non-traditional machining processes.

Course Out comes:

1. Understand the knowledge on need for unconventional machining process and can
perform experiments on USM process and are able to apply these concepts in academic
research.

2. Learn the working of AJM, WAJM and WJM, can perform experiments on those processes
and are able to apply these concepts in academic research.

3. Understand the fundamental concepts of CM, ECM, EDM process and can perform
experiments on those processes and are able to apply these concepts in academic research.

4. Selection of machining process for various work materials

5. Apply suitable machining process for the typical component.

TEXT BOOK:

1.Advanced machining processes - VK Jain, Allied publishers.

2.Modern Machining Process - Pandey P.C. and Shah H.S., TMH.

REFERENCES:

1.New Technology - Bhattacharya A, The Institution of Engineers, India 1984.

2.Unconventional Machining Processes - C. Elanchezhian,B. Vijaya Ramnath and M Vijayan,
Anuradha Publications, 2005.
3. Unconventional Manufacturing Processes – M.K. Singh, New Age International Publishers.

Malla Reddy College of Engineering and Technology (MRCET)

 Phase Diagrams

Syllabus : Unconventional machining Process - Need - classification - merits, demerits

and applications. Abrasive Jet Machining - Water Jet Machining - Abrasive Water Jet
Machining - Ultrasonic Machining. (AJM, WJM, AWJM and USM). Working Principles -
equipment used - Process parameters - MRR- Applications.

Section No. Topic Name Page No.

1.1 Introduction 1-2

1.2 Comparison between Conventional and Unconventional 1-4

Machining Processes

1.3 Classification of Advanced Machining Processes 1-5

1.4 Classification of Unconventional Machining Process 1-8

1.5 Physical Parameters of the Process 1 - 11

1.6 Hybrid Process 1 - 15

1.7 General Characteristics of Unconventional Machining 1 - 16

Process

1.8 Comparison of Various Unconventional Machining Process 1 - 18

1.9 Mechanical Energy Based Process 1 - 19

1.10 Abrasive Jet Machining (AJM) 1 - 19

1.11 Abrasive Water Jet Machining (AWJM) 1 - 30

1.12 Water Jet Machining (WJM) 1 - 40

1.13 Ultra-Sonic Machining 1 - 48

1.14 Two Marks Questions with Answers (Part - A) 1 - 64

1.15 Long Answered Questions (Part - B) 1 - 68

1.16 Multiple Choice Questions with Answers 1 - 70

1-1 Unconventional Machining Processes

1-1 Unconventional Machining Processes
1.1 Introduction
 The main work of an engineer and scientist is the development of newer methods.
 The main ideas behind such works are :
o Economic considerations.
o Replacement of old manufacturing methods by faster ones and more efficient ones.
o To get high accuracy and high surface finish.
o Use low cost material instead of costlier ones.
o Developing new methods of machining to machine hard materials which cannot be
machined by conventional or normal methods, like tungsten, uranium, tantalum
stainless steel, etc.
 The use of such costly and hard to machine materials is common in tool design industries,
aircraft industries, space research equipments, power plants, ammunition industries, etc.
 To meet the requirements of these industries newer methods are developed by the engineers
and scientists.
 These machining methods are called as “Non-conventional or Un-conventional or Non-
traditional or Modern methods of machining”.
 The common parameters to be taken into consideration for selecting a particular process are
as follows :
o Physical properties of work material.
o Type of operation to be performed like cutting, hole making, etc.
o Shape and size required to be produced.
o Process capabilities i.e. expected tolerance, power requirement, Metal Removal Rate
(MRR), surface finish, etc.
o Economy of the process.
o Physical properties of workpiece material.

Limitations of conventional manufacturing process

i) Conventional manufacturing process are difficult to machine the harder or newly
developed materials like carbides, ceramics, High Strength Temperature Resistance
(HSTR) alloys etc.,
ii) The surface finish level is not quite high.
iii) High tolerance or close tolerance cannot be achieved.
iv) Difficult to obtain complex shapes.
 v) Automated data transmission is not possible.
vi) Mass production at high production rate with high accuracy is not possible.
vii) The generation of shallow holes, non-circular micro sized holes are not possible.
viii) High wastage of material.
ix) The degree of accuracy and precision are not in best position.
x) A large number of holes in a single workpiece with better quality is quite difficult.
xi) Unconventional machining process not so effective on soft materials like aluminium
because accuracy cannot be maintained due to more material removal rate.

1.1.1 Characteristics of Non Conventional Processes

Non Traditional Machining (NTM) processes are characterized as follows :

 Material removal may occur with chip formation or even no chip formation may take place.
For example in AJM, chips are of microscopic size and in case of Electrochemical
machining material removal occurs due to electrochemical dissolution at atomic level
 In NTM, there may not be a physical tool present. For example in laser jet machining,
machining is carried out by laser beam. However in Electrochemical Machining there is a
physical tool that is very much required for machining
 In NTM, the tool need not be harder than the work piece material. For example, in EDM,
copper is used as the tool material to machine hardened steels.
 Mostly NTM processes do not necessarily use mechanical energy to provide material
removal. They use different energy domains to provide machining. For example, in USM,
AJM, WJM mechanical energy is used to machine material, whereas in ECM
electrochemical dissolution constitutes material removal.Comparatively high initial cost.

1.1.2 Need for Development of Un-Conventional Processes

 The strength of steel alloys has increased five folds due to continuous R and D effort.
 In aero-space requirement of high strength at elevated temperature with light weight led to
development and use of hard titanium alloys, nimonic alloys, and other HSTR alloys. .
 The ultimate tensile strength has been improved by as much as 20 times.
 Development of cutting tools which has hardness of 80 to 85 HRC which cannot be
machined economically in conventional methods led to development of non –traditional
machining methods.
 1. Technologically advanced industries like aerospace, nuclear power, ,wafer fabrication,
automobiles has ever increasing use of High –strength temperature resistant (HSTR)
alloys (having high strength to weight ratio) and other difficult to machine materials like
titanium, SST,nimonics, ceramics and semiconductors. It is no longer possible to use
conventional process to machine these alloys.
2. Production and processing parts of complicated shapes (in HSTR and other hard to
machine alloys) is difficult , time consuming an uneconomical by conventional methods
of machining.
3. Innovative geometric design of products and components made of new exotic materials
with desired tolerance , surface finish cannot be produced economically by conventional
machining.
4. The following examples are provided where NTM processes are preferred over the
conventional machining process :
o Intricate shaped blind hole – e.g. square hole of 15 mm  15 mm with a depth of
30 mm with a tolerance of ± 100 microns.
o Difficult to machine material – e.g. Inconel, ti-alloys or carbides, ceramics,
composites , HSTR alloys, satellites etc.,
o Low stress grinding – Electrochemical grinding is preferred as compared to
conventional grinding.
o Deep hole with small hole diameter – e.g. φ 1.5 mm hole with l/d = 20
o Machining of composites.
Definition :
A machining process is called non-traditional if its material removal mechanism is
basically different than those in the traditional processes, i.e. a different form of energy (other
than the excessive forces exercised by a tool, which is in physical contact with the work piece)
is applied to remove the excess material from the work surface, or to separate the workpiece
into smaller parts.

1.2 Comparison between Conventional and Unconventional

Machining Processes
S.No Conventional Process Un Conventional Process

1. The cutting tool and work piece are There is no physical contact between the tool
always in physical contact with relative and work piece, In some nontraditional process
motion with each other, which results in tool wear exists.
friction and tool wear.
 2. Material removal rate is limited by NTM can machine difficult to cut and hard to
mechanical properties of work material. cut materials like titanium, ceramics,
nimonics, SST, composites, semiconducting
materials.

3. Relative motion between the tool and Many NTM are capable of producing complex
work is typically rotary or reciprocating. 3D shapes and cavities.
Thus the shape of work is limited to
circular or flat shapes. In spite of CNC
systems, production of 3D surfaces is still
a difficult task.

4. Machining of small cavities , slits , blind Machining of small cavities, slits and
holes or through holes are difficult. Production of non-circular, micro sized, large
aspect ratio, shall entry angle holes are easy
using NTM.

5. Use relative simple and inexpensive Nontraditional processes requires expensive

machinery and readily available cutting tools and equipment as well as skilled labour,
tools. which increase the production cost
significantly.

6. Capital cost and maintenance cost is low. Capital cost and maintenance cost is
high.

7. Traditional processes are well established Mechanics of Material removal of Some of

and physics of process is well understood. NTM process are still under research.

8. Conventional process mostly uses Most NTM uses energy in direct form For
mechanical energy. example : laser, Electron beam in its direct
forms are used in LBM and EBM respectively.

9. Surface finish and tolerances are limited High surface finish(up to 0.1 micron) and
by machining inaccuracies. tolerances (25 Microns)can be achieved.

10. High metal removal rate. Low material removal rate.

1.3 Classification of Advanced Machining Processes

The different non-conventional machining methods are generally classified using the
following criteria :
(1) According to the type of energy used : Mechanical, electro-chemical or electrothermal,
chemical, etc.
(2) According to the energy source : Pneumatic or hydraulic pressure, mechanical pressure,
high current or voltage, etc.
(3) According to the medium for energy transfer : High velocity particles, physical contact,
electrolyte, hot gases, electrons, radiation, etc.
(4) According to the metal removal mechanism : Erosion, spark erosion, shear,
vaporisation, etc.

1.3.1 Process Selection

The common parameters to be taken into consideration for selecting a particular process are
as follows :

(i) Physical parameters of unconventional machining methods

Table 1.1 : Physical parameters in non-conventional machining methods

Unconventional machining methods

Parameters
EDM EBM PAM LBM USM AJM ECM

100 to 3 3
Voltage (Vts) 15010 100 4.510 220 220 10 to 30
300

Current
50 0.001 500 2 12 1 10,000
(Amp)

Power (kW) 2.7 0.15 50 - 2.4 0.22 100

Gap (mm) 0.025 100 7.5 150 0.25 0.75 0.2

Abrassive
Dielectric Hydrogen Abrasive
Medium Vacuum Air in water or Electrolyte
fluid or argon in gas
paraffin
(ii) Shape and size required to be produced
 The different non-conventional machining methods have some special shape producing
capability as follows :
o Standard hole drilling : EDM and USM
o Fine hole drilling and contour machining : ECM
o Clean, rapid cuts and profiles : PAM
o Micro-machining and drilling : LBM and EBM

(iii) Process capability

 Out of all the non-conventional machining methods, EDM has the lowest specific power
requirement and it can achieve sufficient accuracy whereas ECM has the highest MRR
(Metal Removal Rate).
 USM and AJM have low MRR and combined with tool wear whereas LBM and EBM
have high penetration rates with low MRR.

(iv) Process economy

 The process economy of various non-conventional machining methods is given in the
following Table 1.2.
Table 1.2 : Process economy

Process Capital cost Power Efficiency

requirement

EDM Medium Low High

EBM High Low Very high

PAM Very low Very low Very low

LBM Medium Very Low Very high

USM Low Low High

AJM Very low Low High

ECM Very high Medium Low

Conventional Low Low Very low

method
(v) Physical properties of workpiece material

(vi) Type of operation to be performed

1.3.2 Commonly Used Advanced Machining Processes

(1) Electro-Discharge Machining (EDM)
(2) Wire-cut Electro-Discharge Machining (W-EDM)
(3) Electron Beam Machining (EBM)

(4) Plasma Arc Machining (PAM)

(5) Laser Beam Machining (LBM)
(6) Ultra Sonic Machining (USM)

(7) Abrasive Jet Machining (AJM)

(8) Electro-Chemical Machining (ECM)
(9) Chemical Machining (CM)

(10) Electro-Chemical Grinding (ECG)

(11) Water-Jet Machining (WJM)
(12) Ion-Beam Machining (IBM)

1.4 Classification of Unconventional Machining Process

Unconventional machining process are classified as follows :
a) Based on the type of energy required to shape the material
i. Thermal energy method
ii. Electrical energy method
iii. Electro Chemical energy method
iv. Chemical energy method
v. Mechanical energy method.
Table 1.3 : Classification of non-conventional processes
 b) Based on the mechanism involved in the process
i. Erosion
ii. Ionic dissolution
iii. Vaporisation
c) Source of energy required for material removal
i. Hydrostatic pressure
ii. High current density
iii. High voltage
iv. Ionised material
d) Medium of transfer of energies
i. High voltage particles
ii. Electrolyte
iii. Electron
iv. Hot gases

Abreviations Used :
1. AJM - Abrasive Jet Machining
2. USM - Ultrasonic Machining
3. WJM - Water Jet Machining
4. AWJM - Abrasive Water Jet Machining
5. ECM - Electro Chemical Machining
6. ECG - Electro Chemical Grinding
7. EJD - Electro Jet Drilling
8. EDM - Electro Discharge Machining
9. LJM - Laser Jet Machining
10. EBM - Electron beam Machining
11. PAM - Plasma Arc Machining
12. CHM - Chemical Milling
13. PCM - Photo Chemical Milling
1.4.1 Selection of Process
The correct selection of the non-traditional machining methods must be based on the
following aspects.
i) Physical parameters of the process
ii) Shape to be machined
iii) Process capability
iv) Economics of the processes

1.5 Physical Parameters of the Process

EBM and LBM require high voltages and require careful handling of equipment. EDM and
USM require medium power. EBM can be used in vacuum and PAM uses oxygen and hydrogen
gas.
Parameters Non Traditional Process

USM AJM CHM ECM EDM EBM LBM PAM

Potential 220 220 - 10-30 100-300 150 kV 4.5 kV 100

(Volts)

Current 12 1 - 10000 50 0.001 2 500

(Amps)

Power 2.4 0.22 - 100 2.70 0.15 - 50

(KW)

Gap (mm) 0.25 0.75 - 0.20 0.025 100 150 7.5

Medium Abrasives Abrasive Liquid Electrolyte Dielectric Vacuum Air Argon

In water In gas chemical Oil H2/O2

1.5.1 Shapes Cutting Capablity

The different shapes can be machined by NTM. EBM and LBM are used for micro drilling
and cutting. USM and EDM are useful for cavity sinking and standard hole drilling. ECM is
useful for fine hole drilling and contour machining. PAM can be used for cutting and AJM is
useful for shallow pocketing.
 Application Process well suited
Producing micro holes LBM
Producing small holes EBM
For deep holes (L/D >20) and
ECM
contour machining
For shallow holes USM and EDM
For precision through cavities in
USM and EDM
workpieces
For Honing ECM
For etching small portions ECM and EDM
For grinding AJM and EDM
For deburring USM and AJM
For threading EDM
For clean, rapid cuts and profiles PAM
For shallow pocketing AJM

Capability to shape
Capability to

Contou
ring a Micro Pocketing
Drill Cavity sinking Through
surface Drill Operation cutting
Process
Accurate Standard Deep Deep
L/D L/D Operation Operation Shallow pocketing Shallow cutting
<20 >20 Pocketing cutting

USM P - G P G G P P P -

AJM - - F P P F - - G -

ECM G - G G F G G G G G

CHM - F - - P F G P G -

EDM F - G F G G G G P -

EBM - F F P P P - - G F

LBM - G F P P P - - G F

PAM - - F - P P - - G G

P - Poor , F- Fair, G- Good

1.5.2 Process Capability
The process capability of NTM which achieves higher accuracy has the lowest specific
power requirement. ECM can machine faster and has a low thermal surface damage depth.
USM and AJM have very material removal rates combined with high tool wear and are used
nonmetal cutting. LBM and EBM are, due to their high penetration depth can be used for
micro drilling, sheet cutting and welding. CHM is used for manufacture of PCM and other
shallow components.
Material Surface Accuracy Specific power
Removal rate finish
Process
Accurate Standard
L/D <20 L/D >20 Operation Operation

USM P - G P G G

AJM - - F P P F

ECM G - G G F G

CHM - F - - P F

EDM F - G F G G

EBM - F F P P P

LBM - G F P P P

PAM - - F - P P

1.5.3 Applicability to Material

Metals and alloys Non-Metals
Aluminum Steel Super Titanium Refractory Ceramics Plastics Glass
Process Alloys Material

USM P F P F G G F G

AJM F F G F G G F G

ECM F G G F F - - -

CHM G G F F P P P P

EDM F G G G G - - -

EBM F F F F G G F F
 LBM F F F F P G F F

PAM G G G F P - P -

P - Poor , F- Fair, G- Good

1.5.4 Machining Characteristics

Process A B C D E

USM 300 7.5 0.2-0.5 25 2,400

AJM 0.8 50 0.5-1.2 2.5 250

ECM 15,000 50 0.1-2.5 5 1 Lakh

CHM 15 50 0.5-2.5 5 -

EDM 800 15 0.2-1.2 125 2700

EBM 1.6 25 0.5-2.5 250 150(Avg)

2 (Peak)
LBM 0.1 25 0.5-1.2 125 2 (Avg.)
200 (Peak)
PAM 75,000 125 Rough 500 50,000

3
A – Metal Removal rate obtained (in mm /min)
B – Tolerance maintained (in micron)
C – Surface finish obtained (in micron)
D – Depth of surface damaged (in micron)
E – Power required for machining (in watts)
1.5.5 Effects on Equipment and Cooling
Process Tool wear ratio Machining Safety Toxity
medium contamination

USM 10 B A A

AJM - B B B

ECM - C B A
 CHM - C B A

EDM 6.6 B B B

EBM - B B A

LBM - A B A

PAM - A A A

A - No Problem , B - Normal Problem, C - Critical Problem

Volume of work material removed
Tool wear ratio =
Volume of tool electrode removed
1.6 Hybrid Process
 To increase the capabilities of the machining processes, two or more than two machining
processes are combined to take advantage of each and every processes.
 For example : A conventional grinding produces good surface finish and low tolerances but
the components are associated with burrs, heat affected zone and residual stresses. But,
electrochemically machined components do not have such defects. Hence, a hybrid process
known as electrochemically grinding (ECG) has been developed.
 Similarly, other hybrid processes like electrochemical spark machining, electrochemical arc
machining, electro-discharge abrasive, etc. have been developed.
 This chapter includes the following processes :
i) Abrasive Flow Finishing (AFF)
ii) Magnetic Abrasive Finishing (MAF)
iii) Abrasive Water Jet Machining (AWJM)
iv) Wire Electric Discharge Machining (W - EDM)
v) Electrochemical Grinding (ECG)
vi) Electrochemical De-burring (ECD)
vii) Shaped Tube Electrolytic Machining (STEM)
viii) Electrolyte Jet Machining (EJM)
ix) Electrolytic in-Process Dressing (ELPD)
x) Ultrasonic assisted EDM (U - EDM)
xi) Rotary EDM
xii) Electrochemical Discharge Machining (ECDM)
xiii) Laser surfac
1.7 General Characteristics of Unconventional Machining Process
Process Characteristics Process Parameters,
Typical MRR or cutting speed

Chemical 0.025 - 0.1 mm/min

 Shallow removal (upto 12 mm) on
Machining (CHM)
large flat or curved surfaces;
 Blanking of thin sheets;
 Low tooling and equipment cost;
 Suitable for low production runs.
Electrochemical Voltage – 5 to 25
 Complex shapes with deep cavities; 2
Machining DC- 1.5 to 8 A/mm
(ECM)  High MRR; 2.5 – 12 mm/min Depending
 Expensive tooling and equipment; on current density

 High power consumption;

 Medium to high production quantity.
Electrochemical 2
 Cutting off and sharpening hard A: 1-3 A/mm
Grinding 3
(ECG) materials such as tungsten carbide tools; Typically 1500 mm /
min per 1000 A
 Also used as a honing process;
 Higher material removal rate than
grinding.

Electrical V: 50-380
Discharge  Shaping and cutting complex parts made
A : 0.1-500
Machining (EDM) of hard materials; Typically
3
 Some surface damage may result; 300 mm /min.
 Also used for cutting and grinding;
 Versatile expensive tooling and
equipment;
Wire EDM Varies with
 Contour cutting of flat or curved
workpiece material and its
surfaces; thickness.
 Expensive equipment.
Laser Beam 0.5 – 7.5 m/min
 Cutting and hole making in thin
Machining
(LBM) materials
 Heat Affected Zone (HAZ)’
 Does not require vacuum
 Expensive equipment
 Consumes much energy
 Extreme caution required in use
Abrasive Water Jet Upto 7.5 m/min.
 Single and multilayer cutting f metallic
Machining
(AWJM) and non- metallic materials
Electron Beam 3
 Cutting and hole making on thin 1-2 mm /min.
Machining
(EBM) materials
 Very small holes and slots.
 HAZ
 Requires vacuum
 Expensive equipment
Water Jet Varies considerably
 Cutting all types of non-metallic
Machining with workpiece material.
(WJM) materials to 25 mm. and greater in
thickness.
 Suitable for contour cutting of flexible
materials
 No thermal damage
 Environmentally safe process.
Abrasive Jet Varies considerably with
 Cutting, slotting, deburring, flash
Machining workpiece material.
(AJM) removal, etching and cleaning of metallic
and non-metallic materials.
 Tends to round off sharp edges
 Some hazard because of airborne
particulates. (Airborne particulate matter,
which includes dust, dirt, soot, smoke,
and liquid droplets emitted into the air, is
small enough to be suspended in the
atmosphere)
1.8 Comparison of Various Unconventional Machining Process
Process
S.No EDM ECM EBM LBM PAM USM AJM WJM
parameters
1 Metal By using Based on By using By using high Heating, Slurry of By using By
Removal powerful faraday’s high intensity of melting and small abrasive high stream using high
Technique electric spark Laws of velocity laser beam vaporizing particles is of abrasive velocity of
electrolysis beam of by using forced against particles water jet
electrons plasma workpiece by mixed with
means of air
vibrating tool

2 Work Electrically Difficult to All All materials All Tungsten Hard and Soft
material conductive machine materials except those materials Carbide, brittle and non-
metals and Electrically having high which Glass, Quartz, materials like metallic
alloys conductive thermal conduct ceramics, etc, glass, quartz, materi
materials conductivity electricity ceramics, etc als like
and high wood,
reflectivity plastic,
paper-
board etc
3 Tool material Copper, Copper, Electron Laser Beam Plasma Low Abrasives Water
yellow, alloy brass, Beam carbon steel, like jet
of zinc, titanium, stainless steels aluminium
copper, copper oxide, silicon
tungsten etc., tungsten, carbide, glass
stainless powder etc.,
steel etc.,

4 Metal
removal 15 to 80 27 15 to 40 0.10 2500 14 0.014 0.6
(mm3 / sec)
5 Surface
0.5 to
finish 0.25 0.2 to 0.8 0.4 to 6 0.4 to 6 Rough 0.2 to 0.7 0.5 to 1.2
0.8
in μm
6 Power
requirement Low Medium Low Very low Very low Low Low High
7 Capital cost Medium High High High Low High Very low High
8 Efficiency High Low Very high Very high Very low High High
High
9 Applications Production of Machining Micro Drilling Profile Efficiently Intricate Machining
complicated hard machining micro holes cutting of applied to hole shapes non-
and irregular materials operations (upto stainless machine glass, in hard and metallic
shaped and complex on thin 250 μm) and steel, ceramics, brittle materials
profiles and shaped parts materials cutting very monel and tungsten etc., materials
re sharpening like narrow slots super alloy
of cutting drilling, plates
tools slotting,
scribing etc.,
10 Limitations Not suitable Not suitable Not Taper of Low Low metal Low MRR, Difficult
for non- for non- suitable for 0.05 mm accuracy removal rate, low to
conducting conducting large work when work high rate of accuracy machine
materials materials pieces, thickness is tool wear hard
necessity more than materials
of vacuum 0.25 mm
1.9 Mechanical Energy Based Process
The mechanical energy based processes are as follows :
Abrasive Jet Machining
Water Jet Machining
Abrasive Water Jet Machining

1.10 Abrasive Jet Machining (AJM)

 AJM uses a stream of fine grained abrasives (of size 10 to 40 microns) mixed with air or
some other carrier gas at high pressure.
 This stream is directed on the work surface by using a suitable nozzle.
 The velocity of carrier gas or air is upto 200 to 400 m/sec.
 Due to this high speed, impact on the work surface erosion takes place by abrasive particles
and metal removes from the workpiece.
 AJM differs from the conventional sand blasting process in the way that the abrasive is
much finer and the effective control over the process parameters and cutting action. This
process is chiefly employed to cut hard and brittle materials which are thin, sensitive to heat
and have a tendency to break away or chip off easily.

Construction
 Fig. 1.1 shows typical setup for Abrasive Jet Machining, which consists of a ‘mixing
chamber’ in which fine grained abrasive particles are filled through a holding device like a
‘hopper’.
 This mixing chamber vibrates (upto 50 cycles/sec) and amplitude of these vibrations
controls the flow of abrasive particles. To control the amplitude of vibration, regulator is
placed in the system.
 Compressed air or high pressure gas is supplied to the mixing chamber through a pipe line,
which carries a pressure gauge to control its pressure.
 These particles mix in the stream of gas, travel via a hose and pass through a nozzle. This
stream of mixture of gas and abrasive particles is called as Abrasive Jet.

Process
 In abrasive jet machining abrasive particles are made to impinge on work material at high
velocity. Jet of abrasive particles is carried by carrier gas or air.
 The high velocity stream of abrasives is generated by converting pressure energy of carrier
gas or air to its Kinetic energy and hence high velocity jet.
 Fig. 1.1

 Nozzles directs abrasive jet in a controlled manner onto work material.

 The high velocity abrasive particles remove the material by micro-cutting action as well as
brittle fracture of the work material.

Working

Fig. 1.2 Schematic diagram of AJM

 Through hopper, fine grained abrasive powder is filled in a mixing chamber.
 The gas or air is supplied under pressure into the chamber; the pressure of gas varies from 2
to 8 kg/cm2.
 The gas is supplied through the pipeline which carries a pressure gauge and regulator to
control the flow.
 This mixture of high pressure gas and compressed air is passed through a nozzle on the the
surface of workpiece, and due to high speed mixture erosion is caused and metal removal
takes place.

Equipment :
Abrasive jet machining consists of

1. Gas propulsion system 2. Abrasive feeder

3. Machining chamber 4. AJM nozzle
5. Abrasives

1. Gas Propulsion System

 It supplies clean and dry air. Air, nitrogen and carbon dioxide to propel the abrasive
particles. Gas may be supplied either from a compressor or a cylinder.
 In case of a compressor, air filter cum drier should be used to avoid water or oil
contamination of abrasive powder. Gas should be non-toxic, cheap, easily available.
 It should not excessively spread when discharged from nozzle into atmosphere.
 The propellant consumption is of order of 0.008 m3/min at a nozzle pressure of 5 bar
and abrasive flow rate varies from 2 to 4 gm/min for fine machining and 10 to 20 gm/min
for cutting operation.

2. Abrasive Feeder
 Required quantity of abrasive particles is supplied by abrasive feeder. The filleted
propellant is fed into the mixing chamber where in abrasive particles are fed through a
sieve.
 The sieve is made to vibrate at 50-60 Hz and mixing ratio is controlled by the
amplitude of vibration of sieve.
 The particles are propelled by carrier gas to a mixing chamber.
 Air abrasive mixture moves further to nozzle. The nozzle imparts high velocity to
mixture which is directed at work piece surface.
 Fig. 1.3

3. Machining chamber
 It is well closed so that concentration of abrasive particles around the working chamber
does not reach to the harmful limits. Machining chamber is equipped with vacuum dust
collector.
  Special consideration should be given to dust collection system if the toxic material (like
beryllium) are being machined.

4. AJM nozzle
 AJM nozzle is usually made of tungsten carbide or sapphire ( usually life – 300 hours
for sapphire, 20 to 30 hours for WC) which has resistance to wear.
 The nozzle is made of either circular or rectangular cross section and head can be head
can be straight, or at a right angle.
 It is so designed that loss of pressure due to the bends, friction etc is minimum possible.
 With increase in wear of a nozzle, the divergence of jet stream increases resulting in
more stray cutting and high inaccuracy.

Fig. 1.4

Nozzle material Round shape nozzle Rectangular shape slot Life of nozzle,
diameter, mm dimension, mm hours

Tungstern carbide (WC) 0.2 to 1.0 0.075  0.5 to 0.15  2.5 12 to 30

Sapphire 0.2 to 0.8 –– 300

5. Abrasives
 Aluminum oxide (Al2O3) Silicon carbide (SiC) Glass beads, crushed glass and sodium
bicarbonate are some of abrasives used in AJM. Selection of abrasives depends on MRR ,
type of work material, machining accuracy.
 Abrasives Grain Sizes Application
Aluminum oxide(Al2O3) 12, 20, 50 microns Good for cleaning, cutting
and deburring
Silicon carbide (SiC) 25,40 micron Used for similar
application but for hard material
Glass beads 0.635 to 1.27 mm Gives matte finish

Dolomite 200 mesh Etching and polishing

Sodium bi carbonate 27 micros Cleaning, deburring and
cutting of soft material Light
finishing below 50 C

1.10.1 Mechanism of Material Removal in AJM

Fig. 1.5 Mechanism of metal removal in abrasive jet machining

When the abrasive particles impinge on the work piece or work surface at a high velocity,
the impact of the particles causes brittle fracture at the places where the particles hit and the
following gas or air varies away the dislodges small workpiece particles.(wear partilces). The
mathematical model of the material removal rate is based on the following assumptions.
1. The abrasive particles are considered to be rigid and spherical bodies of equal diameter
to the average grit size.
2. The material removed is equal to the volume of indentation in the case of a ductile
work material. It is equal to the chord length of indentation and is hemispherical in shape
in the case of brittle material.
3/2 1/4 3/4
MRR for brittle material = 1.04[ MV /ρ H ]
2
MRR for ductile material = 0.5[MV /H]
Where, M = The abrasive mass flow rate
V = The impact velocity
ρ = The density of the particle
H = The material hardness of the work piece.
 From the equation, Velocity plays a dominant role compared to the mass flow rate on MRR.
Under low velocity conditions ductile materials show lower MRR.
 For successful utilization of AJM process, it is necessary to analyze the following process
criteria.
1. Material removal rate
2. Geometry and surface finish of work piece
3. Wear rate of the nozzle
However, process criteria are generally influenced by the process parameters as enumerated
below :

 Abrasives
a) Material – Al2O3, SiC, glass beads, crushed glass, sodium bi carbonate
b) shape – irregular/regular
c) Size – 10 to 50 microns
d) Mass flow – 2-20 gm/min

 Carrier Gas 3
a) Composition – Air, CO , N
2 2 b) Density - 1.3 kg/m
c) Velocity - 500 to 700 m/s d) Pressure - 2 to 10 bar
e) Flow rate - 5 to 30 microns

 Abrasive Jet
a) Velocity - 100 to 300 m/s
b) Mixing ratio – Volume flow rate of abrasives/Volume flow rate of gas c) Stand off
distance – SOD - 0.5 to 15 mm.
d) Impingement angle – 60 to 90 deg.

 Nozzle
a) Material – WC/Sapphire
b) Diameter – 0.2 to 0.8 mm
c) Life – 300 hours for sapphire, 20 to 30 hours for WC

Process capability 3
1.
Material removal rate – 0.015 cm /min
2. Narrow slots – 0.12 to 0.25 mm ± 0.12 mm
3. Surface finish -0.25 micron to 1.25 micron
4. Sharp radius up to 0.2 mm is possible
 5. Steel up to 1.5 mm, Glass up to 6.3 mm is possible to cut
6. Machining of thin sectioned hard and brittle materials is possible.

1.10.2 Parameters in AJM

The parameters which affect MRR and accuracy of the machining process are :

1. Carrier gas :
 A carrier gas used in the process must not flare excessively when discharged from the
nozzle into the atmosphere. A gas used should be non-toxic, cheap, easily available and
capable of being dried easily.
 Commonly used gases are air, nitrogen and carbon di-oxide.
 If an air compressor is used proper line filters must be fixed to avoid water or oil
contamination of the abrasive powders. Since these contamination presents clogging
problem in the nozzle.
 Oxygen should never be used due to hazardous problem.

Fig. 1.6

2. Types of abrasives :
 The abrasive used in the process should have a sharp and irregular shape and should
have excellent flow characteristic.
 Commonly used abrasives are aluminium oxide and silicon carbide for general
machining and grooving whereas sodium bi-carbonate for fine finishing and dolomite
for etching and light cleaning purpose.
 Reuse of abrasives is not recommended since the cutting ability of abrasive decrease
after the usage and also the contamination of wear materials clogging the nozzle and the
cutting unit orifices.
 It is important to note that sodium bicarbonate is hygroscopic and will absorb
moisture if heated above 49° thus rendering it useless, if allowed to become moist.

3. Jet velocity :
 The kinetic velocity of the abrasive jet is utilised for metal removal by erosion.
  The velocity is a function of nozzle pressure, nozzle design and abrasive grain size.
 Higher nozzle pressure results in greater MRR. Also, higher grain size produces higher
MRR. The inside diameter of the nozzle is about 0.04 mm.

Fig. 1.7

4. Stand - Off Distance (SOD) or Nozzle Tip Distance (NTD) :

 It is the distance between the face of the nozzle and working surface of the workpiece to
be machined.
 Generally, it is kept about 0.7 mm to 1.0 mm.
 The shape and size of cavity produced as well as the surface of the workpiece is affected
by NTD.
 If NTD increases the velocity of abrasive particles striking on the workpiece also
increases, hence MRR also increases.
 Initially MRR increases with NTD after which it remains unchanged for a certain NTD
and then falls gradually. Fig. 1.8 shows effect of NTD on MRR

Fig. 1.8

5. Size of the abrasive grain

 The MRR in the AJM process depends on the size of the abrasive grain.
 The abrasives are available in many sizes ranging from 10μ to 50 μ. But best cutting
results have been obtained if the size of the bulk ranges from 15 μ to 40 μ
  Finer grains are less irregular in shape and possess lesser cutting ability. They are used
for polishing, fine deburring and cleaning operations.
 Too fine powder may tend to cake in the abrasive storage tank and hence reduce the
rate of flow and affects the MRR.
 Over size particles also affect the MRR by plugging the orifice and reduce the velocity
of the jet by means of its weight.
 Coarse grains are normally recommended for cutting and peening operations.

6. Effect of mixing ratio on MRR

Fig. 1.9

 Increased mass flow rate of abrasive will result in a decreased velocity of fluid and will
thereby decreases the available energy for erosion and ultimately the MRR.
 It is convenient to explain to this fact by term MIXING RATIO. Which is defined as
Volume flow rate of abrasives per unit time
Mixing ratio (M) =
Volume flow rate of carrier gas per unit time
The effect of mixing ratio on the material removal rate is shown above.
 A large value of M results in higher rate of material removal up to a certain limit and
then it gets reduced because a large abrasive flow rate decreases the jet velocity which is
responsible for causing the impact of the abrasive on to the work piece material.
 Also it presents the problem of clogging the nozzle. Thus for a given condition there is
an optimum mixing ratio that results in a maximum MRR. But when the abrasive mass
flow rate increases the MRR also increases.

7. Work Piece Material

 The AJM process is best suited for machining hard, brittle and heat sensitive metals,
alloys and non-metallic materials like Quartz, Germanium, Silicon, Glass, Ceramics,
Mica and refractory materials of thin sections.
8. Shape of Cut
 It is not possible to machine or cut parts with sharp corners because of stray cutting.

9. Nozzle Design
 The nozzle has to withstand the corrosive action of abrasive particles and must be made
of material which offers high resistance to wear.
 The nozzle is normally made of tungsten carbide or sapphire.
 The life of the nozzle is ascertain. A tungsten carbide nozzle lasts between 12 hours and
30 hours.
 A sapphire nozzle lasts around 300 hrs. Operation when used with in 27 m abrasive
powder.
 Nozzles are made with an external taper to minimize the secondary effects.

10. Accuracy and surface finish

 The control of the various parameters results in a tolerance in the region of ±0.05 mm
 Normal production using AJM technique ends up in an accuracy of ±0.1 mm
 The corner radius obtained can be limited to 0.1 mm.
 Taper is around 0.05 mm per 10 mm penetration.
 Slots as narrow as 0.12 to 0.25 mm can be produced.
 The surface finish ranges from 0.4 to 1.2 mm in most of the applications.

Advantages of AJM

 Brittle materials of thin sections can be easily machined.

 No direct contact between the tool and workpiece, hence less damage to the workpiece
surface.
 Holes of any shape and intricate cavities can be machined.
 Initial investment is low as compared to other methods.

 Power consumption is low.

Disadvantages of AJM
 AJM is suitable only for brittle materials, as MRR is high for brittle materials.
 Machining accuracy obtained is poor i.e. upto ± 50 microns.
3
 MRR is low i.e. upto 0.05 cm /hr.
  There is always a chance of abrasive particles getting inserted in the work material,
hence cleaning needs to be done after machining.
 The used abrasive powder can not be reused.
 Process tends to pollute the environment.

Applications of AJM
 The process is best suited for machining brittle and heat sensitive materials like glass,
quartz, sapphire, ceramics, etc.
 It is used for drilling holes, cutting slots, cleaning hard surfaces, deburring, polishing,
etc.
 It is used for producing high quality surface.
 It is used for reproducting designs on a glass surface with the help of masks made of
rubber, copper, etc.
 Used for etching markings on glass cylinders.
 Used for frosting interior surfaces of glass tubes.
 Used for cutting thin sectioned fragile components made of glass, refractories, ceramics,
mica, etc.
 Used for aperture drilling for electronic microscopes

1.10.3 Metal Removal Rate (MRR) in AJM

 The material removal rate in abrasive set machining is given by,
3    3
M.R.R. = K  N  d3  v    … (1.1)
2 12H 2
where, K = Constant
N = Number of abrasive particles impacting per unit time.
d = Mean diameter of abrasive particles.
v = Abrasive particles velocity
ρ = Density of abrasive particle
H = Hardness of work material

1.11 Abrasive Water Jet Machining (AWJM)

History
 Dr. Franz in 1950’s first studied UHP (Ultra High –Pressure) water cutting for forestry
and wood cutting (pure WJ) 1979 Dr. Mohamed Hashish added abrasive particles to
 increase cutting force and ability to cut hard materials including steel, glass and concrete
(abrasive WJ)
 First commercial use was in automotive industry to cut glass in 1983
 Soon after, adopted by aerospace industry for cutting high-strength materials like
Inconel, stainless steel and titanium as well as composites like carbon fiber.
 We know that, Abrasive Jet Machining (AJM), Abrasive Flow Finishing (AFF) and
Ultrasonic Machining (USM) are the processes which make use of abrasives for
machining of materials.
 In case of AJM, air driven abrasive jet strikes the workpiece and removes the material
whereas in USM abrasive grains in liquid slurry strike the liquid surface and cut the
material at low MRR.
 Now - a - days a hybrid process called abrasive Water Jet Machining or Cutting (AWJM
or AWJC) is used which makes use of abrasives with water jet for machining.
 This process is similar to AJM except that, in this case water is used as a carrier fluid
instead of gas.
 This process is mainly suitable for electrically non -conductive and difficult to machine
materials more rapidly and efficiently than the other processes.
Definition
 Abrasive water jet machining is a mechanical energy based material removal process in
which abrasives are mixed with water to form the abrasive slurry.
 It is a material removal process where the material is removed or machined by the
impact erosion of the high velocity stream of water and abrasive mixture which is
focused on to the work piece.
 This process is similar to abrasive jet machining except that the water is used as a carrier
medium instead of dry air.

Working Principle
 During the process, a jet of water and a stream of abrasives coming from two different
directions, mix up and flows through the abrasive jet nozzle. Refer Fig. 1.10.
 Because of nozzle, velocity of the abrasive rises rapidly.
 Thus, a high velocity stream of mixture of abrasives and water impinges on the surface
of workpiece and removes material.
 According to the material of workpiece, the removal of material may occur due to
erosion, shear or due to rapidly change in localized stress fields.
  This process is used for cutting, drilling and cleaning of hard materials. It is capable to
cut ceramics, composites, rocks, metals, etc.
 The pressure at which water jet operates is about 400 MPa and jet velocity is about
900 m/s.
 The commonly used abrasives in this process are silica, garnet and silicon carbide. For
hard materials, hard type of abrasive is used.

Fig. 1.10 : Working principle of AWJM

 The set-up of AWJM consists of four important elements as follows :

i) Pumping System ii) Abrasive Feed System
iii) Abrasive Water Jet Nozzle iv) Catcher

i) Pumping system
 It produces high velocity water jet by pressurizing water with the help of intensifier.
 For this purpose a high pressure motor is also required.
ii) Abrasive feed system
 This system delivers a controlled flow of abrasive particles to the jet nozzle. It delivers a
stream of dry abrasives to the nozzle.
 The flow of water jet in a mixing chamber or tube is responsible to create enough
suction for the flow of the abrasives.
 The rate of flow of abrasives can be adjusted by changing the size of the control orifice.

iii) Abrasive water jet nozzle

 This nozzle performs mixing of abrasive jet and water, and forms a high velocity water
abrasive jet.
 It gives a coherent and focused abrasive stream at exit of nozzle. This nozzle is made of
hard materials like sapphire, tungsten carbide or boron carbide.
 The abrasive water jet nozzle may be single jet side feed type or multiple jet central feed
type. Refer Fig. 1.11.

Fig. 1.11 Abrasive water jet nozzle

  In a single jet side feed nozzle, the abrasives fed from the side and mix with water jet in
the mixing chamber. These nozzles are less costly, simple but less efficient.
 In a multiple jet central feed nozzle, a centrally located abrasive feed system is
surrounded by multiple water jets. It gives higher nozzle life and better mixing of
abrasives and water jet.

iv) Catcher
 Catcher is a long narrow tube placed under the point of cut to capture the used jet.
 It is used when the nozzle is stationary and the workpiece moves.
 When the workpiece is stationary and the nozzle moves, water filled settling tank is
provided below the workpiece.
 “Catcher” is used to absorb the residual energy of the AWJ and dissipate the same.
 Figure shows three different types of catcher – water basin type, submerged steel balls
and TiB2 plate type.

Fig. 1.12

1.11.1 Types of AWM

AWJ are mainly of two types,
i) Entrained type ii) Suspended type
 Fig. 1.13

Fig. 1.14

 In entrained type AWJM, the abrasive particles are allowed to entrain in water jet to form
abrasive water jet with significant velocity of 800 m/s. Such high velocity abrasive jet can
machine almost any material.
 In suspension AWJM the abrasive water jet is formed quite differently. There are three
different types of suspension AWJ formed by direct, indirect and Bypass pumping method.
1.11.2 Process Variables
The process variables in AWJM are as follows :
 Flow rate and pressure of water
 Type, size and flow rate of abrasives
 Water nozzle and abrasive jet nozzle design
 Feed rate and stand - off distance
 Material of workpiece
 Number of passes
 Mixing tube dimensions (length, diameter and cutting angle)

1) Pressure of the water

 Pc is the minimum critical pressure required to cut the material.
 A minimum critical pressure Pc exits because of the minimum abrasive particle velocity
 required to cut specific materials.
 The value of Pc for mild steel is between 20.7 and 27.5 MPa.

Fig. 1.15
2) Water flow rate
 Fig. 1.15 shows the depth of cut is affected by varying the water flow rate (increasing
the nozzle diameter) while maintaining the constant pressure.
 As the flow rate increases, the slope of the curve decreases because the saturation point
is reached.
 As the nozzle diameter increases and the water flow rate increases, the rate of increase
in the particle velocity is reduced, thus reducing the depth of cut.
3) Abrasive flow rate
 Abrasive flow rate versus depth of cut is a linear relationship up to a point
 Above a critical flow rate, the cutting efficiency decreases.
 This is because of the fact that, as the abrasive flow rate increases (with a fixed water
flow rate), particle velocity begins to decrease faster than the rate at which the number
of abrasive particle impacts increase.

4) Abrasive particle size

 The most common abrasive particle sizes used for AWJM range from 100 to 150 grit
 An optimum abrasive particle size also exists for each particular nozzle mixing chamber
configuration.

5) Abrasive type
 The type of abrasive used is also an important parameter.
 Garnet, silica and silicon carbide are the most commonly used abrasives.
 Selection of abrasive type is usually determined by the hardness of the material that is
being cut.

6) Traverse rate
 When traverse rates are increased the depth of cut decreases.
 There is also a minimum critical traverse rate below which further increases in depth of
cut are not obtained.
 If the traverse rate is not maintained at a relatively uniform velocity, a rough edge will
result because of the nature of the process.

Fig. 1.16 Depth of cut Vs traverse rate

7) Stand-off-distance

Fig. 1.17 Stand off distance

 Data generated by some researchers indicate that depth of cut is approximately linear
relative to SOD. Increasing SOD decreasing the depth of cut.
 When mixing is efficient and process parameters are correct, a deviation in SOD of up
to ±12.7 mm can be tolerated without degradation of the cut quality.
 If SODs are increased to a distances of about 80mm, the process will no longer cut but
will efficiently clean and de-scale surfaces.

1.11.3 Process Capabilities

 AWJM can be thought of as a combination of WJM and AJM principles.
 But in terms of capability, AWJM combines the best of both processes, resulting in a new
process that can cut materials whether they are hard or soft at high rates and in very thick
sections.
 AWJM can cut materials as thick as 200mm and still maintain a comparatively narrow kerf.
 Kerf width is a function of the material thickness and usually is between 1.5 and 2.3 mm.
 The resulting taper on the cut edge is a function of the material hardness,
 Where hard materials have the widest kerf at the top of the cut and soft materials have the
widest kerf at the bottom of the cut.

Advantages
 It can cut electrically non - conductive and hard materials rapidly and efficiently.
 Cutting speed is high.
 The process has multi-direction cutting capacity.
 No fire hazards and no dust problem.
 High quality of machined surface is obtained.
 Recycling of abrasive particles is possible.
 The process requires low power.
 During the process, no thermal or distortion stresses.
 Make all sorts of shapes with only one tool.
 No heat generated.
 Unlike machining or grinding, waterjet cutting does not produce any dust or particles
that are harmful if inhaled.
 The kerf width in waterjet cutting is very small, and very little material is wasted.
 Waterjet cutting can be easily used to produce prototype parts very efficiently. An
operator can program the dimensions of the part into the control station, and the waterjet
will cut the part out exactly as programmed. This is much faster and cheaper than
drawing detailed prints of a part and then having a machinist cut the part out.
 Waterjets are much lighter than equivalent laser cutters, and when mounted on an
automated robot. This reduces the problems of accelerating and decelerating the robot
head, as well as taking less energy.

Disadvantages
 This process can cut limited number of materials economically. During the cutting of
tool steel and other hard materials, the cutting rate it low hence it require more time.
This increases the cost of machining.
 Very thick parts with good dimensional accuracy cannot be cut by this process.
 Taper is also a problem with waterjet cutting in very thick materials. Taper is when the
jet exits the part at a different angle than it enters the part, and can cause dimensional
inaccuracy. Decreasing the speed of the head may reduce this, although it can still be a
problem.
Applications
 This process is suitable for cutting of metals (copper, lead, tungsten, copper alloys,
aluminium, tungsten carbide, etc.) and non - metals (graphite, silica, glass, concrete,
acrylic, etc.).
 It is used to machine the sandwiched honeycomb structural material used in the
aerospace industries.
 It is used for cutting materials in a number of industries like aerospace, oil, foundry,
automotive, construction and glass.
 Different types of steels can be cut into different shapes like plate, tube, corrugated
structure, etc.

1.12 Water Jet Machining (WJM)

Definition :
In this process high pressure and high velocity stream of water is used to cut the relatively
softs and non-metallic materials like paper boards, wood, plastics, rubber, fibre glass, leather
etc.,

Introduction
 Key element in WJM is a jet of water.
 Water jet travels at velocities as high as 900 m/s.
 When the water stream strikes a work piece surface, the erosive force of water removes
the material rapidly.
 The water, in this case, acts like a saw and cuts a narrow groove in the work piece
material.
 True cold cutting process – no HAZ (Heat Affected Zones), mechanical stresses or
operator and environmental hazards

Principle
 The water jet machining involves directing a high pressure (150-1000 MPa) high
velocity (540-1400 m/s) water jet (faster than the speed of sound) to the surface to be
machined.
 The fluid flow rate is typically from 0.5 to 2.5 ltr/min
 The kinetic energy of water jet after striking the work surface is reduced to zero.
 The bulk of kinetic energy of jet is converted into pressure energy.
  If the local pressure caused by the water jet exceeds the strength of the surface being
machined, the material from the surface gets eroded and a cavity is thus formed.
 Water is the most common fluid used, but additives such as alcohols, oil products and
glycerol are added when they can be dissolved in water to improve the fluid
characteristics.

Equipment
Typical work materials involve soft metals, paper, cloth, wood, leather, rubber, plastics,
and frozen food. If the work material is brittle it will fracture, if it is ductile, it will cut well.
Water jet machining consists of :

1. Hydraulic pump 2. Intensifier 3. Accumulator

4. High pressure tubing 5. Jet Cutting nozzle 6. Catcher

1. Hydraulic pump
 Powered from a 30 kilowatt (kW) electric motor
 Supplies oil at pressures as high as 117 bars.
 Compressed oil drives a reciprocating plunger pump termed an intensifier.
 The hydraulic pump offers complete flexibility for water jet cutting and cleaning
applications.
 It also supports single or multiple cutting stations for increased machining productivity.

Fig. 1.18
2. Intensifier
 Accepts the water at low pressure (typically 4 bar) and expels it, through an
accumulator, at higher pressures of 3800 bar.
 The intensifier converts the energy from the low-pressure hydraulic fluid into ultra high
pressure water.
 The hydraulic system provides fluid power to a reciprocating piston in the intensifier
center section.
 A limit switch, located at each end of the piston travel, signals the electronic controls to
shift the directional control valve and reverses the piston direction.
 The intensifier assembly, with a plunger on each side of the piston, generates pressure in
both directions.
 As one side of the intensifier is in the inlet stroke, the opposite side is generating ultra
high pressure output.
 During the plunger inlet stroke, filtered water enters the high-pressure cylinder through
the check value assembly.
 After the plunger reverses direction, the water is compressed and exits at ultrahigh
pressure.

3. Accumulator
 Maintains the continuous flow of the high-pressure water and eliminates pressure
fluctuations.
 It relies on the compressibility of water (12 percent at 3800 bar) in order to maintain a
uniform discharge pressure and water jet velocity, when the intensifier piston changes
its direction.

4. High pressure tubing

 Transports pressurized water to the cutting head.
 Typical tube diameters are 6 to 14 mm.
 The equipment allows for flexible movement of the cutting head.
 The cutting action is controlled either manually or through a remote-control valve
specially designed for this purpose.
5. Jet cutting nozzle
 Nozzle provides a coherent water jet stream for optimum cutting of low-density, soft
material that is considered unmachinable by conventional methods.
 Nozzles are normally made from synthetic sapphire.
 About 200 h of operation are expected from a nozzle, which becomes damaged by
particles of dirt and the accumulation of mineral deposits on the orifice due to erosive
water hardness.
 A longer nozzle life can be obtained through multistage filtration, which removes
undesired solids of size greater than 0.45 μm.
 The compact design of the water jet cutting head promotes integration with motion
control systems ranging from two-axis (XY) tables to sophisticated multiaxis robotic
installations.
Recommended Nozzle Material Operating Conditions
Carbide Dirty, unfiltered water, Pressure below
140 MPa

Steel Water filtered to 25 micron or better, pressure

below 140 MPa

Sapphire Water filtered to micron or better,

Pressures above 140 MPa

Diamond nozzle shows better performance over sapphire nozzle at high pressure in
terms of jet stability.

6. Catcher
 Acts as a reservoir for collecting the machining debris entrained in the water jet.
 Moreover, it reduces the noise levels [105 decibels (dB)] associated with the reduction
in the velocity of the water jet from Mach 3 to subsonic levels.

1.12.1 Process Parameters Affecting WJM

JET Nozzle
 Standoff distance - Gap between the jet nozzle (0.1 - 0.3 mm diameter) and the
workpiece (2.5 - 6 mm).
 However for materials used in printed circuit boards, it may be increased to
13 to 19 mm.
 But larger the standoff distance, smaller would be the depth of cut.
  When cutting fiber-reinforced plastics, reports showed that the increase in machining
rate and use of the small nozzle diameter increased the width of the damaged layer.

JET Fluid
 Typical pressures used are 150 to 1000 MPa to provide 8 to 80 kW of power.
 For a given nozzle diameter, increase in pressure allows more power to be used in the
machining process, which in turn increases the depth of the cut.
 Jet velocities range between 540 to 1400 m/s.
 The quality of cutting improves at higher pressures by widening the diameter of the jet
and by lowering the traverse speed.
 Under such conditions, materials of greater thicknesses and densities can be cut.
 Moreover, the larger the pump pressure, the greater will be the depth of the cut.
 The fluid used must possess low viscosity to minimize the energy losses and be
noncorrosive, nontoxic, common, and inexpensive.
 Water is commonly used for cutting alloy steels.

Workpiece
 Brittle materials will fracture, while ductile ones will cut well.
 Material thicknesses range from 0.8 to 25 mm or more.
 Table above shows the cutting rates for different material thicknesses.

Material Thickness, mm Feed rate, m/mim

Leather 2.2 20

Vinyl chloride 3.0 0.5

Polyester 2.0 150

Kevlar 3.0 3

Graphite 2.3 5

Gypsum board 10 6

Corrugated board 7 200

Pulp sheet 2 120

Plywood 6 1
Applications
 WJM is used on metals, paper, cloth, leather, rubber, plastics, food, and ceramics.
 It is a versatile and cost-effective cutting process that can be used as an alternative to
traditional machining methods.
 It completely eliminates heat-affected zones, toxic fumes, recast layers, work hardening
and thermal stresses.
 It is the most flexible and effective cleaning solution available for a variety of industrial
needs.
 In general the cut surface has a sandblast appearance.
 Moreover, harder materials exhibit a better edge finish.
 Typical surface finishes ranges from 1.6 μm Root Mean Square (RMS) to very coarse
depending on the application.
 Tolerances are in the range of ± 25 μm on thin material.
 Both the produced surface roughness and tolerance depend on the machining speed.

1. Cutting
 WJM is limited to fibreglass and corrugated wood.
 Fig. 1.19 shows typical example of water jet cutting of water jet cutting of marble and
application in the food industry.

Fig. 1.19 Applications of WJM in marble cutting and food industries

2. Drilling
 The process drills precision-angled and -shaped holes in a variety of materials for which
other processes such as EDM or EBM are too expensive or too slow.

3. Machining of fiber-reinforced plastics

 In this case the thermal material damage is negligible.
 The tool, being effectively pointed, accurately cuts any contours.
 The main drawback is the deflection of the water jet by the fiber embedded in the
matrix, which protrudes after machining.
  The feed rate attainable depends on the surface quality required.
 Table below gives the limiting feed rates for water jet cutting of fiber-reinforced
plastics.
Material Thickness, mm Feed rate, m/min

Glass fiber-reinforced polymers 2.2 1.8 – 6.0

(GFRP) (laminate) 3.0 1.4 – 5.0
5.0 0.7 – 6.0

Aramid fiber-reinforced 1.0 10.0

polymers (AFRP) (weave) 2.0 2.4 – 4.0

4. Cutting of rocks
 Water jet cutting of a 51 mm deep slot in granite using two oscillating jets at 275 MPa
during 14 passes at a 25.4 mm/s feed rate has been reported by McGeough (1988).
 Moreover an oscillating nozzle system operating at the same feed rate and pressure of
172 MPa, with the standoff distance adjusted every pass was used to cut a 178 mm deep
slot in sandstone.

5. Deburring
 The method uses large pressures to remove large burrs (3 mm height) in 12 mm
diameter drilled holes in a hollow molybdenum-chromium steel shaft at 15 s using
700 bar pressure and a flow rate of 27 L/min.
 In this method burrs are broken off by the impact of water.
 A higher pressure (4000 bar) and a lower flow rate (2.5 L/min) are used to remove burrs
from nonmetallic materials.

6. Cutting of PCBs
 Using a small-diameter water jet, a printed circuit board (PCB) can be cut at a speed that
exceeds 8 m/min, to the accuracy of ± 0.13 mm.
 Boards of various shapes for use in portable radios and cassette players can be cut using
Computer Numerical Control (CNC) technology.

7. Surface treatment
 Removing deposits and residues without toxic chemicals, which eliminates costly clean
up and disposal problems.
  Surface cleaning of pipes and castings, decorative finishing, nuclear decontamination,
food utensil cleaning, degreasing, polishing, preparation for precise inspection, and
surface texturing.
 Economical surface preparation and coating removal.
 Removing corrosion, spray residue, soluble salts, chemicals, and surface damage prior
to recoating or painting.

8. Wire stripping
 Can remove the wire insulating material without damaging the metal or removing the
tinning on the copper wire.
 Processing time can be decreased to about 20 % of the manual stripping method.

Advantages
 It has multidirectional cutting capacity.
 No heat is produced.
 Cuts can be started at any location without the need for predrilled holes.
 Wetting of the workpiece material is minimal.
 There is no deflection to the rest of the workpiece.
 The burr produced is minimal.
 The tool does not wear and, therefore, does not need sharpening.
 The process is environmentally safe.
 Hazardous airborne dust contamination and waste disposal problems that are common
when using other cleaning methods are eliminated.
 There is multiple head processing.
 Simple fixturing eliminates costly and complicated tooling, which reduces turnaround
time and lowers the cost.
 Grinding and polishing are eliminated, reducing secondary operation costs.
 The narrow kerf allows tight nesting when multiple parts are cut from a single blank.
 It is ideal for roughing out material for near net shape.
 It is ideal for laser reflective materials such as copper and aluminum.
 It allows for more accurate cutting of soft material.
 It cuts through very thick material such as 383 mm in titanium and 307 mm in Inconel.
Limitations
 Very thick parts can not be cut with water jet cutting and still hold dimensional
accuracy. If the part is too thick, the jet may dissipate some, and cause it to cut on a
diagonal, or to have a wider cut at the bottom of the part than the top. It can also cause a
rough wave pattern on the cut surface.
 It is not suitable for mass production because of high maintenance requirements.

Water Jet Lag

Recent developments in WJM
 High pressure water jet
 Nozzle shape

Fig. 1.20

 Water jet forming  Water jet peening

 Water jet in mining  Water jet in packaging industry
 Water jet in food processing plant  Water jet guided laser technology
 Medical applications

1.13 Ultra-Sonic Machining

 The term ultrasonic is used to describe a vibratory wave of a frequency above that of the
upper limit of the human ear.
 There are two types of waves namely shear wave and longitudinal wave.
 Longitudinal waves are mostly used in the ultrasonic applications, since they are easily
generated.
Construction
 Fig. 1.21 shows the whole setup of Ultra Sonic Machining method. It consists of an
electromechanical transducer for producing frequency upto 20 kHz to 30 kHz, which is
more than the upper limit of audible frequency of the human ear, and makes the process
silent.
 It also uses slurry of small abrasive particles which is forced against the workpiece by using
a vibrating tool and it removes the material of workpiece in the form of small chips.
 The tool which is applied to the workpiece is generally made of soft materials and slurry is
fed either manually or through pump. Sometimes hollow tools are also used because the
slurry can feed through it easily.
 The transducer used in the process is made up of a magneto structive material, which is
excited by the high frequency electric current and generates mechanical vibrations

Working

Fig. 1.21 Principal components of an ultrasonic machine

 A high frequency electric current is supplied by the ultrasonic oscillator to the ultrasonic
transducer, which converts electrical energy into mechanical vibrations.
 To get the amplitude from 0.01 mm to 0.1 mm, vibrations of 20 kHz to 30 kHz are
generated.
 These vibrations are transmitted to the cutting tool through the transducer cone, connecting
body and tool holder.
 Due to these vibrations, tool vibrates in a longitudinal direction as shown in Fig. 1.21.
 The shape of the cutting tool is mirror image as that of which is produced on the workpiece.
 USM is also called as Ultrasonic Grinding or Impact Grinding.
Equipment :
Ultrasonic machining consists of :
1. Ultrasonic transducer 2. Concentrator
3. Tool 4. Abrasive slurry
5. Abrasive feed mechanism 6. Tool feed mechanism

Fig. 1.22 Schematic representation of ultrasonic machining process

1. Ultrasonic transducer
The equipment consists an ultrasonic transducer for which the electrical input is given, to
obtain the required mechanical vibration. The device used for converting any type of energy
into ultrasonic waves or vibrations is called ultrasonic transducer. The electrical energy is
converted into mechanical vibrations for carrying out the machining operation. The high
frequency electrical signal is transmitted to traducer which converts it into high frequency low
amplitude vibration. Essentially transducer converts electrical energy to mechanical vibration.
There are two types of transducer used

i) Piezo electric transducer ii) Magneto-stricitve transducer.

i) Piezo electric transducer
 Piezo electric transducer have the capability of converting electrical energy into
mechanical vibrations.
 These transducer generate a small electric current when they are compressed. Also when
the electric current is passed though crystal it expands.
 When the current is removed, crystal attains its original size and shape. Such transducers
are available up to 900 Watts. Piezo electric crystals have high conversion efficiency of
95 %.
o More efficient
o Less loss of power
o Do not require cooling
ii) Magneto-strictive transducer :
 These also changes its length when subjected to strong magnetic field. (Magnetostrictive
effect is the one in which the material changes its dimensions in response to a magnetic
field).
 These transducer are made of nickel, nickel alloy sheets. Their conversion efficiency is
about 20-30 %. Such transducers are available up to 2000 Watts.
 The maximum change in length can be achieved is about 25 microns.

Fig. 1.23

 The magnetostrictive transducer consists of an excitation coil wound around a laminated

nickel core.
  The magnetostrictive materials employed are nickel, Iron-cobalt called Permendur, Iron-
Aluminium as Alfer.
 Nickel is widely used because of its high strength and good insulating property. The
nickel core present in the transducer unit contracts and expands in response to the
influence of a rapidly alternating current.
 Under the action of the electromagnetic field, set up by the input electrical power
supply, the magnetostrictive stack is periodically magnetized and its length changes.
The periodical shortening and lengthening of the stack in synchronous with the
generator frequency and initiates the vibration.
 The amplitude of vibration is of the order between 0.1 mm to 0.06 mm. Eddy current
losses of the transformer can be reduced by using Ferro-magnetic material in the form of
insulated laminations assembled into a pack.
 A fair amount of the given input energy to the transducer appears as a heat so cooling is
necessary. If the machine is up to 50 W capacity, air cooling is sufficient. But for higher
capacity 50 W water cooling must.
 Magnetostrictive transducer,
o Generally found in old machines
o Less efficient due to high eddy current losses
o Requires cooling.
 The transducer may be of Piezo-electric or Magnetostrictive type depending upon the
choice of the choice of operation to be performed on a specific work piece materials.
 The amplitude of vibration obtained from the transducer is inadequate for doing any
operation and hence the tool is connected to the transducer by means of a concentrator
to produce the desired amplitude at the tool end.

Notes : The electrical input circuit of an ultrasonic transducer consists of an ultrasonic

oscillator and power amplifier (Also called generator) which converts low frequency
Electrical energy (50 Hz) to High Frequency electrical energy (25 kHz).

2. Concentrator or tool holder or horn

 Concentrator provides the link between the tool and transducer. It is also called as tool
cone, horn, and wave guide or tool holder. The tool holder holds and connects the tool
to the transducer. It virtually transmits the energy and in some cases, increases the
amplitude of vibration.
  The different types of concentrators used are,
1. Exponential type
2. Conical type
3. Stepped type

Fig. 1.24

Concentrator materials
 The horn or concentrator are generally made of monelmetal or stainless steel or titanium
alloy or aluminium which can be fitted to the transducer either by brazing or to a
connecting body made of Monel metal at a fixed nodal point.
 Monel metal (Monel is a group of nickel alloys, primarily composed of nickel (up to
67 %) and copper, with small amounts of iron, manganese, carbon, and silicon.) is the
best one to be used as a tool holder which has properties of same as titanium and it can
also be brazed easily.
 Stainless steel is not preferred because of its low fatigue strength. It is used only for
low amplitude applications.
The tool holders or concentrators are available as

i) Non-amplifying type ii) Amplifying type

i) Non-amplifying types produce the same amplitude of vibration at end where the tool
is connected to the given input amplitude. They are normally of cylindrical cross
section.
 ii) Amplifying tool holders are capable of amplifying at end where the tool is connected
and remove materials 10times faster than the non-amplifying type.

Disadvantages of amplifying concentrator :

o Higher fabrication cost.
o Poor surface finish.
o Need for frequent tuning to maintain resonance.
o Tool holders are more expensive, demand higher operating cost.

3. Tool
 Tool is normally fixed at the end of the concentrator.
 It is fixed either by brazing, soldering or fastened to the concentrator.
 It must be ductile and tough rather than hard.
 As the ratio of the work piece hardness and tool hardness increases the MRR decreases.
 In practice slenderness ratio of the tool should not exceed 20.
 A smaller contact area enhances better abrasive flow and so high penetration is obtained.
 Also if the cutting path is long, due to poor scavenging from the innermost areas, the
cutting is inefficient.
 The tool shape is normally the mirror image of the cavity to be produced along with the
tolerance for abrasive particle size and tool wear considerations.
 Sonotrode : In ultrasonic machining, welding and mixing, a sonotrode is a tool that
creates ultrasonic vibrations and applies this vibrational energy to a gas, liquid, solid or
tissue. Sonotrodes of small diameter are sometimes called probes.

Note : The tool tip or tool face can be made from diamond, tool steel, Stainless steel, cold
rolled steel, brass or copper.

4. Abrasive slurry
 The abrasive slurry is nothing but a mixture of abrasive grains and the carrier fluid
generally water. The abrasive slurry is circulated by a pump between the tool and work
piece interface.
 Some of the abrasive used are,
1. Aluminium Oxide (Al2O3 Alumina) 2. Boron carbide (B4C)
3. Silicon carbide (SiC) 4. Diamond dust
5. Boron silicarbide
 Boron carbide
 Best and most efficient and fastest cutting abrasive.
 Expensive
 Used for cutting harder materials like tungsten carbide, tool steel
and precious stones.

Silicon carbide
 Used for glass, germanium and some ceramics
 Used for maximum application
Alumina
 Less efficient than boron carbide
Aluminium oxide
 Loses its cutting ability due to poor wear resistance.

 Abrasives for USM are generally available in grit sizes ranging from 240 - 1000.
Grade Grit size Application
Coarse grits 200 - 400 Roughing work

Finer grits 800 - 1000 Finishing work

Fine Finishing work

Extremely fine grits 1200 - 2000
(Where extreme accuracy is demanded)

 Selection of abrasives depends on hardness, usable life, cost and particle size.
 Fresh abrasives are preferred because of their good cutting ability and to sustain the
removal rate.

Carrier Fluids
 The abrasive material is mixed with water (Carrier Fluid) to form an abrasive slurry.
 The most common abrasive concentration is water with 30 – 40 % by volume of the
abrasives.
 The thinner mixtures are used to promote efficient flow when drilling holes or when
forming complex cavities.
 The abrasive slurry should be replaced periodically.
 When water is used as a carrier fluid, some inhibitors are added to the water to improve
its performance.

Notes : Other carrier fluids used are Benzene, Glycerol and some low viscosity oils.
 Characteristics of carrier fluids
 Density approximately equal to that of the abrasives.
 Good wetting characteristics.
 High thermal conductivity and specific heat for efficient heat removal from the cutting
area.
 Should have low viscosity.
 Should be non-toxic and easily available at cheap rate.
 Should be non-corrosive.
Functions of carrier fluid in USM
 Acts as an acoustic bond between the work piece and the tool.
 Acts as a coolant.
 Helps efficient transfer of energy.
 Acts as medium to carry the abrasive, machined materials and worn abrasives.

5. Abrasive feed mechanism

 Abrasive slurry is supplied through a nozzle by a pump. A good method is to keep the
tool and the work piece in a bath of slurry.
 This ensures good supply of slurry and reduces any tendency of the tool to scatter the
slurry when the amplitude is large.
 Another efficient method is to supply the slurry to the cutting zone through a hollow
tool or through holes in the work piece.

6. Tool feed mechanism

 The objective of the tool feed mechanism is to apply the static load between the tool and
the workpiece, during machining operation.
 It also brings the tool slowly, close to the workpiece surface and provides adequate,
constant cutting force, then aids for the return of the tool as when desired. The
sensitivity of feed is very important.
 Feed may either be given to the acoustic head or to the work piece, but in general feed
motion is given to the acoustic head so as to facilitate positioning of the workpiece in
X-Y direction.
 The tool feed mechanism controls the penetration rate and the depth of machining.
 Functions of tool feed mechanism :
1. Bring the tool close to the workpiece, giving place for abrasive flow.
2. To provide the required impact force or cutting force and maintain throughout the
operation as required.
3. Return the tool smoothly without damaging the cavity produced.

Types of feed mechanism

1. Spring type 2. Counter-weight type

3. Motor type 4. Pneumatic and hydraulic type

1. Spring type feed mechanism

 In this mechanism spring pressure is used to feed the tool during machining operation.
This type of mechanism is preferred for its sensitivity and compactness.

2. Counter-weight type feed mechanism

 This mechanism is also called Gravity feed mechanism.
 In this mechanism, counter weight are used to apply the load to the head through a
pulley as shown in Fig. 1.25(a) In order to reduce the friction, ball bearing are used.
 This mechanism is preferred for its simple construction. The force can be adjusted by
varying the counter weights.
 This type is insensitive and inconvenient for adjustability during the operation.

3. Pneumatic and hydraulic type feed mechanism

 This is used for high rating machines. In order to get high feed rate, pneumatic feed
mechanism is used.
 All the above types are provided with a tool displacement reading arrangement to know
about the depth of penetration.

Working Principle
 When an AC power supply is given to the transducer, due to excitation, the transducer
vibrates and the vibration is amplified by the horn or concentrator.
 The amplitude of vibration is maximum at the end of the tool holder where the tool is
attached. The tool vibrates at the maximum frequency.
 Fig. 1.25 Different types of feeding arrangements for USM

 The tool is fed on to the workpiece surface along with the supply of abrasive slurry. As
the tool during vibration goes up and comes down, the abrasive particles entrapped
between the tool and the workpiece surface are given impact on the workpiece surface.
  This impact causes the fracture and the particles are carried away by the circulating
slurry of abrasive. Since the tool is the mirror image of the cavity to be produced, the
tool feed mechanism aids for the formation of the cavity to the required shape.

Work Material
 Material removal method involved in this process is brittle fracture and obviously works
only on relatively brittle materials.
 Any hard materials like stones, carbides, ceramics and brittle materials can also be
machined.
 Any materials having high hardness >50 HRC like stainless steel, germanium, glass,
ceramics etc., can be machined.

Mechanism and Material Removal

 In ultrasonic machining an abrasive slurry is pumped between tool and work, and the
tool is given a high frequency, low amplitude oscillation, which in turn, transmits a high
velocity to fine abrasive particles which are driven against the workpiece.
 At each stroke, minute chips of material are removed by fracture or erosion. Material
Removal Mechanism involves both fracture and plastic deformation by impact of grains
due to vibrating tool.

1.13.1 Process Variables of USM

1. Effect of amplitude and frequency of vibration on MRR

 Different researchers have different predictions on the effect of amplitude on MRR.

 Rozenberg found that for a given material, the MRR is proportional to the square of
the amplitude.
 Miller has shown that the cutting rate bears a liner relationship with amplitude.
According to him the MRR increase in amplitude and frequency.
 Shaw showed that MRR is proportional to amplitude 3/4. He also predicted that the
MRR is directly proportional to the first power of frequency for a fixed amplitude.

 Increases in frequency increases the number of blows on the grain particles impinging
on the workpiece surface. So the MRR increases almost linearly with frequency.
 Fig. 1.26

2. Effect of particle velocity

 Markov has shown that the MRR is directly proportional to the particle velocity. So
particle velocity increases the number of particles per impinging per unit time also
increases.

3. Effect of static loading or feed force

 The MRR increases with an increase in the feed force. But it tends to decrease beyond a
critical value of the force, since the magnitude of the force crushes the abrasive grains
thus decreasing its cutting ability and the MRR.
 As the feed force is more, the surface finish is good, because the grains are crushed to
smaller size.

4. Effect of grain size

 As the grain size increases MRR also increases proportionally. However Grain size
increases the MRR also increases till the grain size equals the amplitude of vibration.
Beyond this, the MRR decreases due to effect of crushing of grains.

5. Effect of hardness ratio

 The ratio of workpiece hardness to tool hardness affects the MRR significantly in a way
that as the ratio increases the MRR decreases according to the trend shown in graph.
 The Brittle materials are machined more rapidly than the ductile materials.

6. Effect of grain size (Grain diameter)

 Regarding the surface finish, when the grain size increases the surface roughness also
increases and vice versa.
 Grain size also affects the accuracy of the cavity to be produced. Normally the hole is
cut larger than the size of the tool owing to the flow of abrasive slurry along the sides
and bottom of the tool.
7. Effect of viscosity
 The MRR drops appreciably when the viscosity increases, because the increase in
viscosity tends to dampen the oscillations of the grains, thus decreasing the energy
provided on the workpiece.

8. Effect of abrasive slurry concentration

 The abrasive slurry should flow easily under the gap between the tool and the workpiece
surface.
 The slurry concentration directly controls the number of grains producing impact and
the magnitude of the impact.
 The concentration increases the MRR also increases. The trend of increase in the
number of grain for the unit volume of liquid media disturbing the power of impact to
all the grains.

1.13.2 Process Capability

1. Can machine work piece harder than 40 HRC to 60 HRC like carbides, ceramics,
tungsten glass that cannot be machined by conventional methods
2. Tolerance range 7 micron to 25 microns
3. Holes up to 76 micron have been drilled hole depth upto 51mm have been achieved
easily. Hole depth of 152 mm deep is achieved by special flushing techniques.
4. Aspect ratio 40:1 has been achieved
5. Linear material removal rate – 0.025 to 25 mm/min
6. Surface finish – 0.25 micron to 0.75 micron
7. Non directional surface texture is possible compared to conventional grinding
8. Radial over cut may be as low as 1.5 to 4 times the mean abrasive grain size.

Material removal models in USM

Theoretical analysis and experimental results have revealed that USM is a form of abrasion
and material removal in the form of small grains by four mechanisms
1. Throwing of abrasive grains
2. Hammering of abrasive grains
3. Cavitation’s in the fluid medium arising out of ultrasonic vibration of tool.
4. Chemical erosion due to micro – agitation
 Material removal due to throwing and hammering is significant and MR due to cavitation
and chemical erosion can be ignored. Abrasive particles are assumed to be spherical in shape
having diameter (dg). Abrasive particles move under high frequency vibrating tool.
There are two possibilities when the tool hit the particle.
 If the size of the particle is small and gap between the tool and work is large, then
particle will be thrown by tool to hit the work piece.
 If the size of the particle is large and gap between tool and work is small, then particle is
hammered over the work surface.

Advantages
1. It can be used machine hard, brittle, fragile and non-conductive material.
2. No heat is generated in work, therefore no significant changes in physical structure of
work material.
3. Non-metal (because of the poor electrical conductivity) that cannot be machined by
EDM and ECM can very well be machined by USM.
4. It is burr less and distortion less processes.
5. Capability of drilling circular, no-circular holes in very hard materials like stones,
carbides, ceramics and exceptionally brittle materials.
6. Bur less process.
7. No thermal effects on the machined workpiece.
8. Low cost of metal removal.
9. It can be adopted in conjunction with other new technologies like EDM, ECG, and
ECM.
10. Equipment is safe to operate.

Disadvantages
1. Low metal removal rate. Not suitable for heavy stock removal.
2. It is difficult to drill deep holes, as slurry movement is restricted.
3. Tool wear rate is high due to abrasive particles. Tools made from brass, tungsten
carbide, MS or tool steel will wear from the action of abrasive grit with a ratio that
ranges from 1:1 to 200:1
4. USM can be used only when the hardness of work is more than 45 HRC.
5. Frequent tuning is required.
6. Not economical for soft materials.
Limitations
1. Low MRR
2. Depth of cylindrical holes produced is limited by the abrasive transport system.
3. High tooling cost.
4. Periodic replacement of abrasive slurry.
5. Tendency of tools to ‘break out’ at the bottom owing to static load and amplitude.
6. Inability to machine soft material.

Applications
1. Machining of cavities in electrically non-conductive ceramics
2. Diamond, tungsten, tungsten carbide, gem stones and synthetic ruby can be
successfully machined.
3. Used to machine fragile components.
4. Used for multistep processing for fabricating silicon nitride (Si3N4) turbine blades
5. Large number of holes of small diameter. 930 holes with 0.32 mm has been reported
(Benedict, 1973) using hypodermic needles
6. Used for machining hard, brittle metallic alloys, semiconductors, glass, ceramics,
carbides etc.
7. Used for machining round, square, irregular shaped holes and surface impressions.
8. Used in machining of dies for wire drawing, punching and blanking operation
9. USM can perform machining operations like drilling, grinding and milling operations
on all materials which can be treated suitably with abrasives.
10. USM has been used for piercing of dies and for parting off and blanking operations.
11. USM enables a dentist to drill a hole of any shape on teeth without any pain
12. Ferrites and steel parts, precision mineral stones can be machined using USM
13. USM can be used to cut industrial diamonds
14. USM is used for grinding Quartz, Glass, ceramics, Cutting holes with curved or spiral
centre lines and cutting threads in glass and mineral or metallic-ceramics
15. Gang drilling can be done by employing USM process.
 Fig. 1.27 Some applications of USM

1.14 Two Marks Questions with Answers

Part - A
What are the characteristics of unconventional machining process ? (Section 1.1.1)
List the unconventional machining process, which uses mechanical energy.
Ans. :
 Abrasive Jet Machining
 Abrasive Water Jet Machining
 Water Jet Machining
 Ultrasonic Machining.
What is the necessity for UCMP ? (Section 1.1.2)
How non-traditional machining processes are classified. (Section 1.3)
What are the importances of UCMP ? (Section 1.1.2)
Explain the classification of UCMP according to major energy source employed.
(Section 1.3)
Q.7 Distinguish traditional and non-traditional machining process. (Section 1.2)
Q.8 What types of energy are employed in non-traditional machining process ?
(Section 1.4)
Q.9 Enlist the requirement that demands the use of advanced machining process.
(Section 1.1.2)
Q.10 Why unconventional machining process is not so effective on soft materials like
Aluminium?
Unconventional machining process is not so effective on soft metals like aluminium,
Ans. :

because accuracy cannot be maintained due to more metal removal rate.

Q.11 How will you compare various non-traditional processes ? (Section 1.3.1)
Q.12 What are the different machining characteristics with respect to which the non
traditional machining process can be analysed ?
Ans. : Material removal rate, accuracy, surface finish, cutting speed, feed, depth of cut
Q.13 What are the industrial needs for unconventional machining processes ?
Ans. : To machine high steel alloys.
To generate desired complex surfaces and.
To achieve high accuracy and surface finish.
Q.14 Write down the energy transfer media, energy source and mechanism of metal
removal for the following process.
Ans. : a) Water Jet Machining b) Electrochemical Grinding.

Processes Energy transfer Energy source Mechanism of

media metal removal

Water Jet Machining High velocity water Hydraulic pressure Erosion

jet

Electrochemical Electrolyte Electrical source and Ion displacement

Grinding. mechanical
movement
Q.15 Name the important factors that should be considered during the selection of an
unconventional machining process for a given job.
Ans. :
i) Physical parameters
ii) Shapes to be machined
iii) Process capability or machining characteristics
iv) Economic considerations.
Q.16 Classify modern machining process on the basis of the type of energy employed.
mechanical, thermal, chemical and electrochemical.
Q.17 Mention thermal energy based unconventional machining process.
laser beam machining, plasma arc machining, electron beam machining.
Q.18 What are the advantages of unconventional machining processes ?
Ans. :  High accuracy and surface finish.
 No direct contact of tool and workpiece, so there is less/no wear.
 Quieter operation.
Q.19 List the unconventional machining process based on chemical energy
Ans. : Chemical Machining, Electro Chemical machining, Electro Chemical Grinding
Q.20 Suggest a suitable unconventional machining process to cut a thin glass plate into two
pieces.
Ans. : Process like ECM, EDM, PAM, EBM are ruled out because they are suitable to
machine only electrically materials
WJM, AWJM, USM can be used for machining.
Based on accuracy required any one process can be selected.
Q.21 What is the transfer medium in AJM ?
Ans. : High velocity particles.
Q.22 Write the applications of AJM. (Section 1.10.2)
Q.23 List any four variables in AJM that influence the MRR.
Ans. : Carrier Gas, Jet Velocity, Stand of distance, mixing ratio.
Q.24 What are the various abrasives used in AJM process ?
Ans. : Uniform particles of sand, steel grit, copper slag, walnut shells, and
powdered abrasives are used.
Q.25 Why abrasive jet machining process is not recommended to machine ductile
materials.
Ans. : While machining ductile materials by AJM, the hard abrasive grits may get embedded
on the soft machined surface. This obstructs cut quality as well as properties and appearance
of machined surface.
Q.26 Write the formula for MRR for ductile and brittle materials in AJM.
Ans. :
Mg  U3/2
 MRRbrittle = 1.04 1/4 3/4
g H
MgU2
 MRRductile = 0.5 H
U = Velocity of abrasive jet at the point of impact.
 H = Flow strength or hardness of the work material.
Mg = Mass flow rate of abrasive particles.
ρg = Density of each abrasive particle.
Q.27 Reuse of abrasives is not recommended in AJM process. Why ?
Ans. : Reuse of abrasives is not recommended since the cutting ability of abrasive decrease
after the usage and also the contamination of wear materials clogging the nozzle and the
cutting unit orifice.
Q.28 What is the principle of WJM ? (Section 1.12 (Principle))
Q.29 List the applications of WJM. (Section 1.12.1 (Applications))
Q.30 List the process parameters of WJM.
Ans. : Jet Nozzle, jet Fluid, Workpiece
Q.31 Mention the application of catcher in water jet machining.
Ans. : Acts as a reservoir for collecting the machining debris entrained in the water jet.
Moreover, it reduces the noise levels associated with the reduction in the velocity of the
water jet.
Q.32 List out the limitations of WJM process.
Ans. : Very thick parts cannot be machined.
It is not suitable for mass production because of high maintenance requirements.
Q.33 Write the typical applications of ultrasonic machining.
Ans. :  Machining very precise and intricate shaped articles.
 Drilling the round holes of any shape.
 Grinding the brittle materials.
 Profiling the holes.
 Engraving.
 Trepaning and coining.
Q.34 What is the effect of abrasive grain size on machining rate in USM ?
(Section 1.13.1 (Point no. 6))
Q.35 What is the need for transducer in USM ?
Ans. : The transducer, which generates the ultrasonic vibration based on piezoelectric effect.
It converts electrical energy to mechanical vibrations.
Q.36 State the working principle of USM. (Section 1.13 (Working))
Q.37 List the applications of USM ? (Section 1.13.1(Applications))
Q.38 List the process parameters of USM.
Ans. : Effect of particle velocity
Effect of grain size
 Effect of hardness ratio
Effect of viscosity.
Q.39 List out the abrasive materials used in ultrasonic machining process.
Ans. : Silicon Carbide, Aluminium Oxide, Boron Carbide
Q.40 What are the advantages of ultrasonic machining? (Section 1.13.2 (Advantages))

1.15 Long Answered Questions

Part - B
Q.1 Compare the mechanical and electrical energy processes in terms of physical
parameters, shape capabilities, process capability and process economy.
(Section 1.3.1)
Q.2 Explain the reasons for the development of UCMP. Discuss about the criteria
recommended in selection of these processes. (Sections 1.1.2 and 1.4.4)
Q.3 i) Explain the factors that should be considered during the selection of an appropriate
unconventional machining process for a given job. (Section 1.8)
ii) Compare and contrast the various unconventional machining process on the basis
of the type of energy employed, material removal rate, transfer media and
economical aspects. (Section 1.4.4)
Q.4 Make a comparison between traditional and unconventional machining processes in
terms of cost, application, scope, machining time, advantages and limitations.
(Section 1.2)
Q.5 For different non-conventional processes, present in the form of table, various
process parameters recommended. (Section 1.8)
Q.6 How will you analyse the applicability of different processes to different types of
materials, namely metals, alloys and non-metals ? Presentation in the form of table
is preferred. (Section 1.5.3)
Q.7 What are the basic limitations of conventional manufacturing process ? Justify the
need of unconventional machining process in today’s industries.
(Sections 1.1 & 1.1.1)
Q.8 Explain the principle of working of the AJM process with its advantages,
disadvantages, limitations and applications. (Sections 1.10 and 1.10)
Q.9 With a neat sketch explain the operation and effect of process parameters of AJM. List
the applications. (Sec 1.10.2 (Process Parameter))
Q.10 Explain the principle of AJM. Mention some of the specific applications. Discuss in
detail about the AJM process variables that influence the rate of material removal
and accuracy in the machining. (Sections 1.10 and 1.10.2)
Q.11 Write the names of various elements of Abrasive Jet Machining (AJM) and explain
them in brief. (Sec 1.10 (Equipment))
Q.12 Compare the types of nozzle design employed in AWJM with neat sketches. (Fig 1.11)
Q.13 Describe the process parameters of abrasive Jet machining along with the effect of all
the process parameters. (Section 1.10.2)
Q.14 Explain the different applications and process control features of WJM. Describe the
principle and equipment for WJM. (Section 1.12)
Q.15 Discuss the process parameters in WJM process. (Section 1.12.1)
Q.16 List the application and limitation of WJM. (Section 1.12.1 (Application and
Limitations))
Q.17 Explain the principle of Ultrasonic Machining (USM) and its equipment. Explain the
factors which influence the Metal Removal Rate (MRR) in USM.
(Sections 1.13 and 1.13.1)
Q.18 Explain the following in detail.
a. Types of Transducers for USM (Section 1.13 (Transducer ))
b. Feed Mechanisms in USM. (Section 1.13 (Types of feed mechanism ))
c. Typical Applications of USM. (Section 1.13.2 (Applications))
d. Abrasives for USM. (Section 1.13 (Abrasive Slurry ))
Q.19 List the various types of tool holders and transducers used in ultrasonic machining
and explain them briefly.
(Section 1.13 (Transducer), Section 1.13 (Types of feed mechanism))
Q.20 Discuss the effects of the following parameters on the MRR and surface finish in
USM. (Section 1.13.1)
a. Amplitude and frequency
b. Abrasive rates
c. Concentration of abrasives
d. Material hardness.
Q.21 Explain the USM machine Set-up and discuss various feed mechanisms.
(Section 1.13 (Types of feed mechanism))
Q.22 Explain the principle of USM with neat diagram. (Section 1.13)
Q.23 List the commonly used abrasive powder for the tooling of USM and their properties.
(Section 1.13 (Abrasive Slurry))
Q.24 Discuss in detail about the methods of generating the ultrasonic, characteristics of the
various types of tool holder and tool feed mechanisms in USM. (Section 1.13)
Q.25 Compare USM. WJM and AJM in terms of process capabilities and limitations.
(Section 1.5.2)
Q.26 How are ultrasonic vibrations generated in USM process? (Section 1.13)
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1.16 Multiple Choice Questions with Answers

INTRODUCTION

Q.1 Non-traditional machining is recommended when we need which of the following

features ?
a Complex shapes b High surface quality
c Low-rigidity structures d All of the mentioned [Ans. : d]

Q.2 Non-traditional machining can also be called as .

a contact machining b non-contact machining
c partial contact machining d half contact machining [Ans. : b]

Q.3 In which of the following industries, Non-traditional machining methods play an

important role ?
a Automobile b Aerospace
c Medical d All of the mentioned [Ans. : d]

Q.4 Different classifications of Non-traditional machining based on source of energy are

.
a mechanical b thermal
c chemical and electro-chemical. d all of the mentioned [Ans. : d]

Q.5 In mechanical machining, material is removed by

a erosion b corrosion
c abrasion d vaporization [Ans. : a]

Q.6 Material in thermal machining is removed by which of the following means ?

a Vaporization b Melting
c Electro-plating d All of the mentioned [Ans. : d]

Q.7 Which of the following process comes under mechanical machining ?

a USM b EDM
c LBM d PAM [Ans. : a]

Q.8 Surface defects that may be occurred during thermal machining are .
a micro cracking b heat affected zones
c Striations d all of the mentioned [Ans. : d]

Q.9 Sources used in thermal machining are .

a ions b plasma
c electrons d all of the mentioned [Ans. : d]

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Q.10 Vacuum is the machining medium for .

a LBM b WJM
c EBM d none of the mentioned [Ans. : a]

Q.11 In chemical machining is material removal takes by ?

a Chemical reaction b Erosion
c Electron removal d None of the mentioned [Ans. : a]

Q.12 Which of the following is an example of hybrid machining ?

a Ultrasonic Machining b Electron Beam Machining
c Ultrasonic assisted electrochemical machining
d Laser Beam Machining [Ans. : c]

ABRASIVE JET MACHINING

Q.13 In advanced machining processes, what is the full form of AJM ?

a Automatic Jet Manufacturing b Abrasive Jet Machining
c Automated Jet Machining d Abrasive Jet Manufacturing [Ans. : b]

Q.14 In AJM, which of the following materials are used as abrasive grains ?
a Al2O3 b SiC

c Glass beads d All of the mentioned [Ans. : d]

Q.15 In abrasive jet machining, work piece material is removed by which of the following
means ?
a Vaporization b Electro plating
c Mechanical abrasion d Corrosion [Ans. : c]

Q.16 Which type of materials can be machined using abrasive jet machining ?
a Glass b Ceramics
c Hard materials d All of the mentioned [Ans. : d]

Q.17 In machining system of AJM, which is the medium of carrying the abrasive grains for
machining ?
a Liquids b Gases
c Any fluids d None of the mentioned [Ans. : b]

Q.18 In machining system of AJM, what is/are the gas/es used for carrying the abrasives?
a CO2 b Air
c Nitrogen d All of the mentioned [Ans. : d]

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Q.19 What is the pressure of gas that is to be supplied, for carrying the abrasives ?
a 0.1 to 1.0 kg/cm2 b 2.0 to 8.0 kg /cm2
c 10.0 to 18.0 kg/cm2 d 25.0 to 35.5 kg/cm2 [Ans. : b]

Q.20 Which of the following gas, should never be used as the carrier of abrasives ?
a Nitrogen b CO2
c Oxygen d Air [Ans. : c]

Q.21 What is the frequency of mixing chamber, consisting of gas and abrasives ?
a 10 Hz b 30 Hz
c 50 Hz d 70 Hz [Ans. : c]

Q.22 In abrasive jet machining, what may be the size of the abrasive grains used ?
a 10 - 40 μm b 50 - 100 μm
c 100 - 150 μm d 200 - 300 μm [Ans. : a]

Q.23 What are the processes where abrasive jet machining can be used ?
a Cleaning b Cutting
c Deburring d All of the mentioned [Ans. : d]

Q.24 State whether the following statement is true or false.

“In Abrasive jet machining, commercial grades powders can be used for machining.”
a True b False [Ans. : b]

Q.25 In machining system of AJM, which of the following controls the relative motion between
work piece and nozzle ?
a Cam drives b Pantographs
c Trace mechanisms d All of the mentioned [Ans. : d]

Q.26 Masks, which are used to confine the jet stream location on work piece are made of,
which type of materials ?
a Copper b Glass
c Rubber d All of the mentioned [Ans. : d]

Q.27 In AJM, what is the mechanism of removal of material from the work piece ?
a Corrosion b Abrasion
c Electron transfer d Vaporization [Ans. : b]

Q.28 In AJM, abrasive jet from the nozzle follows, which type of path for a short distance ?
a Parallel b Inclined
c Perpendicular d None of the mentioned [Ans. : a]

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Q.29 Which of the following components, influence the material removal rate in abrasive jet
machining ?
a Nozzle b Carrier gas
c Abrasive grains d All of the mentioned [Ans. : d]

Q.30 In the following properties of nozzle, which of them does not influence the MRR ?
a Size b Wear
c Outside temperature d Distance from work piece [Ans. : c]

Q.31 In the following properties of abrasive grains, which of them changes rate of material
removal ?
a Size b Strength
c Shape d All of the mentioned [Ans. : d]

Q.32 As the abrasive flow rate increases, what happens to the volumetric removal rate ?
a Increases b Decreases
c Increase and then decrease d Decrease and then increase [Ans. : c]

Q.33 What is the value of abrasive grain flow rate in abrasive jet machining ?
a 0.1 - 2 g/min b 3 - 20 g/min
c 30 - 56 g/min d 68 - 85 g/min [Ans. : b]

Q.34 What must be the velocity of the carrier gas that carries the abrasive particles ?
a 10 - 50 m/sec b 50 - 150 m/sec
c 150 - 300 m/sec d 300 - 500 m/sec [Ans. : c]

Q.35 What is the value of carrier gas flow rate in abrasive jet machining ?
a 6 L/min b 17 L/min
c 28 L/min d 39 L/min [Ans. : c]

Q.36 Which of the following material/s cannot be used for making of nozzle in abrasive jet
machining ?
a Tungsten Carbide b Steel Alloy
c Sapphire d Synthetic Sapphire [Ans. : b]

Q.37 Which of the following values, does the diameter of the nozzle lies between ?
a 0.01 - 0.10 mm b 0.30 - 0.50 mm
c 0.70 - 0.90 mm d 1.10 - 1.50 mm [Ans. : b]

Q.38 What is the life of Tungsten Carbide material nozzle ?

a 1 - 8 hrs b 2 - 5 hrs

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Introduction and Mechanical Energy Based Processes

c 10 - 15 hrs d 25 - 40 hrs [Ans. : c]

Q.39 In AJM, what is the life of synthetic sapphire material nozzle ?

a 100 hrs b 300 hrs
c 500 hrs d 700 hrs [Ans. : b]

Q.40 What are the tolerance limit values in abrasive water jet machining ?
a ± 0.01 mm b ± 0.03 mm
c ± 0.05 mm d ± 0.07 mm [Ans. : c]

Q.41 In AJM, surface roughness value will vary between which values ?
a 0.01 - 0.10 μm b 0.15 - 1.5 μm
c 2.0 - 5.0 μm d 7.0 - 10.0 μm [Ans. : b]

Q.42 Which of the following, are the processes and applications in which abrasive jet
machining can be applied ?
a Drilling b Cutting
c Deburring d All of the mentioned [Ans. : d]

Q.43 Using abrasive jet machining, wire cleaning and insulation stripping take place without
affecting the conductor.
a True b False [Ans. : a]

Q.44 In abrasive jet machining, intricate shapes and holes are machined on which type of
materials ?
a Brittle b Thin
c Difficult to machine d All of the mentioned [Ans. : d]

Q.45 State whether the following statement is true or false, about abrasive jet machining.
“Using abrasive jet machining, micro deburring of hypodermic needles can take place.”
a True b False [Ans. : a]

Q.46 What are the type of materials that can be machined using abrasive jet machining ?
a Glass b Sapphire
c Quartz d All of the mentioned [Ans. : d]

Q.47 What is the amount of material utilizes when we machine parts using Abrasive jet
machining ?
a Very low b Low
c Medium d High [Ans. : d]

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Q.48 After how much time tool has to be changed in AJM ?

a 1 hr b 2 hrs
c 5 hrs d No tool change required [Ans. : d]

Q.49 By using abrasive jet machining, how much amount of hardening does the materials
experience ?
a No hardening b Very less hardening
c Average hardening d High hardening [Ans. : a]

Q.50 Which type of materials cannot be machined using abrasive jet machining ?
a Soft materials b Hard materials
c Difficult to machine materials d None of the mentioned [Ans. : a]

Q.51 Which of the following materials in abrasive jet machining can be a health hazard ?
a Abrasive grains b Air carrier
c Silica dust d None of the mentioned [Ans. : c]

Q.52 In AJM, air filters are used to remove which of the following ?
a Moisture b Oil
c Other dust particles d All of the mentioned [Ans. : d]

WATER JET MACHING

Q.53 What is the full form of WJM in advanced machining processes ?

a Water Jack Manufacturing b Water Jet Machining
c Water Jet Manufacturing d Water Jack Manufacturing [Ans. : b]

Q.54 What is the key element of water jet machining for material removal ?
a Tool Holder b Work piece
c Water jet d Power source [Ans. : c]

Q.55 What is the velocity of water jet stream in water jet machining ?
a 100 m/sec b 300 m/sec
c 700 m/sec d 900 m/sec [Ans. : d]

Q.56 Which of the following is not a part of machining system of water jet machining ?
a Transducer b Accumulator
c Jet cutting nozzle d Hydraulic pump [Ans. : a]

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Q.57 What is the general power rating of the hydraulic pump, used in WJM ?
a 10 kW b 20 kW
c 30 kW d 40 kW [Ans. : c]

Q.58 Which of the following are the components of intensifier present in water jet machining
system ?
a Piston b Plunger
c Limit switch d All of the mentioned [Ans. : d]

Q.59 Intensifier increases the pressure water by which of the following values ?
a 10 - 100 MPa b 100 - 200 MPa
c 200 - 400 MPa d 400 - 1000 MPa [Ans. : c]

Q.60 On which property of water, will the accumulator in water jet machining rely on ?
a Density b Compressibility
c Viscosity d Velocity [Ans. : b]

Q.61 What are the values of typical tube diameters in the machining system in WJM ?
a 0.1 to 1 mm b 1 to 6 mm
c 6 to 14 mm d 14 to 25 mm [Ans. : c]

Q.62 What is the expected life of the nozzles used in WJM ?

a 10 hrs b 20 hrs
c 100 hrs d 200 hrs [Ans. : d]

Q.63 Which of the following does not damage the nozzle used in Water jet machining ?
a Particles of dirt b Mineral deposits
c Water d All of the mentioned [Ans. : c]

Q.64 What are the uses of catcher in machining system of water jet machining ?
a Collecting dirt b Collection of debris
c Reduce noise levels d All of the mentioned [Ans. : d]

Q.65 Distance between which components, is the stand-off distance ?

a Nozzle-inlet and work piece top b Nozzle-outlet and work piece-top
c Nozzle-inlet and work piece-bottom d Nozzle-outlet and work piece-bottom [Ans. : b]

Q.66 What is the value of diameter of the jet cutting nozzle in WJM ?
a 0.01 - 0.1 mm b 0.1 - 0.3 mm
c 0.3 - 0.7 mm d 0.7 - 1.5 mm [Ans. : b]

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Q.67 What is the value of stand-off distance in Water jet machining ?

a 0.1 - 1 mm b 1 - 2 mm
c 2 - 6 mm d 6 - 14 mm [Ans. : c]

Q.68 What are the values of jet velocities in water jet machining ?
a 100 - 200 m/s b 200 - 500 m/s
c 500 - 1500 m/s d 1500 - 3000 m/s [Ans. : c]

Q.69 State whether the following statement is true or false.

“As the pump pressure increases, depth of cut decreases in Water jet machining.”
a True b False [Ans. : b]

Q.70 What is the value of material thickness of work piece in WJM ?

a 0.001 - 0.25 mm b 0.8 - 25 mm
c 50 - 100 mm d 100 - 500 mm [Ans. : b]

Q.71 What is the value of feed rate in Water Jet Machining ?

a 0.0001 - 0.025 m/min b 0.05 - 0.25 m/min
c 0.5 - 200 m/min d 200 - 500 m/min [Ans. : c]

Q.72 In WJM, what are the properties of jet fluid that affect the MRR ?
a Velocity b Flow rate
c Viscosity d All of the mentioned [Ans. : d]

Q.73 Which of the following property/ies of nozzle does not affect the material removal rate in
Water jet machining ?
a Material b Diameter
c Outside temperature d Stand-off distance [Ans. : c]

Q.74 In the following materials, Water jet machining can be used on which type of material ?
a Metals b Plastics
c Ceramics d All of the mentioned [Ans. : d]

Q.75 What are the processes and applications, where water jet machining can be used?
a Cutting b Drilling
c Deburring d All of the mentioned [Ans. : d]

Q.76 What is the tolerance limit range of thin materials in WJM ?

a ± 0.1 mm b ± 10 mm
c ± 25 mm d ± 50 mm [Ans. : c]

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Q.77 In cutting of rocks using water jet machining, which type of pressure is needed ?
a Low pressure b Medium pressure
c High pressure d None of the mentioned [Ans. : c]

Q.78 In deburring, which combination removes the material from non-metallic materials ?
a High pressure and low flow rate b High pressure and high flow rate
c Low pressure and low flow rate d Low pressure and high flow rate [Ans. : a]

Q.79 Which of the following materials has some drawbacks of cutting WJM ?
a Food b Rocks
c Fibre-reinforced plastics d None of the mentioned [Ans. : c]

Q.80 What is the accuracy level obtained when PCB’s are cut by WJM ?
a ± 0.05 mm b ± 0.13 mm
c ± 0.26 mm d ± 0.33 mm [Ans. : b]

Q.81 In WJM, surface treatment includes which type of processes ?

a Removing deposits b Removing chemicals
c Degreasing d All of the mentioned [Ans. : d]

Q.82 In how many directions, can the cutting takes place in water jet machining ?
a Uni-directional b Bi-directional
c Multi-directional d None of the mentioned [Ans. : c]

Q.83 In Water jet machining, cuts can be started at which place of workpiece ?
a From left b From right
c From middle d From any point [Ans. : d]

Q.84 State whether the following statement is true or false.

“To start the cuts in Water jet machining, pre-drilled holes are not necessary.”
a True b False [Ans. : b]

Q.85 Which of the following is not an advantage of water jet machining ?

a Burr produced is minimal b No Heat is produced
c Relatively low hourly rates d Environmentally safe [Ans. : c]

Q.86 In Water jet machining, tool need not require sharpening once the machining is done.
a True b False [Ans. : a]

Q.87 Which of the following secondary processes are eliminated in water jet machining ?
a Grinding of surface b Surface treatment
c Polishing of surface d All of the mentioned [Ans. : d]

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Q.88 How many parts are cut using water jet machining, on a single blank ?
a One part b Two parts
c Three parts d Multiple parts [Ans. : d]

Q.89 Which of the following is the disadvantage of water jet machining ?

a Narrow kerf width b Small diameter of nozzle
c Not suitable for mass production d Burr is minimal [Ans. : c]

ABRASIVE WATER JET MACHINING

Q.90 In advanced machining processes, what is the full form of AWJM ?

a Automated Water Jet Machining b Automated Water Jet Manufacturing
c Abrasive Water Jet Machining d Abrasive Water Jet Manufacturing [Ans. : c]

Q.91 What are all the types of materials, which can be machined using AWJM ?
a Glass b Ceramics
c Concrete d All of the mentioned [Ans. : d]

Q.92 When was abrasive water jet machining developed first ?

a 1942 b 1958
c 1974 d 1980 [Ans. : c]

Q.93 When compared to the conventional machining, how much times faster, is the abrasive
water jet machining ?
a 5 times b 10 times
c 15 times d 20 times [Ans. : b]

Q.94 What is the percentage of the abrasives and water in the mixture ?
a 20 % water and 80 % abrasives b 80 % water and 20 % abrasives
c 30 % water and 70 % abrasives d 70 % water and 30 % abrasives [Ans. : d]

Q.95 What are the materials used for abrasives in Abrasive water jet machining ?
a SiC b Corundum
c Glass beads d All of the mentioned [Ans. : d]

Q.96 In the machining system of AWJM, which one accelerates the abrasives to remove
material ?
a Water only b Water jet stream
c Feeder d None of the mentioned [Ans. : b]

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Q.97 The introduction of compressed air to the water jet enhances the deburring action.
a True b False [Ans. : a]

Q.98 What is the grain size of abrasive particles, which are often used for Abrasive water jet
machining ?
a 0.01 - 0.50 μm b 10 - 150 μm
c 200 - 500 μm d 500 - 1000 μm [Ans. : b]

Q.99 How is the material removed in abrasive water jet machining ?

a Vaporization b Electron transfer
c Corrosion d Erosion [Ans. : d]

Q.100 Which of the following is not the feed mechanism of the abrasives in AWJM ?
a Side feed b Cross feed
c Central feed d All of the mentioned [Ans. : b]

Q.101 In Abrasive water jet machining, how are the abrasives fed into the water jet stream ?
a Suspension b Injection
c All of the mentioned d None of the mentioned [Ans. : c]

Q.102 What is the use of delivery system in the machining system of AWJM ?
a To deliver colloidal solution b To pump water
c To fed abrasives d None of the mentioned [Ans. : b]

Q.103 Of the following components, which one does not come under the machining system of
AWJM ?
a Water delivery system b Transducer
c Cutting nozzles d Mixing chambers [Ans. : b]

Q.104 In abrasive water jet machining, intensifier is used to deliver which type of pressure ?
a Very low pressure b Low pressure
c Medium pressure d High pressure [Ans. : d]

Q.105 In mixing chamber of AWJM, which of the following are mixed ?

a Abrasives and colloidal solution b Abrasives and water jet
c Colloidal and water jet d None of the mentioned [Ans. : b]

Q.106 Of the following, which one is a type of suspension in AWJM ?

a Direct pumping b Indirect pumping
c Bypass pumping d All of the mentioned [Ans. : d]

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Q.107 In machining system of AWJM, mixing chamber is immediately followed by which of the
following component ?
a Focusing tube b Cutting nozzle
c Intensifier d Water delivery [Ans. : a]

Q.108 Which of the following energies are absorbed using the catchers in Abrasive water jet
machining ?
a Pressure energy b Kinetic energy of abrasives
c Residual energy d All of the mentioned [Ans. : c]

Q.109 Which of the following are different types of catchers used in AWJM ?
a Water basin type b Submerged steel balls type
c TiB2 type d All of the mentioned [Ans. : d]

Q.110 Which of the following is not a process parameter of abrasive water jet machining ?
a Frequency of vibration b Orifice diameter
c Pressure d Stand-off distance [Ans. : a]

Q.111 Which of the following come under the process parameters of the abrasive water jet
machining?
a Abrasive size b Machine impact angle
c Traverse speed d All of the mentioned [Ans. : d]

Q.112 What is the value of orifice diameter in abrasive water jet machining ?
a 0.01 - 0.03 mm b 0.03 - 0.09 mm
c 0.10 - 0.30 mm d 0.30 - 0.90 mm [Ans. : c]

Q.113 Of the following values, between which of them pressure value will range ?
a 1000 - 1500 bar b 1500 - 2500 bar
c 2500 - 4000 bar d 4000 - 10000 bar [Ans. : c]

Q.114 When compared to sand, how much effective is garnet as abrasive material in AWJM ?
a 20 % b 30 %
c 40 % d 50 % [Ans. : b]

Q.115 State whether the following statement is true or false about Abrasive water jet
machining.
“A material, whose material removal rate is higher, produces larger surface roughness.”
a True b False [Ans.: a]

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Q.116 Surface roughness depends on which of the following parameters in abrasive water jet
machining ?
a Work piece material b Grit size
c Abrasive type d All of the mentioned [Ans. : d]

Q.117 What is the value of focusing diameter in abrasive water jet machining ?
a 0.1 - 0.6 mm b 0.8 - 1.4 mm
c 1.6 - 2.8 mm d 3.2 - 5.2 mm [Ans. : b]

Q.118 Abrasive flow value in abrasive water jet machining will range between which of the
following values ?
a 0.01 - 0.1 kg/min b 0.1 - 1.0 kg/min
c 1.0 - 10 kg/min d 10 - 100 kg/min [Ans. : b]

Q.119 What is the value of stand-off distance in abrasive water jet machining?
a 1.0 - 2.0 mm b 2.0 - 4.0 mm
c 4.0 - 6.0 mm d 6.0 - 10.0 mm [Ans. : a]

Q.120 Impact angle in Abrasive water jet machining range between which of the following
values ?
a 0&#176 to 10&#176 b 10&#176 to 30&#176
c 30&#176 to 90&#176 d 90&#176 to 100&#176 [Ans. : c]

Q.121 Of the following values, between which values traverse speed will range ?
a 0.1 to 5 m/min b 5 to 100 m/min
c 100 to 500 m/min d 500 to 1000 m/min [Ans. : b]

Q.122 Depth of cut values in Abrasive water jet machining ranges between which values ?
a 0.01 to 2 mm b 2 to 250 mm
c 300 to 500 mm d 650 to 900 mm [Ans. : b]

Q.123 Who discovered USM ?

a Balamuth b Paul O Flawer
c Turing d Steve John [Ans. : a]

Q.124 What is the full form of USM in advanced machining process ?

a Ultrasound manufacturing b Ultrasonic machining
c UV spectrum manufacturing d Ultra sonar machining [Ans. : b]

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Q.125 USM removes materials using the tool.

a Perpendicularly rotating b Perpendicularly oscillating
c Axially oscillating d Inclined oscillating [Ans. : c]

Q.126 Which is softer material in USM ?

a Tool b Work piece
c Tool and work piece d None of the mentioned [Ans. : a]

Q.127 Frequency of tool’s oscillation in USM ranges between .

a 5-10 kHz b 10-15 kHz
c 18-20 kHz d 25-50 kHz [Ans. : c]

Q.128 Amplitude of oscillation of tool in USM ranges between .

a 0.1-10 μm b 10-40 μm
c 50-100 μm d 100-1000 μm [Ans. : b]

Q.129 In which year, discovery of USM took place ?

a 1910 b 1925
c 1943 d 1945 [Ans. : d]

Q.130 The machining system of USM contains which of the following components ?
a Magnetostrictor b Concentrator
c Tools and slurry d All of the mentioned [Ans. : d]

Q.131 In ultrasonic machining, magnetostrictor is energized at ultrasonic frequency.

a True b False [Ans. : a]

Q.132 Of the following scientists, who discovered magnetostrictor effect ?

a Balamuth b Steve O Flawer
c Joule d Turing [Ans. : c]

Q.133 In ultrasonic machining, magnetostrictor converts magnetic energy into which type of
energy ?
a Mechanical energy b Electrical energy
c Thermal energy d None of the mentioned [Ans. : a]

Q.134 What is the value of the amplitude obtained without mechanical amplifier ?
a 0.0001 - 0.001 μm b 0.001 - 0.1 μm
c 1 - 10 μm d 10 - 100 μm [Ans. : b]

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Q.135 What is the value of the amplitude obtained when we use mechanical amplifier ?
a 1 - 10 μm b 10 - 40 μm
c 40 - 50 μm d 50 - 100 μm [Ans. : c]

Q.136 In USM, tool tips must have low resistance and fatigue strength.
a True b False [Ans. : b]

Q.137 At what rate slurry is pumped through nozzle in USM ?

a 10 L/min b 25 L/min
c 50 L/min d 75 L/min [Ans. : b]

Q.138 By which of the following means, material is removed in USM ?

a Mechanical abrasion b Microchipping
c Cavitation d All of the mentioned [Ans. : d]

Q.139 What is the percentage of contribution of cavitation to the total material removed ?
a <5% b 5 - 10 %
c 10 - 20 % d 20 - 50 % [Ans. : a]

Q.140 In the following mechanisms, which one is dominant in material removal ?

a Hammering b Cavitation
c Microchipping d None of the mentioned [Ans. : a]

Q.141 When machining porous material, which type of mechanism is introduces ?

a Abrasion b Erosion
c Corrosion d Vaporization [Ans. : b]

Q.142 The rate of material removal depends on which of the following features ?
a Frequency b Static Pressure
c Machining area d All of the mentioned [Ans. : d]

Q.143 The machinability of USM depends on brittleness criterion.

a True b False [Ans. : a]

Q.144 Which of the following are the features of tool affecting MRR in USM ?
a Hardness b Wearability
c Accuracy d Mounting [Ans. : d]

Q.145 What is the machinability rate of glass by USM ?

a 25 % b 50 %
c 75 % d 100 % [Ans. : d]

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Q.146 What happens to MRR with increase in tool amplitude ?

a Increases b Decreases
c Remains same d None of the mentioned [Ans. : a]

Q.147 The vibration amplitude determines, which parameter of the abrasive particles ?
a Force b Torque
c Velocity d Pressure [Ans. : c]

Q.148 If splashing occurs, it will result in an increase of material removal rate in USM.
a True b False [Ans. : b]

Q.149 Amplitude of the oscillation ranges between which of the following values ?
a 0.01 - 0.04 mm b 0.04 - 0.08 mm
c 0.08 - 0.10 mm d 0.10 - 0.20 mm [Ans. : b]

Q.150 As the vibration frequency increases, what happens to material removal rate ?
a Decreases b Increases
c Increase and then decrease d Decrease and then increase [Ans. : c]

Q.151 Which of the following can be used as an abrasive carrying medium ?

a Water b Benzene
c Glycerol d All of the mentioned [Ans. : d]

Q.152 If there is an increase in viscosity of slurry, what happens to MRR ?

a Increases b Decreases
c Remains same d None of the mentioned [Ans. : b]

Q.153 How much percent of the abrasives are recommended in general for abrasive medium ?
a 10 - 15 % b 15 - 20 %
c 25 - 30 % d 30 - 35 % [Ans. : d]

Q.154 Machining rate can be affected by the ratio of hardness of tool to that of hardness of
work piece.
a True b False [Ans. : a]

Q.155 As the tool area increases, what happens to MRR ?

a Decreases b Increases
c Remains same d None of the mentioned [Ans. : a]

Q.156 When the static pressure of the feed is increases, what happens to MRR ?
a Increases b Decreases
c Increase up to a limiting condition d Decrease up to a limiting condition [Ans. : c]

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Q.157 Which of the following distribution factors, does not affect the machining parts ?
a Side wear of tool b Abrasive wear
c Accurate feed d Form error of tool [Ans. : c]

Q.158 Which one of the following factors affects the accuracy of parts ?
a Steady abrasive flow b Accurate feed
c Unsteady abrasive flow d Ultrasonic frequency [Ans. : c]

Q.159 State whether the statement is true or false.

“Hole oversize measures the difference between hole diameter measured at the bottom
surface, and the tool diameter.”
a True b False [Ans. : b]

Q.160 While machining W4C and glass, tool over cut size when compared to mean grain size
is ?
a Two times greater b Two times smaller
c Three times greater d Three times smaller [Ans. : a]

Q.161 While machining B4C, tool over cut size when compared to mean grain size is ?
a Two times greater b Two times smaller
c Three times greater d Three times smaller [Ans. : c]

Q.162 In the following USM accuracy levels are limited to which value ?
a ± 0.01 mm b ± 0.05 mm
c ± 0.10 mm d ± 0.50 mm [Ans. : b]

Q.163 Conicity resulting after machining by ultrasonic machining can be reduced by ?

a Direct injection of slurry b Tools having negative taper
c High static pressure d All of the mentioned [Ans. : d]

Q.164 Typical roundness error in graphite, resulted due to lateral vibrations is between ?
a 01 - 20 μm b 20 - 60 μm
c 60 - 100 μm d 100 - 150 μm [Ans. : b]

Q.165 Typical roundness error in glass, resulted due to lateral vibrations is between ?
a 01 - 20 μm b 20 - 40 μm
c 40 - 140 μm d 150 - 250 μm [Ans. : c]

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Q.166 Which of the following factors affect the surface finish of machined parts in ultrasonic
machining ?
a Amplitude b Material
c Tool surface d All of the mentioned [Ans. : d]

Q.167 What is value of surface finish achieved, when we use the abrasive of grit number 240 ?
a 0.01 - 0.08 μm b 0.08 - 0.13 μm
c 0.13 - 0.25 μm d 0.25 - 0.38 μm [Ans. : d]

Q.168 When the viscosity of liquid carrier is increased, the surface quality of the parts ?
a Increased b Decreased
c Remained same d None of the mentioned [Ans. : c]

Q.169 Ultrasonic Machining can be used for which of the following processes and
applications ?
a Drilling b Sinking and contouring
c Polishing d All of the mentioned [Ans. : d]

Q.170 What is the limit of surface area that is to be machined using USM ?
a <100 mm2 b <500 mm2
c <1000 mm2 d <1500 mm2 [Ans. : c]

Q.171 Drilling in ultrasonic machining is done, by which motion of the tool ?

a Only rotation b Only oscillation
c Oscillation and rotation d None of the mentioned [Ans. : c]

Q.172 In which of the following materials, rotary ultrasonic machining can be used to drill
holes through them ?
a Glass b Alumina
c Ferrite d All of the mentioned [Ans. : d]

Q.173 State whether the following statement is true or false.

“Rotary Ultrasonic Machining is the process in which, interrupted drilling of small-diameter
holes takes place.”
a True b False [Ans. : b]

Q.174 On which of the following features of cavity, will the penetration depth depend on ?
a Depth b Diameter
c Size d All of the mentioned. [Ans. : d]

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Q.175 What is the value of depth in ultrasonic sinking, after which, material removal becomes
difficult ?
a 1 to 2 mm b 2 to 5 mm
c 5 to 7 mm d 7 to 10 mm [Ans. : c]

Q.176 In production of EDM electrodes, typical ultrasonic speeds, in graphite ranges

between ?
a 0.01 - 0.10 cm/min b 0.10 - 0.25 cm/min
c 0.25 - 0.40 cm/min d 0.40 - 1.40 cm/min [Ans. : d]

Q.177 How much is the value of surface finished, achieved using ultrasonic polishing ?
a 0.1 μm b 0.3 μm
c 0.5 μm d 0.7 μm [Ans. : b]

Q.178 In micro-ultrasonic machining, which of the following component vibrates ?

a Tool b Work piece
c Feed pipe d All of the mentioned [Ans. : b]

Q.179 In micro-USM, using WC tool, what is the value of diameter can be achieved ?
a 1 μm b 3 μm
c 5 μm d 7 μm [Ans. : c]

Introduction and Mechanical Energy Based Processes ends ….

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 Phase Diagrams

Syllabus : Electric Discharge Machining (EDM) - Wire cut EDM - Working Principle-
equipments-Process Parameters-Surface Finish and MRR- electrode / Tool - Power and
control Circuits-Tool Wear - Dielectric - Flushing - Applications. Laser Beam machining
and drilling, (LBM), plasma, Arc machining (PAM) and Electron Beam Machining (EBM).
Principles - Equipment -Types - Beam control techniques - Applications.

Section No. Topic Name Page No.

2.1 Electric Discharge Machining (EDM) 2-2

2.2 Electrical Discharge Wire Cutting (EDWC) or Wire EDM 2 - 20

2.3 Laser Beam Machining (LBM) 2 - 24

2.4 Electron Beam Machining (EBM) 2 - 27

2.5 Plasma Arc Machining (PAM) 2 - 29

2.6 Two Marks Questions with Answers (Part - A) 2 - 31

2.7 Long Answered Questions (Part - B) 2 - 34

2.8 Multiple Choice Questions with Answers 2 - 35

 Thermal and Electrical Energy Based Processes

2.1 Electric Discharge Machining (EDM)

Definition
EDM is the controlled erosion of electrically conductive materials by the initiation of rapid
and repetitive spark discharge between the electrode tool (Cathode) and workpiece(Anode)
separated by a small gap of 0.01 to 0.05 mm, kept in a bath of dielectric medium.

Fig. 2.1 EDM Process

2.1.1 Equipment
The important elements of the EDM process equipment are,
1. Work-piece - All the conductive material can be worked by EDM.
2. Tool electrode - The EDM electrode is the tool that determines the shape of the
cavity to be produce.
3. Dielectric fluid - The EDM setup consists of tank in which the dielectric fluid is
filled. Electrode and workpiece submersed into the dielectric fluid.
4. Servo system - The servo system is commanded by signals from gap voltage sensor
system in the power supply and control the feed of electrode and workpiece to
precisely match the rate of material removal.
5. Power supply - The power supply is an important part of any EDM system. It
transform the alternating current from the main utility supply into the pulse direct
current (DC) required to produce the spark discharge at the machining gap.
6. The DC pulse generator is responsible for supplying pulses at a certain voltage and
current for specific amount of time.

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2.1.2 Dielectric Fluid

Functions of Dielectric Fluid
1. It acts as a spark conductor concentrating the energy to a very narrow region
2. It acts as a coolant for the workpiece and the tool
3. It acts as an insulating medium during the charging time of the sparking circuit in
order to discharge an effective spark for machining.
4. It acts as a coolant in quenching the spark and helps arching to be prevented.
5. It acts as a flushing medium for the disposal of the product of machining.

Fig. 2.2

Basic requirement of an ideal dielectric fluid

1. Should have a stable dielectric strength to be electrically nonconductive till the
required discharge voltage is built up and should thereafter break down in a very
short span of time.
2. It should have an optimum velocity, because a high viscosity of the dielectric results
in a poor flow of dielectric in the gap between the tool and workpiece. A low
viscosity dielectric is not able to carry the products of machining.

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 Thermal and Electrical Energy Based Processes

3. It should have high flash point to avoid any fire hazard.

4. It should be chemically stable at high temperatures and neutral, not to attack the
electrode, workpiece, the table or the container.
5. It should not emit any toxic vapors or unpleasant odour.
6. It should be cheap and easily available.

Notes : The various dielectric fluids used are hydrocarbon oils such as kerosene, silicon
oils, de-ionized water, transformer oil, white spirit, paraffin oil and polar liquids such as
aqueous solution of ethylene glycol.

• De-ionized water rarely used because it results in high electrode wear. But it enhances high
MRR and better cooling capacity.
• White spirit is used for machining small part with intricate details. Also it is used to
machine tungsten carbide.
• Choice of dielectric depends on
▪ Size of the workpiece
▪ Shape complexity
▪ Tolerance surface finish
▪ Material removal rate
• The dielectric is pumped and kept in circulation during the machining, so as to avoid non-
uniform machining and ensure surface quality which is intended.
2.1.3 Tool
• The purpose fi the tool in EDM process is to convert the electrical discharge pulse to the
workpiece to allow erosion of the workpiece at the required rate.

Desirable characteristics of the tool material

▪ High thermal conductivity
▪ High electrical conductivity
▪ High melting temperature
▪ Cheap and easily machinable
• The selection of tool material depends on
1. The wear ratio of the tool
It is the ratio of the loss of tool material is given time to the volume of metal removed
from the workpiece in the same time. The less the wear ratio, the better is the tool
material.

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 Thermal and Electrical Energy Based Processes

2. The hardness of the tool

Though material of any hardness may be used as an electrode the softer the tool
material the more will be the tool wear.
3. Tolerance of the workpiece
The required tolerance on the workpiece can only be obtained, when the tool wear
ratio is low.
4. Ease of shaping the tool electrode.
For precision manufacturing harder materials are selected which emposes difficulties
in shaping the tool.
5. The surface finish of the machined workpiece.
6. Total volume of the material to be removed.
7. Nature of the dielectric fluid.

2.1.4 Tool Materials

1. Metallic Materials
Electrolytic copper, Tellurium or Chromium Copper, Copper Tungsten, Brass,
tungsten, Steel, Zinc, Zinc Alloys, Tunsten Carbide and Aluminium.
2. Non-Metallic Materials – Graphite
3. Combination of metallic and non-metallic- Copper Graphite.
Copper and brass are the two commonly used tool materials since it satisfies all the
requirements but exhibits high wear rate.

Copper tungsten Less wear ratio, able to produce good surface

finish.
Difficulty in machining intricate shapes.

Tungsten carbide Difficult to machine to the required shape or

profile.

Graphite and copper graphite Easily machined and available in various

grades.
Drawback – its brittleness.

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• The advantages of graphite electrode.

1. It is not affected by thermal shocks.
2. It has relatively high melting point and also chemically stable.
3. Easily machinable by simple conventional methods.
4. Offers low cost of operation.
• Aluminium is used as an electrode because of its high thermal and electrical conductivity. It
also high machinability which enables it to be shaped to any profile.

2.1.5 Work Materials

• Work materials of any hardness value, which is electrically conductive can be processed by
EDM.
• On the reasons of economy, normally hard materials are machined by employing EDM
process. Refractory materials, hard carbides and hardenable steels also can be machined.

2.1.6 Servo Mechanism

• EDM machines are equipped with a servo control mechanism that automatically
maintains a constant gap of about the thickness of a human hair between the electrode
and the workpiece.
• It is important because, that there is no physical contact between the electrode and the
workpiece, otherwise arcing could damage the workpiece and break the wire in case of
wire EDM.
• The servomechanism advances the electrode into the workpiece as the operation
progresses and senses the work-wire spacing and controls it to maintain the proper arc
gap which is essential to a successful machining operation.

2.1.7 Electrode Feed Control

• Since, during operation both workpiece and electrode are eroded, the feed control must
maintain a movement of the electrode towards the workpiece at such a speed that the
working gap, and hence, the sparking voltage remains unaltered.

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Fig. 2.3

2.1.8 Spark Generator and Electrical Circuitry

• The power supply is an important part of EDM system. It transforms the AC into a pulsed
DC which is required to initiate and maintain the unidirectional spark discharges at the
machine gap.
• The functions of a spark generator in an EDM circuit are,
1. To supply the required voltage , for the machining discharge
2. To control the discharge duration
3. To have a control over the discharge current density
4. To control the discharge cycle
• Most EDM power supply circuits convert the input AC into DC power by employing
conventional solid state rectifier. In all EDM circuits, a capacitor is used for storing the
electric charge before the discharge takes place across the gap.
• To achieve the different functions, different power supply circuits are used. They are
1. Relaxation Circuit (RC) or Resistance Capacitance Circuit or RC circuit.
2. Rotary impulse generators
3. Controlled pulse circuit.

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2.1.8.1 Relaxation Circuit or Resistance - Capacitance Circuit

(g) Vacuum tube (two power source) (h) Transisted pulsed circuit

Fig. 2.4 Types of power supply

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• It is one of the oldest and simplest generator to initiate the spark. This generator supplies
current to a condenser, the discharge from which produces the spark. The R-C circuit
operates on the principle of self-oscillation.
• When the power supply is switched on, the condenser charges through the resistance R.
The voltage across the gap V varies with time according to the relation
–t/re
V = Vs (1 – e )
Where,
Vs = The source voltage or supply voltage
T = The time starting at the instant Vs is applied
• First the value of V keeps on rising till it approaches the voltage which is sufficient to
breakdown the dielectric medium. The voltage at this point is termed as discharge
voltage.
• The discharge time is much smaller than the charging time.
• The spark frequency (γ) is approximately given by the following equation.
1 1
 = tC = Vs
RC Log
Vs – Vd

Fig. 2.5 Basic circuit of spark generator

Fig. 2.6 RC circuit

• Where, tc is the charging time which is the time required for the gap voltage to reach a
value Vd.

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• The pulse generator circuit can produce high energy sparks whose frequency ranges
from 3000 to 10000 per second.
• In this circuit metal removal rate largely depends on high amperage and capacitance.
• An increase in supply voltage means increase in energy liberated per pulse. But this also
results in longer charging cycle and lowering of process efficiency.
• The rate of charging of the condenser is influenced by the capacitance (C) and
resistance(R).
• This type of circuit is simple, rugged, cheap and reliable in construction. It is best suited
for large amount of metal removal rate where critical surface finish is not desired.

2.1.8.2 Rotary Impulse Generator

• It supplies the voltage wave form based on the principles as in the case of DC
generators. The rotary impulse generator eliminates the disadvantages of the relaxation
circuit. This generator is used for increasing MRR.
• This circuit consists of a rectifier to convert the AC into DC and a pulsar to initiate DC
pulses or unipolar pulses.
• The capacitor in this rotary impulse generator is charged through a diode during the first
half cycle of the AC input. In the next half cycle, the sum of the voltages generated by
the generator and the charged capacitor is applied to the work-tool gap.
• The operating frequency of the generator depends on the motor speed. This generator
circuit produces high MRR but poor surface finish.
2.1.8.3 Controlled Pulse Generator
• These generators consists of electronic switching units which allow the current to pass
periodically and to effectively control the parameters of the machining.
• This generator circuit also prevents current flow when a short circuit is developed. To
achieve this a transistor is used as a switching device.
• A high frequency and a maximum amperage at that frequency results in optimum metal
removal rate, with better surface finish. But a high frequency and low amperage setting
results in excellent surface finish. Roughing application can employ low frequency
discharges.
Notes : High frequency and maximum amperage gives better surface finish,
whereas high frequency and low amperage gives poor surface finish.

• In the controlled pulse generator circuit, current flows through the gap from the
capacitor during sparking.

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• The transistor attached in the circuit behaves as an infinite resistance, by getting biased.
When the current in the gap ceases, the conductivity of the tube increases, allowing the
flow of current to charge the capacitor for the next cycle.
• An oscillator if employed in the circuit will help to control the biasing and allow the
current to flow cyclically with an imposed frequency and increased stability.

Fig. 2.7 Slenoid controlled EDM

• Advantages of pulse controlled generators.

1. Tool wear is greatly reduced.
2. Better surface finish
3. No. of spark per second produced is high which reduces the machining time.

2.1.9 Working Principle of EDM

• The EDM process involves the removal of work material by finite discrete periodic
sparks between tool and the conductive work material separated by a thin film of
dielectric medium.
• When two electrodes connected to a DC power source are separated by a very small gap,
spark occurs between the two electrodes at the point of closest contact.
• Workpiece is connected to a positive terminal of the DC power supply and negative is
connected to a tool.
• In EDM tool shaped to the mirror image of the cavity to be produced.
• The tool and the work are kept immersed in a dielectric medium to promote the
effectiveness of the process.

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• When the voltage across the gap becomes sufficiently larger (more than 250 V) the high
power spark is produced. So, the dielectric breaks down and electrons are emitted from
the cathode (Tool) and the gap is ionized.
• This spark occurs in an interval of 10 to 30 micro seconds and with a current density of
15 - 500 A per mm2 approximately. So thousands of spark discharge occur per second
across the gap between the tool and the work. Which results in increasing temperature of
about 10000° C
• At this high temperature, work piece metal is melted, eroded and some of it is vaporized.
In this way the metal is removed from the work piece.
• The removed fine material particles are carried away by dielectric fluid circulated
around it.
• Particles eroded from the electrodes are known as Debris.
• When the two electrodes are of the same material, the positive terminal is eroded at a
faster rate than the negative one.

2.1.10 Mechanism of Metal Removal

• When a suitable voltage is applied between the work and the tool, an electrostatic field
of sufficient strength is established and due to this cold emission of electrons starts from
the cathode.
• These electrons from the cathode accelerate towards the anode. These electrons while
travelling towards the anode collide with the molecules of the dielectric fluid breaking
them into electrons and positive ions.
• The electrons so produced also accelerate towards the anode and also dislodge other
electrons from the dielectric medium during their travel.
• This process leads to the formation of a narrow column of ionized dielectric molecules
between the tool and workpiece.
• This ionized column of ions, have high conductivity, is the spark. This spark occurs at
the place of closest contact between the tool and workpiece surface, producing very high
temperature on the electrodes.
• This high temperature melts and vaporizes the positive electrode at the spot of spark
formation and the compression shock wave generated evacuate the molten metal by
mechanical blast, thus removing material.
• When the material is thus removed the spark gap at that particular spot increases and the
cycle is repeated at the place of next shortest gap.

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Fig. 2.8

• When the above process is taking place in the equipment, yet another phenomenon
occurs in the electrical circuit.
• When the supply voltage is given to the circuit, since the dielectric as it is, is a non-
conductor does not allow the current to flow through the gap. So a major part of the
applied voltage is stored in the condenser for further recharge.
• A minor portion of the applied voltage causes the cold emission of electrons from the
cathode.
• When dielectric medium is fully ionized it becomes a conductor and the entire stored
voltage in the capacitor is discharged from the cathode to anode which removes the
material.

2.1.11 Material Removal Rate

• The amount of material removed in a single discharge can be determined by considering
the diameter of the crater and the depth to which melting temperature is reached.
• Assumptions considered for the theoretical calculation of MRR are
▪ The properties of the electrode material do not change with the increase of
temperature.
▪ The rate of heat input is a constant throughout the discharge period.
▪ The vaporization of the electrode material is neglected.
▪ The spark is a uniform circular column heat source and the diameter of the column is
also a constant.
▪ The regions other than the heat source is insulated.
• MRR increases with an increase in discharge duration for different spark energies, but
up to a certain limit and then drops to zero. It is also observed that the MRR is
maximum when the pressure is below atmospheric.
• The MRR is also strongly influenced by the circulation of dielectric fluid, without a
forced circulation, the wear particles melt and reunite with the electrode.

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Fig. 2.9 Graphical representation of various process parameters

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• The MRR is proportional to the working current. (Working current is the volume of
metal removed per unit time per ampere). As the current increases, the energy of spark
increases and hence the MRR.
• A higher pulse energy increases MRR but results in a bigger size of broken off or
machined particles.
• For a particular electrical parameter, there is an optimum machining at which the MRR
is high, lower the electrical conductivity of a work material, lower will be the MRR.
• The viscosity of the dielectric medium also influences the MRR. Lower is the viscosity
of the dielectric, lesser will be the amount of eroded particle carried away which would
affect the MRR.
• The metal removal rate increases with the decrease in the resistance for a particular
value of capacitance. However, the resistance is decreased below a particular value
would in arching and damage the work.

2.1.12 Expression for Material Removal Rate (MRR)

• The MRR in EDM is basically a function of the current and the melting point of the
workpiece material, although other process variables also have an effect. The following
approximate empirical relationship
4
can be used as a guide to estimate the MRR in EDM.
MRR = 4  –1.23 3
10 I.T W mm
I = Current in ampere
TW = Melting point of the workpiece in °C

2.1.13 Tool Electrode Wear

• During the EDM operation not only the work material (Anode) is eroded but also the
cathode due to sparking.
• The wear ratio is the ratio of the materials removed from the work materials to
material removed from the tool
Materials removed from the work materials
Wear ratio =
Material removed from the tool
• Normally electrode wear at the end of corner or at all the sides. The electrode wear is
basically function of polarity, thermal conductivity, melting point of electrode, duration
and intensity of spark discharges and the type of work material used in connection with
the tool material.
• The knowledge of the tool wear is important while designing the tool electrode and the
selection of tool for a particular application.

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Fig. 2.10

• The wear rate of the electrode wt, can be estimated from the empirical equation:
11 –2.38
wt = 1.1  10 I.Tt mm3 / min.
where, Tt is the melting point of electrode material
The wear ratio of the workpiece to electrode, R can be estimated from the expression
–2.38
R = 2.25 Tr
where, Tr is the ratio of workpiece to electrode melting point.

2.1.14 Accuracy and Surface Finish

• The accuracy and the surface finish in EDM is depends on the diameter and depth of the
crater formed due to the spark. If the size of the crater is large, then the surface finish
obtained is rough.
• The greatest factor responsible for inaccuracy in the EDM process is the formation of
side sparks between the tool surface and the machined work piece. The side sparks
remove extra material from the machined surface and enlarges the cavity or hole.
• Higher value of capacitance leads to greater pulse energy and hence bigger particles of
material removal.
• If the machining area is more, larger is the inaccuracy.
• Lesser the tool wear ratio greater will be the inaccuracy.
• Increase of pulse energy increase in the working voltage and leads to poor or rough
surface finish.
• Forced circulation of the dielectric fluid results in improved surface finish than without
forced circulation.

2.1.15 Flushing
• The circulation of dielectric fluid between the electrode and the workpiece is called
flushing. Flushing is a vital for process efficiency and product quality.

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• The effective flushing removes wastes products from the gap and increases MRR
whereas the bad flushing results in low MRR and poor surface finish.
• The good flushing system is one that shoots the dielectric to the place where the
sparking occurs. It is observed that flushing in blind cavities is difficult.
• So, flushing does not perform well in blind cavities.
• Various methods of flushing are,
▪ Suction through electrode ▪ Suction through workpiece
▪ Pressure through electrode ▪ Pressure through workpiece
▪ Jet flushing ▪ Periodic cycling of electrode

i) Sunction through electrode iv) Pressure through electrodes

ii) Sunction through workpiece v) Pressure through workpiece

iii) Flushing vi) Periodic cycling of electrode

Fig. 2.11

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2.1.16 Advantages
1. Any conductive materials of any hardness, toughness or brittleness can be machined.
2. Tool material property is not a constraint to restrict the machining.
3. No cutting forces is encountered since there is no contact between tool and
workpiece.
4. Thin sections also can be machined.
5. Complicated geometrical forms can be easily reproduced.
6. High accuracy is possible.
7. It is a burrless process.
8. Materials can be machined even in the heat treated condition.
9. Surface finish obtained is good.
10. More suitable for producing surfaces that are to be used for wear resistance which can
contain lubricant.

2.1.17 Disadvantages
1. Low material removal rate (MRR)
2. Thermal stress may develop due to intense heat.
3. Power required is very high.
4. Possibility of surface cracking is encountered in some materials
5. Difficult to produce soft corners.

2.1.18 Limitations
1. Only electrically conductive material can be machined.
2. Tool wear affect the accuracy and surface finish.
3. Produces heat affected zone(HAZ) in the work material.
4. High specific energy consumption.

2.1.19 Applications
1. Chiefly employed for the manufacture and reconditioning of press tools, forging dies,
extrusion dies and moulds for the injection moulding.
2. Any intricate shapes or profiles on alloy steel, tungsten carbide dies can be produced
with fine details.
3. Blind complex cavities micro holes for nozzles and fuel injectors through cutting of
non-circular holes and narrow slots can be produced.
4. Used for machining fragile work pieces.

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5. Fine slits can be made by using a wire electrode.

6. Fine cutting can be obtained using thread shaped electrode.
7. Hole as small as 0.1 mm in diameter can be drilled.
8. Embossing and engraving operations is also possible using this process.
9. Stamping and wire drawing dies can be produced by this process.
10. Punches and forming dies are manufactured by this process.
11. Internal threads and internal helical gears can be cut in hardened materials by
employing rotary spindle and suitable attachments.
12. Curved hole drilling and deep trepan drilling can also be done by this EDM process.
13. Die-sinking, cutting, slicing using a rotary disc or ribbon, external and internal form
grinding are some more operations that can be performed using EDM process.

Fig. 2.12 Fine cutting with thread

shaped electrode Fig. 2.13 Drilling of micro holes

Fig. 2.14 Thread cutting Fig. 2.15 Curved hole drilling

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Fig. 2.17 Deep trepan drilling with

injection of dielectric but without
Fig. 2.16 Hellical profile drilling electrode rotation

• Factors to be considered while selecting EDM machine tool are tolerance and surface
finish, power requirement, material removal rate, cost, efficiency, tooling and fixtures, tool
consumption, safety, work material, and shape feature.

2.2 Electrical Discharge Wire Cutting (EDWC) or Wire EDM

• The EDWC process uses the same principle of EDM process for material removal.
• The EDWC process differs from the EDM process in the sense that it uses a thin wire to
spark erode the workpiece in a complex 2D or 3D profile.
• The prominent feature of a moving wire is that, any complicated profile can be easily
machined without using a forming electrode.
• This EDWC process can also be called as travelling wire EDM or Wire EDM.

Definition
• The EDWC is a material removing process in which a thin wire is used along with a
stream of dielectric fluid for facilitating spark erosion.

2.2.1 Equipment
This process consists of the following elements,

1. Wire driving system 2. Positioning system

3. Power supply system 4. Dielectric system

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2.2.1.1 Wire Driving System

• The EDWC removes material by using a wire electrode which is moved along the
required profile or shape. The function of wire driving system is to continuously feed
the wire under constant tension to the work area.
• The tensioning of the wire avoids problems that occur during machining such as taper,
machining streaks, wire breaks, vibration markings.
• The wire in this process is fed from a spool, through several stages of preparation
system which ensures wire straightness.
• Before the wire is passed through the workpiece, it is guided by set of rollers made of
sapphire or diamond. But before being collected by the take up spool, it passes through a
series of tensioning rollers.
• Some machine uses devices for wire drawing and annealing to enable direct use of the
available commercial grade wires.
• When the wire passes through the workpiece, a major portion of the spark discharges
occur at the leading surface of the wire, which results in the deformation of the wire
cross section and so the wires is discarded after single use.

Notes : Copper, brass, tungsten and molybdenum are the materials used as wire
electrode.

• The diameter of the wire electrode ranges from 0.076 mm to 0.3 mm. The normally used
size of the electrode wire is 0.2 mm. The size is decided on the basis of the desired kerf
width.
• Kerf width is one of the important performance measures in WEDM. Kerf width is the
measure of the amount of the material that is wasted during machining. It determines the
dimensional accuracy of the finishing part.

2.2.1.2 Positioning System

• The EDWC positioning system consists of a CNC table which may be two axis or multi
axis, depending on the shape of the profile.
• The spark gap is maintained at the required value between the workpiece and the
wire electrode by connecting the positioning system to adaptive control mode.
• This mode enables the positioning system to avoid short circuiting, if in case any
machined material comes between wire electrode and the workpiece.

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2.2.1.3 Power Supply System

• There are differences between the conventional EDM and the EDWC power supply
system. The most differences are the frequency of the pulse and the current.
• To obtain a smooth surface finish, high frequency pulses are used in EDWC.
• Since the diameter of the wire used is small, current rating less than 20 Amps is only
supplied.

2.2.1.4 Dielectric System

• Deionized water is normally used as the dielectric fluid because of its low viscosity to
enter into the smaller gap, high cooling rate, high MRR and no fire hazard.
• The dielectric fluid is delivered through a nozzle to the machining area coaxial with the
wire. The de-ionized water is used once is filtered with filter paper and reused again.

2.2.2 Working Principle of EWDC

Fig. 2.18

• EDWC uses the thermal energy produced by the spark for removing the material. The
work material is connected to the positive terminal and the wire electrode to the
negative terminal of the high frequency pulses of DC power supply, which are separated
by the spark gap.
• The spark gap is fed with the supply of dielectric fluid.
• When the power supply is switched on spark appears in the gap and the work material is
machined by the intense heat which melts and vaporizes it.

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• The wire is continuously fed from spool through the guiding rolls and taken up by the
take up rolls.
• The machine table is moved along with the workpiece along the profile in which it need
to be machined.

2.2.3 Material Removal Rate

• The MRR for wire EDM can be obtained from the following expression,
MRR = Vf h.b
Vf = Feed rate of the wire into workpiece in mm/min.
h = Workpiece thickness or height in mm. and, the kerf is denoted as dw+2s

dw = Wire diameter in mm.

S = Gap between wire and workpiece during machining in mm.

2.2.4 Advantages
1. No fabrication of electrode is required.
2. No cutting force are encountered.
3. Can machine any hard material.
4. Automation is possible.
5. Electrode wear is negligible.
6. Machined surfaces are smooth.
7. Extremely high tolerances can be achieved.
8. Any profile or shape can be obtained through this process.

2.2.5 Disadvantages
1. High capital cost.
2. Formation of thin recast layer
3. Slow cutting rate
4. Applicable only in small parts.
5. Wire electrode cannot be reused which calls for high cost of electrode.

2.2.6 Applications
1. Best suited for the production of extrusion dies, Blanking dies and punches. Press
tools and sintered compacting dies.

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2. Can be used for shallow cutting, finishing operations and micro-drilling of non-
conducting materials.
3. Thick sections of 200mm can be used machined.
4. The machining of hard press-stamping dies can be easily done.
5. Even heat treated materials can also be processed by this process.
6. Stator, core-stamping dies are machined by wire-EDM.
7. The powder compaction dies which are more thicker than normal dies, with high
aspect ratios can be machined easily.
8. Even EDM electrodes can be made by this EDWC process.
9. Fabrication of grinding wheel form tools, profile gauges and templates are possible.
10. Large quantities of parts can be cut simultaneously by arranging them into a stack.

2.2.7 Difference between EDM and Wire Cut EDM

S. No Wire cut EDM EDM (Die sinking)

1. Thin wire is used as a tool Shaped tool is used. (Mirror image of the
workpiece)

2. Very thin wire made of brass or Expensive alloy of silver and tungsten are
molybdenum is used as the electrode (tool). used as the electrode (tool) which are
traditionally made by cutting and grinding.

3. The whole workpiece is not submerged in The whole workpiece is submerged in

dielectric medium. Instead, the working dielectric medium
zone alone is supplied with a co-axial jet of
dielectric medium

4. It is easy to machine complex two It is difficult to cut complex two dimensional

dimensional profiles. profiles.

2.3 Laser Beam Machining (LBM)

Laser is the term applied for phenomenon of amplification of light by stimulated radiation
emission.

2.3.1 Construction
• Fig. 2.19 shows the setup of laser beam machining, which consists of a stimulating light
source (Xenon flash lamp) and a laser rod.

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Fig. 2.19 : Laser beam machining

• Laser rod or laser tube consists of a pair of mirrors, which are placed at each end of a
tube.
• Setup also consists of a flash tube /lamp (energy source), laser, power source, focussing
source (lens) and cooling system.
• The whole setup is fitted inside an enclosure which has highly reflective surface inside
it.
• The laser used in the process may be solid, liquid or gaseous type. The solid type carries
reflective coatings at their ends and gaseous type produces continuous laser beams and
is suitable for welding and cutting operations. Most commonly used laser is Ruby.

2.3.2 Working
• In operation, the optical energy (light) radiated from the flash lamp is focussed on the
laser rod (tube), from where it is reflected with the help of mirrors and accelerated in its
path.
• The reflected light is emitted in the form of a slightly divergent beam.
• A lens is placed in the path of this beam of light which converges and focuses the light
beam on the component to be machined (workpiece).
• This impact of laser beam on the component melts the work material and due to this it
vaporises. Hence it is also called as thermal cutting process.

2.3.3 Laser Machining System

Fig. 2.20 shows the different types of laser machining systems.

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Fig. 2.20 : Laser machining systems

• Fig. 2.20 (a) is a spiral flash lamp in which a ruby rod is kept inside the lamp.
• Fig. 2.20 (b) shows a straight flash lamp and cylindrical mirror with elliptical cross-
section.
• Fig. 2.20 (c) is another laser machining system in which circular reflecting cylinder is
shown.
• Fig. 2.20 (d) shows four flash lamps arranged around the ruby rod.

2.3.4 Advantages of LBM

• In LBM process there is no direct contact between the tool and workpiece, hence tool
wear does not exist.
• Easy machining of brittle, non-metallic and hard materials.
• Machining can be done in any environment.
• Extremely small holes can be drilled easily.
• Refractory materials can be easily worked.
• Also used for welding of dissimilar metals.
2.3.5 Disadvantages of LBM
• LBM is applicable only for thin sections and where a small quantity of material is
removed.
• Holes drilled may have a slight taper formation, hence not suitable for large holes.
• Control of hole size is difficult.
• Safety precautions and procedures are to be followed.
• Durability and reliability of the system is limited.
• Limited life of flash lamp leads high operational cost.
• Initial cost and operating cost of system is quite high.
• Due to low production rate, efficiency of the system is low.
• Highly skilled operators are required.

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2.3.6 Applications of LBM :

• LBM is mainly used for trimming of sheet metal, carbon resistors and plastic parts.
• It is used for drilling small holes in materials like tungsten, ceramics which are very
hard.
• Cutting complicated profiles on thin films for making ICs (Integrated Circuits),
engraving patterns on thin films LBM is used.
• LBM is also suitable for dynamic balancing of precise rotating components like
watches.

2.4 Electron Beam Machining (EBM)

2.4.1 Principle :
• EBM process is used for machining of materials using high velocity beam of electrons.
The component to be machined (workpiece) is held in vacuum chamber and beam of
electrons is focused on to it magnetically.

Fig. 2.21 : Electron beam machining

• When electrons strike the workpiece their kinetic energy is converted into heat energy
and raises the temperature of workpiece. Due to high temperature, a small amount of

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workpiece material vaporises that means there is removal of metal from the workpiece.
2.4.2 Construction
• Fig. 2.21 shows the set up for Electron Beam Machining. The complete setup is
enclosed in a vacuum chamber having vacuum of order 10–5 mm of Hg.
• The vacuum chamber carries a door, through which the component to be machined
(workpiece) is placed on the table. After placing the component the door is sealed.
• The electron gun which is the main cause of emission of electrons consists of three main
parts :
(a) Tungsten filament (b) Grid cup (c) Anode.
• Tungsten filament acts as a cathode, as it is connected to negative terminal of D.C.
supply and positive terminal is connected to anode as shown in Fig. 2.21.

2.4.3 Working
• As the current supply starts, the filament wire is heated to a temperature upto 2500C in
the vacuum. Due to this, electrons are emitted by filament, which is directed by the grid
cup to travel downward.
• A potential difference of 50-150 kV is maintained between anode and filament. The
velocity of electron passing through anode is 2/3 of light.
• This high velocity electron stream after passing through anode passes through tungsten
diaphragm and then through the electromagnetic focussing coil.
• After passing through focussing coil (focussing lens) it precisely focus on the desired
area of the component.
• The workpiece is kept on the table which can be traversed as per the requirement.
• When the high velocity beam of electrons impact on the workpiece, its kinetic energy is
converted into heat energy.
• Due to high temperature, generated (heat) material from the workpiece is removed by
vaporisation.
• Melting and vaporising of the metal takes only a fraction of second and turning off of
the beam is necessary to conduct away the heat from the workpiece.
Need for vacuum :
• The electron beam should not collide with the molecules of gas and should not scatter.
• Electrons can travel from cathode to anode easily.
• There should be no loss of heat from cathode.
• To maintain high velocity of electron beam i.e. 2/3 of light.

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2.4.4 Advantages of EBM

• Accurate and precise holes can be machined.
• It is a quicker process i.e. 1 hole in 1 second.
• Small diameter, narrow slots can be easily machined.
• It can machine any material i.e. metal or non-metal.
• Close dimension tolerances can be machined, as there is no tool wear as in case of
EDM.
• There is no direct contact between tool and workpiece, hence damage of workpiece
surface is avoided.
• It is a good technique for micro-machining.

2.4.5 Disadvantages of EBM

• Perfectly cylindrical deep holes can not be produced.
• High power consumption.
• As the process takes place in vacuum chamber and size of the chamber is limited,
workpiece size is also limited.
• MRR is low.
• Initial investment is high.
• Highly skilled operator is required for the operation.

2.4.6 Applications of EBM

• EBM is used for producing precise holes in wire drawing dies.
• Used for machining operations like cutting, drilling or milling on varieties of materials,
irrespective of hardness.
• Also suitable for micro-drilling operations (upto 0.002 mm) for thin orifices, injector
nozzles for diesel engines.
• Also used for synthetic jewels drilling in watch industry.
2.5 Plasma Arc Machining (PAM)
The gases have property that when they are heated to temperatures above 5500 C they are
partially ionised and they exist in the form of a mixture of positively charged ions, neutral
atoms and free electrons. This mixture is called as Plasma. Central part temperature of plasma
is upto 11000 C to 28000 C and at that temperature the gas is completely ionised.

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Fig. 2.22 : Principle of plasma arc machining

2.5.1 Construction
• Fig. 2.22 shows the general set-up for plasma arc machining or many times called as
Plasma Arc Cutting.
• In this the Plasma-arc cutting torch carries an electrode which is generally made up of
tungsten fitted in a small chamber.
• This tungsten electrode is connected to the negative terminal of a d.c. supply, hence acts
as a cathode whereas positive terminal is connected to nozzle formed near the bottom of
the chamber, hence acts as anode.
• Near the torch, small area is provided for supply of gas into the chamber. Also, while
operation, electrode and nozzle should remain cool hence, water circulation is provided
around the torch.

2.5.2 Working
• In PAM, as per Fig. 2.22 high velocity jet of high temperature ionised gas (plasma) is
directed on the component (workpiece) surface with the help of a plasma cutting torch.
• This high velocity jet melts the metal of the workpiece and molten metal is thrown away
from its path.
• The workpiece is heated due to continuous attack of electrons, which transfers heat
energy of ionised gas to the work material.

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2.5.3 Advantages of PAM

• PAM is a quicker process.
• A very high temperature is generated for machining.
• PAM is used to cut any metal.
• There is no contact between the workpiece and tool.
• Good surface finish and accuracy upto 5-10 microns can be obtained.
3
• High cutting rate upto 250-1700 m/min is available. (Gas flow rate is upto 2-10 m /hr).

2.5.4 Disadvantages of PAM

• As the temperature generated is very high, more precautions are required for the
operator.
• Due to high temperature, work surface may undergo some metallurgical changes.
• Operator also requires protection from shielding and noise.
• Initial cost of the equipment is very high.

2.5.5 Applications of PAM

• PAM is used for profile cutting of alloy steel, stainless steel, aluminium and its alloys.
• PAM is used for turning and milling of difficult to machine materials.
• Also used for removing gates and risers from a casting.
• As PAM is also used under water, it is mostly used in shipyards, chemical industries and
many times in nuclear plant also.
• PAM is used for cutting of hot extrusions.

2.6 Two Marks Questions with Answers (Part - A)

What is the purpose of dielectric in EDM ?
Ans. : Dielectric is an important parameter in EDM and plays a crucial role in determining
high Material Removal Rate (MRR) and surface finish during operation.
The dielectric fluid behave as a medium which controls the electrical discharge and absorb
heat during process.
List the applications of EDM.
Ans. :
• Die making : Dies are tools used to cut or shape materials into a solid product.
• Mold Making.
• Small Hole Drilling

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Q.3 What are the properties required for dielectric fluid for EDM ?
(Section 2.1.2 (Basic requirement of an ideal dielectric Fluid))
Q.4 List out the limitations of EDM ? (Section 2.1.18)
Q.5 Give the product applications of EDM ? (Section 2.1.18)
Q.6 List the advantages of EDM ? (Section 2.1.16)
Q.7 What is the function of servocontrol system in EDM ? (Section 2.1.6)
Q.8 What are the types of tool materials used in EDM ? (Section 2.1.4)
Q.9 What are the types of power generator circuits used in EDM ? (Fig. 2.4)
Q.10 What do you mean by recast layer with reference to the EDM ?
Ans. : The sparks produced during the EDM process melt the metal's surface, which then
undergo ultra-rapid quenching. A layer forms on the workpiece surface defined as a recast
layer after solidification
Q.11 What are the functions of adaptive control used for EDM ?
Ans. : The purpose of the adaptive control in an EDM sinker is to read the conditions of the
EDM spark and translate these conditions into digital signals that are fed into the machine's
controller. The controller translates these signals, determines the efficiency of the EDM cut
and makes adjustments accordingly.
Q.12 What are the ways of gap-flushing used in EDM ? (Fig. 2.11)
Q.13 Name any four electrode materials used in EDM process. (Section 2.1.4)
Q.14 What are the functions of dielectric fluid used in Electric Discharge Machining ?
(Section 2.1.2)
Q.15 Sketch the relaxation circuit of EDM. (Section 2.1.8.1)
Q.16 State the principle of EDM. (Section 2.1 (Definition))
Q.17 Name some of the most commonly used dielectric fluids in EDM.
Ans. : So Many different fluids are used as dielectric fluids. Most of them are
hydrocarbon fluids, silicone-based oils and de-ionized water, kerosene oil and water with
glycol.
Q.18 State the difference between wire cut EDM and EDM. (Section 2.2.7)
Q.19 What is the principle of operation of wire cut EDM process ? (Section 2.2)
Q.20 List out the applications of wire cut EDM process. (Section 2.2.6)
Q.21 What is the purpose of vacuum chamber in EBM process ?
Ans. : Vacuums must be used to reduce contamination, and minimize electron collisions
with air molecules. Because work must be done in a vacuum, EBM is best suited for small
parts. The interaction of the electron beam with the work piece produces hazardous x-rays,
and only highly trained personnel should use EBM equipment.

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Q.22 Define electron beam.

Ans. : Electron beam, stream of electrons generated by heat (thermionic emission),
bombardment of charged atoms or particles (secondary electron emission), or strong electric
fields (field emission). Electrons may be collimated by holes and slits, and, because they are
electrically charged, they may be deflected, focused, and energized by electric and magnetic
fields
Q.23 In EBM, why is a high vacuum created in the apparatus?
Ans. : The entire process occurs in a vacuum chamber because a collision between an
electron and an air molecule causes the electrons to scatter and thus loose their energy and
cutting ability .
Q.24 What are the different components of EBM ?(Section 2.2.1)
Q.25 State the characteristics of a LASER beam.
Ans. :
1. Directionality 2. Monochromaticity
3. Brightness 4. Coherence
Q.26 What is the principle of LBM ?
Ans. : Laser Beam Machining (LBM) is a form of machining process in which laser beam is
used for the machining of metallic and non-metallic materials. In this process, a laser beam
of high energy is made to strike on the workpiece, the thermal energy of the laser gets
transferred to the surface of the workpiece.
Q.27 Contrast LBM and EBM.
Ans. :
LBM EBM

A high intensity of beam of laser is used to A high intensity beam of focused electrons
supply heat for material removal. is use to supply heat for material removal.

It does not require any vacuum chamber It requires vacuum chamber

There is no restrictions on workpiece size EBM process is suitable for small

components

LBM is independent of electrically Electrically conductive material only can

conductive machined.

Q.28 What are the advantages and disadvantages of LBM ? (Sections 2.3.4 and 2.3.5)
Q.29 List any two gases used in Plasma arc machining.
Ans. : The used gases are argon, helium, hydrogen or a mixture of these

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What is the function of water muffler in PAM ?

Ans. : A device that produces a covering of water around the plasma torch and extends
down to the work surface helps in reducing smoke and noise
Draw the schematic set-up of plasma arc machine. Indicate various parts.
(Fig. 2.22)
What is the main difference between transferred and non-transferred arc mode in the
case of PAM processes ?
Ans.:
Transferred Arc Non-Transferred Arc

The electric arc is constituted between an The electric arc is constituted between an
electrode and the workpiece. electrode and the nozzle.

Work piece is made anode, Nozzle is kept Workpiece is kept electrically neutral.
electrically neutral.

Direct arc plasma torch can be applied to It can be applied to every workpiece
electrically conductive work pieces only. regardless of electrical conductivity.

2.7 Long Answered Questions (Part - B)

Q.1 Explain the process of EDM, its process parameters and applications.
(Section 2.1.9, Fig. 2.9 and Section 2.19)
Q.2 List out the three types of spark generators used in EDM. Describe them.
(Section 2.1.8)
Q.3 With the help of a neat sketch, describe the mechanism of material removal in EDM.
(Section 2.1.10)
Q.4 Explain the different types of control circuits used in EDM process. (Fig. 2.4)
Q.5 Write about various types of flushing system employed in EDM process.
(Section 2.1.15)
Q.6 What are the basic requirements of tool materials in EDM process ? Name any four
tool materials. (Section 2.1.3)
Q.7 Explain the process of wire cut EDM and list its advantages. (Section 2.2.1)
Q.8 Explain the principle of working of wire cut EDM process with a sketch.
(Section 2.2.2)
Q.9 What are the advantages and disadvantages of the wire cut EDM process ?
(Sections 2.2.4 and 2.2.5)

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Q.10 Explain the following on wire EDM technology. (Section 2.2.1)

a. Dielectric system
b. Deionized water
c. Positioning system
d. Wire drive system
Q.11 What is EBM ? Sketch its set-up and indicate its parts and explain the principle of
operation. (Section 2.4.1)
Q.12 Describe the EBM process with a simple sketch and write about its process
parameters, advantages and applications. (Section 2.4)
Q.13 Sketch the electron beam gun and explain the functions of each part. (Fig. 2.21)
Q.14 Explain the principle of LBM with sketch. List out the advantage and limitation of
LBM process. (Section 2.3)
Q.15 List the advantages, disadvantages and applications of LBM process.
(Sections 2.3.4 , 2.3.5 and 2.3.6)
Q.16 Explain the principle of Plasma Arc Machining (PAM). (Section 2.5)
Q.17 List the advantages, disadvantages and applications of PAM.
(Sections 2.5.3, 2.5.4 and 2.5.5)

2.8 Multiple Choice Questions with Answers

ELECTRIC DISCHARGE MACHINING (EDM)

Q.1 In advanced machining processes, what is the full form of EDM ?

a Electro Discharge Machining b Electro Discharge Manufacturing
c Electrical Dimensioning Machining d Electrode Dimensions Manufacturing [Ans. : a]

Q.2 The evolution of wire EDM took place in which part of history ?
a 1940s b 1950s
c 1960s d 1970s [Ans. : d]

Q.3 Machining speeds have gone up to how many times after the invention of EDM ?
a Ten b Twenty
c Thirty d Fifty [Ans. : b]

Q.4 By using EDM, how much percentage of machining costs can be reduced ?
a 10 % b 20 %
c 30 % d 50 % [Ans. : c]

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Q.5 After invention of EDM, surface finish have improved by how much factor ?
a 10 b 15
c 20 d 25 [Ans. : b]

Q.6 Cavities with, which of the following factors can be produced using Electro discharge
machining ?
a Thin walls b Fine features
c Thin walls & Fine features d None of the mentioned [Ans. : c]

Q.7 Which of the following geometries can be machined using EDM ?

a Simple b Complex
c Difficult to cut d All of the mentioned [Ans. : d]

Q.8 State whether the following statement is true or false regarding EDM.
“In EDM, process is affected by hardness of material.”
a True b False [Ans. : b]

Q.9 How much amount of burr is produced in this process ?

a 10 % b 40 %
c 70 % d No burr [Ans. : d]

Q.10 Which of the following mechanisms is used for material removal ?

a Electro discharge erosion b Magnetic abrasion
c Electro chemical dissolution d Mechanical erosion [Ans. : a]

Q.11 What is the value of order of frequency applied between the two electrodes in EDM ?
a 1 kHz b 3 kHz
c 5 kHz d 7 kHz [Ans. : c]

Q.12 What are the magnitude of voltages used in electro discharge machining ?
a 1 to 20 V b 20 to 120 V
c 120 to 220 V d 220 to 320 V [Ans. : b]

Q.13 What are the values of gaps between the electrodes in EDM ?
a 0.001 - 0.05 mm b 0.01 - 0.5 mm
c 0.1 - 5 mm d 1 - 15 mm [Ans. : b]

Q.14 How is material removed in electro discharge machining ?

a Melt and evaporate b Corrode and break
c Mechanical erosion takes place d None of the mentioned [Ans. : a]

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Q.15 What is the radius of channel, when electrical breakdown occur ?

a 4 μm b 6 μm
c 8 μm d 10 μm [Ans. : d]

Q.16 State whether the following statement is true or false regarding EDM.
“In EDM, negative ions (electrons) collide with positive ions to generate heat.”
a True b False [Ans. : b]

Q.17 What are the values of temperature that are obtained while machining using EDM ?
a 2000 to 3000 ºC b 4000 to 6000 ºC
c 8000 to 12000 ºC d 15000 to 20000 ºC [Ans. : c]

Q.18 What range of heat fluxes are obtained while machining using EDM ?
a 1017 W/m2 b 1019 W/m2
c 1024 W/m2 d 1027 W/m2 [Ans. : a]

Q.19 What is the duration of sparks that are produced in Electro discharge machining ?
a 0.001 - 1 μs b 0.1 - 2000 μs
c 0.2 - 100 ms d 100 - 2000 ms [Ans. : b]

Q.20 State whether the following statement is true or false about material removal in EDM.
“In EDM, high pressures allow the metal to evaporate.”
a True b False [Ans. : b]

Q.21 What are the values of pressure of the plasma in EDM ?

a Up to 2 atm b Up to 20 atm
c Up to 200 atm d Up to 2000 atm [Ans. : c]

Q.22 At the end of pulse, super-heated metal evaporates .

a explosively b normally
c periodically d occasionally [Ans. : a]

Q.23 After the explosion is over, how is the debris carried away ?
a Evaporation b Fresh dielectric
c Old dielectric d All of the mentioned [Ans. : b]

Q.24 The layer formed when unexpelled molten metal solidifies is known as .
a reabsorbed layer b recast layer
c unevaporated layer d condensed layer [Ans. : b]

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Q.25 Amount of material removed from anode and cathode depend on which of the
following ?
a Electrons b Positive ions
c Electrons & Positive ions d None of the mentioned [Ans. : c]

Q.26 What happens when the electron current predominates in the discharge ?
a More anodic removal b More cathodic removal
c Remains same d All of the mentioned [Ans. : a]

Q.27 Between what values mentioned below, do the discharges and sparks usually vary ?
a 1 and 10,000 b 500 and 500,000
c 500,000 and 1,000,000 d None of the mentioned [Ans. : b]

Q.28 What is the value of gap maintained between the electrodes when we use servo
mechanism ?
a 10 - 100 μm b 100 - 200 μm
c 200 - 500 μm d 500 - 1000 μm [Ans. : c]

Q.29 Based on the electrode gap, which of the following electric pulses are generated ?
a Open Circuit pulses b Sparks
c Arcs d All of the mentioned [Ans. : d]

Q.30 State whether the following statement is true or false regarding EDM.
“In Electro discharge machining, electric pulses generated affect the material removal.”
a True b False [Ans. : a]

Q.31 Open gap voltages contribute to how much amount of material removal ?
a 20 % b 50 %
c 70 % d No contribution [Ans. : d]

Q.32 When the electrode gap is too small or electrodes are in contact, how much material is
removed ?
a 10 % b 20 %
c 30 % d No material removed [Ans. : d]

Q.33 Which components mentioned below are affected due to arcs ?

a Work piece b Tool
c Work piece & Tool d None of the mentioned [Ans. : c]

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Q.34 Which of the following pulses contribute to the desired material removal in EDM ?
a Open circuit pulses b Short circuits
c Arcs d Sparks [Ans. : d]

Q.35 Which of the following are main components of EDM ?

a Dielectric system b Servomechanism
c Power supply d All of the mentioned [Ans. : d]

Q.36 What is the function of feed-control system in electro discharge machining ?

a Constant gap b Supply power
c Dielectric fluid supply d Work piece holding [Ans. : a]

Q.37 What is the use of power supply system in electro discharge machining ?
a Constant gap b Supply power
c Dielectric fluid supply d Work piece holding [Ans. : b]

Q.38 What is the function of dielectric circulation unit in Electro discharge machining ?
a Constant gap b Supply power
c Dielectric fluid supply d Work piece holding [Ans. : c]

Q.39 Which of the following materials are used as electrodes in EDM ?

a Graphite b Copper
c Brass d All of the mentioned [Ans. : d]

Q.40 Metals with melting point and electrical conductivity are chosen as
tools in EDM.
a low, good b low, bad
c high, good d high, bad [Ans. : c]

Q.41 Copper has electro discharge machining wear and conductivity.

a Good, better b Good, worse
c Bad, better d Bad, worse [Ans. : a]

Q.42 Which of the following tungsten carbides are used as electrodes in EDM ?
a Silver tungsten b Copper tungsten
c All of the mentioned d None of the mentioned [Ans. : c]

Q.43 State whether the following statement is true or false regarding materials used in electro
discharge machining.
“In metals, copper graphite has less electrical conductivity than graphite.”
a True b False [Ans. : b]

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Q.44 Brass metal ensures which type of sparking conditions in electro discharge machining ?
a Stable b Unstable
c Unsteady d Insecure [Ans. : a]

Q.45 In addition to the feed of tool, electro discharge machining tool can have which type of
motion ?
a Oscillatory b Rotary
c Vibrational d All of the mentioned [Ans. : b]

Q.46 Which of the following parameters determines the size of cavities ?

a Size of electrode b Radius of orbit
c All of the mentioned d None of the mentioned [Ans. : c]

Q.47 Electrode orbiting the flushing of dielectric fluid in electro discharge

machining.
a Improves b Decreases
c Reduces d Degrades [Ans. : a]

Q.48 Quality of hole produced by orbiting motion is to that obtained by using

stationary electrode.
a inferior b superior
c lower d all of the mentioned [Ans. : b]

Q.49 In EDM, electrode polarity depends up on which of the following components ?

a Work piece b Electrode material
c All of the mentioned d None of the mentioned [Ans. : c]

Q.50 Which one among the following, is the most important factor in determining the tool
wear ?
a Melting point b Boiling point
c Power supplied d Feed rate [Ans. : a]

Q.51 Electrode wear ratios can be expressed as, which of the following wears ?
a End wear b Side wear
c Corner wear d All of the mentioned [Ans. : d]

Q.52 The term no wear in EDM occurs when electro-to-work piece wear ratio is
a <1 % b <3 %
c <5 % d <10 % [Ans. : a]

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Q.53 Which of the following are the other factors that influence the electrode wear ?
a Voltage b Current
c Electrode material d All of the mentioned [Ans. : d]

Q.54 State whether the following statement is true or false regarding wear in EDM.
“In EDM, electrode wear is less dominant when it comes to micromachining applications.”
a True b False [Ans. : b]

Q.55 State whether the following statement is true or false regarding wear in EDM.
“In EDM, corner wear ratio does not depend on type of electrode material.”
a True b False [Ans. : b]

Q.56 In electro discharge machining, highest wear ratio is associated with which type of
melting point ?
a Low b Medium
c High d Very high [Ans. : a]

Q.57 Which of the following is not a function of dielectric in EDM ?

a Flush particles b Cool the section
c Maintain voltage d Provide insulation [Ans. : c]

Q.58 Which of the following are the main requirements of dielectric fluids ?
a Viscosity b High flash point
c Minimum odour d All of the mentioned [Ans. : d]

Q.59 Which of the following can be used as dielectric fluids in EDM ?

a Kerosene b Silicon fluids
c Distilled water d All of the mentioned [Ans. : d]

Q.60 In EDM, inadequate flushing will not result in which of the following consequences ?
a Arcing b Debris removal
c Decrease electrode life d Increased production time [Ans. : b]

Q.61 Which methods below, are used for introducing the dielectric in machining gap ?
a Normal flow b Reverse flow
c Jet flushing d All of the mentioned [Ans. : d]

Q.62 Few large holes are than many small flushing holes in electro discharge
machining.
a worse b better
c well d none of the mentioned [Ans. : a]

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Q.63 State whether the following statement is true or false regarding the dielectric in EDM.
“In EDM, flushing through the tool is more preferred than side flushing.”
a True b False [Ans : a]

Q.64 In Electro discharge machining, which type of dielectric flow mentioned below is
desirable ?
a Unsteady flow b Steady flow
c Unstable flow d None of the mentioned [Ans. : b]

Q.65 Metal is removed on which of the components in electro discharge machining ?

a Electrode tool b Work piece
c Electrode tool & Work piece d None of the mentioned [Ans. : c]

Q.66 On which of the following components, does the MRR depend ?

a Work piece b Electrode tool
c Electrode tool & Work piece d None of the mentioned [Ans. : c]

Q.67 Which of the following factors influence the material removal rate ?
a Pulse condition b Electrode polarity
c Machining medium d All of the mentioned [Ans. : d]

Q.68 In electro discharge machining, materials with low melting point have which type of
material removal rate ?
a Very low b Low
c Medium d High [Ans. : d]

Q.69 In electro discharge machining, materials with low melting point have which type of
surface roughness ?
a Rough b Smooth
c Fine d All of the mentioned [Ans. : a]

Q.70 What are the values of material removal rates in EDM ?

a 0.001 to 0.1 mm3/min b 0.1 to 400 mm3/min
c 400 to 1000 mm3/min d 1000 to 5000 mm3/min [Ans. : b]

Q.71 What happens to the material removal rate if the sparks are very less in EDM ?
a Decreases b Increases
c Increase and then decrease d All of the mentioned [Ans. : a]

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Q.72 What is the relation between the melting point and the material removal rate ?
a Directly proportional b Inversely proportional
c Indirectly proportional d None of the mentioned [Ans. : b]

Q.73 What happens to the crater size if we increase the current keeping the pulse time
constant ?
a Increase b Decrease
c Decrease and increase d None of the mentioned [Ans. : a]

Q.74 What happens to the crater size if we decrease the pulse time keeping the current
constant ?
a Increase b Decrease
c Increase and decrease d None of the mentioned [Ans. : b]

Q.75 On which of the following factors do the craters depend ?

a Physical properties b Mechanical properties
c Composition of medium d All of the mentioned [Ans. : d]

Q.76 The maximum depth of damaged layer is how many times that of average surface
roughness ?
a 1.5 times b 2 times
c 2.5 times d 3 times [Ans. : c]

Q.77 What happens to the surface roughness values if the MRR increases in EDM ?
a Increases b Decreases
c Decrease and increase d None of the mentioned [Ans. : a]

Q.78 State whether the following statement is true or false regarding the surface roughness in
EDM.
“In EDM, graphite electrodes produce smoother surfaces than metal ones.”
a True b False [Ans. : b]

Q.79 In electro discharge machining, what happens to the surface finish if the pulse energy is
decreased ?
a Reduces b Decreases
c Improves d None of the mentioned [Ans. : c]

Q.80 Using of a mate electrode in electro discharge machining the surface

roughness of material.
a Increases b Decreases
c Enhances d None of the mentioned [Ans. : b]

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Q.81 What happens to the surface roughness if oxygen gas is introduced in the gap ?
a increases b decreases
c decrease and then increase d all of the mentioned [Ans. : b]

Q.82 By how much percent surface roughness is reduced if we use proper dielectric flow ?
a 25 % b 50 %
c 75 % d 100 % [Ans. : b]

Q.83 What are the tolerance values obtained by machining using EDM ?
a ± 10 mm b ± 15 mm
c ± 25 mm d ± 40 mm [Ans. : c]

Q.84 How much extra tolerances are achieved when we choose proper variables ?
a ± 5 mm b ± 10 mm
c ± 15 mm d ± 20 mm [Ans. : a]

Q.85 What are the values of temperatures obtained in electro discharge machining ?
a 1000 to 2000 ºC b 2000 to 4000 ºC
c 4000 to 8000 ºC d 8000 to 12000 ºC [Ans. : d]

Q.86 What is the value of thickness of recast layer obtained when power of 5 μJ is given ?
a 1 μm b 3 μm
c 5 μm d 7 μm [Ans. : a]

Q.87 What are the values of thickness of recast layers in electro discharge machining ?
a 0.001 to 0.025 μm b 0.01 to 0.25 μm
c 1 to 25 μm d 10 to 250 μm [Ans. : c]

Q.88 In electro discharge machining, some annealing of the work piece can be expected
the machined surface.
a on b just below
c above d at bottom [Ans. : b]

Q.89 The depth of the annealed surface is to the amount of power used in
machining operation.
a directly proportional b inversely proportional
c exponential d all of the mentioned [Ans. : a]

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Q.90 What are the values of thickness of annealed surface obtained while machining using
EDM ?
a 1 to 25 μm b 50 to 200 μm
c 200 to 500 μm d 500 to 1000 μm [Ans. : b]

Q.91 In EDM, choosing electrodes that produce which type of machining reduces the
annealing effect?
a Stable b Unstable
c Uneven d All of the mentioned [Ans. : a]

Q.92 What happens to the fatigue strength of alloys if altered surfaces are produced in electro
discharge machining ?
a Increases b Reduces
c Enhances d Improves [Ans. : b]

Q.93 The altered layers formed during the process of EDM consists of which of the
following ?
a Tempered layers b Heat affected zones
c Intergranular precipitates d All of the mentioned [Ans. : d]

Q.94 During roughing process through electro discharge machining, what is the thickness of
layer formed ?
a < 0.075 mm b < 0.125 mm
c < 0.500 mm d < 0.750 mm [Ans. : b]

Q.95 During finishing process through electro discharge machining, what is the value
thickness of layer formed ?
a <0.075 mm b <0.125 mm
c <0.500 mm d <0.750 mm [Ans. : a]

Q.96 Which of the following processes can be used for restoration of fatigue properties ?
a Low-stress grinding b Chemical machining
c Reheat treatment d All of the mentioned [Ans. : d]

Q.97 State whether the following statement is true or false regarding the HAZ in EDM.
“In EDM, post treatment to recover fatigue strength is not recommended.”
a True b False [Ans. : b]

Q.98 Which of the following shapes can be produced using electro discharge machining ?
a Complex shapes b Simple shapes
c All of the mentioned d None of the mentioned [Ans. : c]

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Q.99 Which of the following materials can be machined using electro discharge machining ?
a Heat resistant alloys b Super alloys
c Carbides d All of the mentioned [Ans. : d]

Q.100 Which of the following are the applications of electro discharge machining ?
a Holes b Slots
c Texturing d All of the mentioned [Ans. : d]

Q.101 State whether the following statement is true or false regarding the applications of EDM.
“In advanced machining processes, the incorporation of EDM with CIM increased the length of
time for unit operation.”
a True b False [Ans. : b]

Q.102 Which type of electrode is used for drilling in electro discharge machining ?
a Flat electrode b Cuboidal electrode
c Tubular electrode d Spherical electrode [Ans. : c]

Q.103 The dielectric fluid is flushed in thorough which part of the electrode in drilling in EDM?
a Interior hole b Side gaps
c All of the mentioned d None of the mentioned [Ans. : a]

Q.104 Which type of holes can be produced through drilling using electro discharge
machining ?
a Irregular b Curved
c Tapered d All of the mentioned [Ans. : d]

Q.105 What are the values of general feed rates used for drilling in EDM ?
a 0.1 mm/min b 0.3 m/min
c 0.5 mm/min d 0.7 mm/min [Ans. : a]

Q.106 What are range of diameter values obtained by drilling using EDM ?
a 0.01 to 0.05 mm b 0.1 to 0.5 mm
c 1 to 5 mm d 10 to 15 mm [Ans. : b]

Q.107 What are the values of overcuts left behind after drilling of work piece ?
a 0.01 to 0.05 mm b 0.1 to 0.5 mm
c 1 to 5 mm d 10 to 15 mm [Ans. : a]

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Q.108 Electro discharge sawing is an application of EDM which employs as tool

material.
a steel band b disc
c steel band & Disc d none of the mentioned [Ans. : c]

Q.109 When compared to the conventional abrasive sawing, how many times faster is the
MRR ?
a Twice b Thrice
c Four d Five [Ans. : a]

Q.110 How much amount of burr is produce while machined using electro discharge sawing ?
a 10 % b 20 %
c 50 % d No Burr [Ans. : d]

Q.111 What are the values of finish obtained by machining work piece thorough electro
discharge sawing ?
a 0.1 to 4 μm b 6.3 to 10 μm
c 12.4 to 23 μm d 25.6 to 40 μm [Ans. : b]

Q.112 What are the recast layer thickness values obtained in ED sawing ?
a 0.001 to 0.022 mm b 0.025 to 0.130 mm
c 0.236 to 0.352 mm d 0.432 to 0.568 mm [Ans. : b]

Q.113 Which of the following electrodes are used for machining spherical surfaces in electro
discharge machining ?
a Tubular electrodes b Flat electrodes
c Cuboidal electrodes d All of the mentioned [Ans. : a]

Q.114 What are the values of dimensional accuracy obtained while machining spherical
surfaces ?
a ± 1 μm b ± 3 μm
c ± 5 μm d ± 7 μm [Ans. : a]

Q.115 What are the surface roughness values obtained while machining spherical surfaces
using electro discharge machining ?
a < 0.1 μm b < 0.3 μm
c < 0.5 μm d < 0.7 μm [Ans. : a]

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Q.116 Which motion of tool is used for machining spherical surfaces in electro discharge
machining ?
a Oscillatory b Vibratory
c Rotary d All of the mentioned [Ans. : c]

Q.117 Which type of electrodes are used for milling application in electro discharge machining
process ?
a Tubular type electrodes b Cylindrical type electrodes
c Flat type electrodes d Spherical type electrodes [Ans. : b]

Q.118 Which type of cavities can be machined using milling process by electro discharge
machining ?
a Complex cavities b Simple cavities
c Simple & Complex cavities d None of the mentioned [Ans. : c]

Q.119 The simple electrodes are rotated at which speed for milling of work pieces in electro
discharge machining ?
a Very low b Low
c Medium d High [Ans. : d]

Q.120 What happens to the dielectric flushing while milling tool is rotated at a high speed in
EDM ?
a Improved b Worsen
c Reduced d All of the mentioned [Ans. : a]

Q.121 State whether the following statement is true or false regarding the applications of EDM.
“In EDM, milling process can machine complex shapes with sharp corners.”
a True b False [Ans. : b]

Q.122 Which of the following are the steps included in the die sinking process of EDM ?
a CAD of electrode b Electrode manufacturing
c Programming for die sinking d All of the mentioned [Ans. : d]

Q.123 Wire EDM is a special form of electro discharge machining which contains
electrode.
a continuously moving b periodically moving
c discontinuously moving d all of the mentioned [Ans. : a]

Q.124 Which path of the components in wire EDM determines the path to be machined ?
a Horizontal worktable movement b Vertical worktable movement
c Horizontal & Vertical worktable movement d None of the mentioned [Ans. : a]

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Q.125 Which of the following materials are machined using wire electro discharge
machining ?
a Polycrystalline diamond b Cubic Boronitride
c Matrix composites d All of the mentioned [Ans. : d]

Q.126 How much amount of burr is produce when we use wire electro discharge machining for
machining of work pieces ?
a 10 % b 20 %
c No burr d Small amount [Ans. : c]

Q.127 Which of the following industries use wire EDM for different applications ?
a Chemical industry b Aerospace industry
c Automobile industry d All of the mentioned [Ans. : d]

Q.128 While machining insulating ceramic materials using EDM, where is the sheet metal
placed ?
a Over material b Below material
c Under material d None of the mentioned [Ans. : a]

Q.129 Sparks occur between which of the following components ?

a Work piece and sheet metal b Tool electrode and sheet metal
c Work piece and electrode d None of the mentioned [Ans. : b]

Q.130 Texturing is applied to the steel sheets at which stages of cold rolling ?
a Initial stages b Middle stages
c Final stages d All of the mentioned [Ans. : a]

Q.131 What is the full form of EDT in EDM processes ?

a Electro Discharge Tinplating b Electro Discharge Texturing
c Electro Discharge Tapping d Electro Discharge Turing [Ans. : b]

Q.132 Which of the following are the process variables for texturing process in EDM ?
a Pulse current b Electrode polarity
c Dielectric type d All of the mentioned [Ans. : d]

Q.133 What are the values of current amplitudes used in EDT ?

a 0.2 to 1 A b 2 to 10 A
c 20 to 100 A d 40 to 200 A [Ans. : b]

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Q.134 What are duration values of current amplitude in EDT ?

a 0.1 to 1 μs b 1 to 10 μs
c 10 to 100 μs d 100 to 1000 μs [Ans. : c]

Q.135 What are the spindle rotation speeds used in EDT ?

a 1 to 4 rpm b 10 to 40 rpm
c 20 to 60 rpm d 30 to 90 rpm [Ans. : b]

Q.136 What are the values of diameter which are machined using Micro-EDM ?
a 0.001 to 0.01 mm b 0.01 to 0.1 mm
c 0.1 to 1 mm d 1 to 10 mm [Ans. : c]

Q.137 What happens to the machine capital cost in EDT when there is an increase in tool
quantity ?
a Decreases b Increases
c Remains same d None of the mentioned [Ans. : b]

Q.138 What is the value of depth to diameter ratio in Micro-Electro discharge machining
process ?
a 10 : 1 b 5:2
c 4:3 d 2:1 [Ans. : a]

Q.139 What are the values of depths that can be machined using Micro-EDM ?
a 1 mm b 10 mm
c 100 mm d 1000 mm [Ans. : c]

Q.140 What are the machining rates used in Micro-EDM process ?

a 0.1 to 2 mm/min b 1 to 20 mm/min
c 10 to 200 mm/min d 100 to 500 mm/min [Ans. : b]

Q.141 What are the values of hole diameters obtained using wire electro discharge grinding ?
a 1 μm b 3 μm
c 5 μm d 7 μm [Ans. : c]

Q.142 What are the feed rates used in WEDG process ?

a 1 to 5 mm/min b 5 to 10 mm/min
c 10 to 15 mm/min d 15 to 20 mm/min [Ans. : b]

Q.143 Which of the following is a major difficulty in the electro discharge machining process ?
a Proper sparks b Abnormal discharges
c Optimum feed rates d No burr [Ans. : b]

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Q.144 What has been done to the off time when there is a no-load voltage of electric
discharge ?
a Increased b Decreased
c Reduced d Remains same [Ans. : a]

Q.145 In a simple application which of the following parameters are inputs ?

a Pulse duration and current b Normal and abnormal pulses
c All of the mentioned d None of the mentioned [Ans. : a]

Q.146 In a simple application which of the following parameters are outputs ?

a Pulse duration and current b Normal and abnormal pulses
c All of the mentioned d None of the mentioned [Ans. : a]

Q.147 Which of the following are correlated with the machining conditions at output stage ?
a Machining depth b Surface roughness
c Accuracy d All of the mentioned [Ans. : d]

Q.148 How are EDM’s levels of integration when compared to conventional machining ?
a Slower rate b Faster rate
c Same rate d None of the mentioned [Ans. : a]

Q.149 Manufacturing of tool electrode undergoes which of the following processes ?

a Milling b Turning
c Finishing d All of the mentioned [Ans. : d]

Q.150 High temperatures produced in the working gap results in which of the following
potentials ?
a Hazardous smoke b Toxic vapours
c Aerosols d All of the mentioned [Ans. : d]

Q.151 Hydro carbons present in the dielectric fluid have impact on which of the body parts ?
a Eyes b Teeth
c Skin d Nails [Ans. : c]

Q.152 What happens to the electro discharge machining process under unfavourable working
conditions ?
a Will remain stable b Explosion may occur
c Machining rate increases d Nothing happens [Ans. : b]

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Q.153 Reduction in the electrical energy consumption will have impact on which aspects
mentioned below ?
a Environmental b Economic
c Environmental & Economic d None of the mentioned [Ans. : c]

WIRECUT EDM

Q.154 Wire Electric Discharge (ED) machining is based on the same principle as that of .
a hydro-dynamic EDM b die-sink EDM
c polar EDM d non-conventional EDM [Ans. : b]

Q.155 The only difference between die-sink EDM and wire cut EDM is the .
a way of material removal b electrode used for the machining
c type of materials machined d processing time [Ans. : b]

Q.156 During wire cut EDM, the size of the cavity produced by the wire while machining
depends upon .
a material of the workpiece b di-electric fluid used
c wire material d electric current [Ans. : d]

Q.157 Sparking gap is the distance between .

a the workpiece and the CNC table b the workpiece and the electrode wire
c the electrode wire and the di-electric fluid d the workpiece and the spark plug [Ans. : b]

Q.158 The absolute minimum inner corner radius is .

a the wire radius minus the sparking gap width
b the sparking gap width minus the wire radius
c the wire radius plus the sparking gap width
d double of the wire radius [Ans. : c]

Q.159 The wire ED machines have programmable axes.

a 2 b 2-5
c 6 d 3-9 [Ans. : b]

Q.160 Which of the following component of the wire cut EDM machine does not get heated ?
a Workpiece b Electrode wire
c Di-electric fluid d Coils [Ans. : b]

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Q.161 Which of the following material properties sets restrictions to use wire cut EDM ?
a Material type b Melting point
c Material hardness d Electrical conductivity [Ans. : d]

Q.162 Wires used in wire cut EDM are usually disposed after one usage.
a True b False [Ans. : a]

Q.163 The electrode wires are usually made form .

a graphite b iron
c nickel d brass [Ans. : d]

Q.164 In wire-cut EDM process, material removal takes place by a series of discrete
discharges between
a di-electric fluid and the wire electrode b the wire-electrode and the workpiece
c the workpiece and the CNC-table d wire electrodes [Ans. : b]

Q.165 The di-electric fluid gets ionizes in between gap.

a tool-electrode b cathode-anode
c workpiece-electrode d tool-workpiece [Ans. : a]

Q.166 The burr or cut particles are flushed away by the .

a electrode b motion of the workpiece
c di-electric fluid d coolant [Ans. : c]

Q.167 Wire-cut EDM (WEDM) process is widely used for .

a alloy steels b tool steels
c stainless steels d carbon steels [Ans. : b]

Q.168 For which of the following materials wire-cut EDM is not used ?
a Aluminium b Zirconium
c Steels d Titanium [Ans. : b]

Q.169 WEDM process can be used for cutting hard extrusion dies.
a True b False [Ans. : a]

Q.170 WEDM process can be used for manufacturing of micro-tools.

a True b False [Ans. : a]

Q.171 How many subsystems are there in wire-cut EDM process ?

a 2 b 3
c 4 d 5 [Ans. : c]

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Q.172 Di-electric system used in WEDM process is similar to that of the process.
a conventional drilling b conventional milling
c conventional EDM d broaching [Ans. : c]

Q.173 In wire-cut EDM, a moving wire is used to .

a remove the burr b cut complex outlines
c melt the material d make the way for the di-electric fluid [Ans. : b]

Q.174 Wire Electric Discharge (ED) machining is based on the same principle as that of .
a hydro-dynamic EDM b die-sink EDM
c polar EDM d non-conventional EDM [Ans. : b]

Q.175 The only difference between die-sink EDM and wire cut EDM is the .
a way of material removal b electrode used for the machining
c type of materials machined d processing time [Ans. : b]

Q.176 During wire cut EDM, the size of the cavity produced by the wire while machining
depends upon .
a material of the workpiece b di-electric fluid used
c wire material d electric current [Ans. : d]

Q.177 Sparking gap is the distance between

a the workpiece and the CNC table b the workpiece and the electrode wire
c the electrode wire and the di-electric fluid d the workpiece and the spark plug [Ans. : b]

Q.178 The absolute minimum inner corner radius is

a the wire radius minus the sparking gap width
b the sparking gap width minus the wire radius
c the wire radius plus the sparking gap width
d double of the wire radius [Ans. : c]

Q.179 The wire ED machines have programmable axes.

a 2 b 2-5
c 6 d 3-9 [Ans. : b]

Q.180 Which of the following component of the wire cut EDM machine does not get heated ?
a Workpiece b Electrode wire
c Di-electric fluid d Coils [Ans. : b]

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Q.181 Which of the following material properties sets restrictions to use wire cut EDM ?
a Material type b Melting point
c Material hardness d Electrical conductivity [Ans. : d]

Q.182 Wires used in wire cut EDM are usually disposed after one usage.
a True b False [Ans. : a]

Q.183 The electrode wires are usually made form

a graphite b iron
c nickel d brass [Ans. : d]

Q.184 grades wire are used in automatic re-threading mechanisms.

a Malleable b Softer
c Harder d Commercial [Ans. : c]

Q.185 For machining of high melting point materials, wires are used.
a gallium b zinc coated
c aluminium coated d silver [Ans. : b]

Q.186 is/are used as di-electric fluid in die sink EDM process.

a Pure water b Silicone gel
c Petroleum products d Epoxy resins [Ans. : c]

Q.187 Which of the following is not the application of wire cut EDM process ?
a Machining ejector holes b Cutting the ejector pins
c Machining cores of various moulds d Machining of complex shapes made of plastic

[Ans. : d]

Q.188 During mould making by wire cut EDM, it is important to harden to counter the
effects of changes in the shape of the workpiece due to heat treatment.
a the insert b electrode wire
c electrode holding coils d bolting points in the workpiece [Ans. : a]

Q.189 Which of the following machining process is usually preferred for cutting of ejectors
which are used in mould making ?
a Milling b Hobbing
c Wire-cut EDM d Die sink EDM [Ans. : c]

Q.190 How many ways are there for making the fixed cores by wire cut EDM process ?
a 2 b 3
c 4 d 5 [Ans. : a]

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Q.191 The selection of the manufacturing process depends upon .

a chemical reactivity between the mould material and the di-electric fluid
b mould shape c application of the mould
d number of parts to be machined [Ans. : b]

Q.192 The wire EDM process is used for making moulds with high drafted walls.
a True b False [Ans. : a]

Q.193 For manufacturing of complex shapes, soft electrode wires are used.
a True b False [Ans. : a]

Q.194 Which of the following materials is not machined by wire cut EDM ?
a Inconel b Graphite
c Tool steel d Hastaloy [Ans. : d]

Q.195 Which of the following does not hold true about wire cut EDM ?
a The electrode wire touches the workpiece while cutting the workpiece material
b It can machine any electrically conductive material irrespective of its hardness
c The di-electric fluid gets ionized in between the tool-electrode gap
d During machining, the electrode wire does not get heated [Ans. : a]

Q.196 Which of the following is true about wire cut EDM ?

a Minimal clamping forces are required to hold the workpieces
b It is a conventional process
c It can machine materials like fibres, plastics, wood, etc
d Electrodes used in die sink EDM and wire cut EDM are same [Ans. : a]

Q.197 Which of the following is true about wire cut EDM ?

a It leaves no residual burrs
b It cannot machine materials having hardness beyond 20 BHN
c It has poor accuracy as compared to milling
d It uses petroleum products as di-electric fluid [Ans. : a]

Q.198 Large scale wire cut EDM machines can handle workpieces weighing upto
pounds.
a 100 b 600
c 1000 d 10000 [Ans. : d]

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Q.199 Wire cut EDM process can cut tapers of degrees.

a 5 - 10 b 8 - 16
c 20 - 30 d 25 - 45 [Ans. : c]

Q.200 Wire cut EDM machines work on current.

a direct b alternating
c both direct and alternating d eddy [Ans. : c]

Q.201 The heat of each electrical spark generated during machining is around
Fahrenheit
a 1,000° to 2,000° b 1,100° to 5,000°
c 10,000° to 12,000° d 15,000° to 21,000° [Ans. : d]

Q.202 The de-ionised water is used for flush away the burr as well as to cool the workpiece.
a True b False [Ans. : a]

Q.203 In wire cut EDM, machine movement is accomplished with precision lead screws with
recirculating ball bearings.
a True b False [Ans. : a]

Q.204 Copper is not used for making electrode wires in wire cut EDM because of its .
a good conductivity b lower tensile strength
c high melting point d higher purchasing cost [Ans. : b]

Q.205 Which of the following materials is not used for electrode wires ?
a Molybdenum b Brass
c Steel d Graphite [Ans. : c]

Q.206 Selection of the wire is based on how many factors ?

a 2 b 3
c 4 d 5 [Ans. : c]

Q.207 The diameter of the electrode wire is in the range of .

a 0.001″ - 0.0035″ b 0.003″ - 0.004″
c 0.004″ - 0.014″ d 0.020″ - 0.032″ [Ans. : c]

Q.208 After originating from a supply spool, the wire is passed through .
a a chamber filled with special stones b diamond guides
c a furnace d a container filled with anti-oxidant [Ans. : b]

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Q.209 With the addition of the programmable to wire cut EDM machine, workpieces of
different thicknesses can be machined.
a X-axis b Y-axis
c Z-axis d chuck [Ans. : c]

Q.210 In a wire break situation, the end of the wire is while the supply wire is
a clamped, drawn back b drawn back, clamped
c dipped in the di-electric fluid, clamped d welded with the other wire, drawn back [Ans. : a]
Q.211 The automatic wire threading offers the ability to cut multiple openings in a workpiece
without operator intervention.
a True b False [Ans. : a]

Q.212 If there is a wire break during machining, the machine returns to the start point.
a True b False [Ans. : a]

Q.213 After a wire break, the wire tip segment that was clamped is disposed off in a wire tip
disposal unit.
a True b False [Ans. : a]

Q.214 In wire cut EDM machine, axes are positioned away from the work area to avoid
moisture and contamination.
a X and Y b X and Z
c U and V d Y and V [Ans. : c]

Q.215 The U and V axes provide movement to the wire to produce taper angles upto
degrees.
a 15 b +/– 20
c +/– 30 d 45 [Ans. : c]

Q.216 During the wire cut EDM process, the feature of adjustable tapering values is useful for
.
a circular workpieces b mould applications
c thick workpieces d forging dies [Ans. : b]

Q.217 The function of independent programming of the U & V axes in wire cut EDM machines
is for .
a hexagonal workpieces b fullerene shaped workpieces
c workpieces having a different shape on the top and bottom
d workpieces having intricate shapes [Ans. : c]

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Q.218 Which of the following is not machined by wire cut EDM ?

a Airfoils b Extrusion dies
c Square shaped objects d Perforated sheets [Ans. : d]

Q.219 How many sections does the di-electric system includes ?

a 2 b 3
c 4 d 5 [Ans. : c]

Q.220 While machining, the dirty water is filtered through a .

a paper filter b notch filters
c comb filters d fir filters [Ans. : a]

Q.221 In a wire cut EDM machine, is used to control the resistivity of the de-electric fluid
(water).
a resin beds b water reservoir
c de-ionisation system d diamond guides [Ans. : a]

Q.222 A water chiller is used to keep thermally stable.

a electrode wire b electrode coils
c control arms d dielectric reservoir [Ans. : c]

Q.223 During the cutting process water conductivity level changes due to eroded chips.
a True b False [Ans. : a]

Q.224 Submerged machining is extremely useful for applications that generally have
a poor flushing conditions b intricate shapes
c tapered sections d good weldability [Ans. : a]

Q.225 Submerged machining is used for .

a cutting small taper angles b tiny workpieces
c laminations d workpieces with no undercuts [Ans. : c]

Q.226 There is a greater risk of breaking a wire if .

a temperature of the wire is too high b larger taper angles are to be cut
c the flush is not set properly d there is an inadequate flow of di-electric fluid

[Ans. : c]

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Q.227 How many of the following processes does not need submerged machining
capabilities?

- starting a cut from the edge of a workpiece

- slicing a tube
- slicing a bar stock

- starting a cut from a large diameter start hole.

a 1 b 2
c 3 d 4 [Ans. : d]

Q.228 When parts with existing openings in them must be cut, conventional flushing produces

a air pockets b unnecessary tapers

c undercuts d poor flushing [Ans. : a]

Q.229 When it is not possible to have the flushing nozzles close to the top or bottom of the
workpiece machines may require constant adjustment of the top and bottom flush.
a submerged type b splash flush
c rigid flush d stock flush [Ans. : b]

Q.230 Which of the following is not the benefit of submerged cutting ?

a improved accuracy b better surface finish
c Thermal stability d no wire breakage [Ans. : d]

Q.231 Submerged cutting helps cutting the workpieces without hampering the flush.
a True b False [Ans. : a]

Q.232Which of the following is not the effect of less maintenance of the wire cut EDM
machines?
a Wire breaks b Lines in the part
c Lowered time to complete the job d Rough surfaces [Ans. : c]

Q.233 In how many of the following applications, wire cut EDM can be used ?
- Manufacturing of progressive, blanking and trim dies
- Extrusion dies
- Cutting difficult to machine materials like hastaloy, inconel and titanium
- Cutting narrow slots and keyways
- Manufacturing of parts where burrs can’t be tolerated.
a 1 b 3
c 4 d 5 [Ans. : d]

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LASER BEAM MACHINING

Q.234 Mechanism of material removal in laser beam machining is due to .
a mechanical erosion due to impact of high of energy photons
b electro-chemical etching
c melting and vaporisation due to thermal effect of impingement of high energy laser beam
d fatigue failure [Ans. : c]

Q.235 Laser beam is produced due to

a spontaneous emission
b stimulated emission followed by spontaneous emission
c spontaneous emission followed by Spontaneous absorption
d spontaneous absorption leading to “population inversion” and followed by stimulated emission

[Ans. : d]

Q.236 Which of the following processes does not use lasers ?

a Cladding b Alloying
c Nitriding d Cutting [Ans. : c]

Q.237 Lasers are also used for

a riveting b nitriding
c rapid prototyping d facing [Ans. : c]

Q.238 Laser stands for light amplification by stimulated emission of radiation.

a True b False [Ans. : a]

Q.239 Laser beams can have power density upto

a 1 kW/mm2 b 10 kW/mm2
c 1 MW/mm2 d 10 MW/mm2 [Ans. : c]

Q.240 Laser causes a rapid substantial rise in of the material.

a local temperature b local pressure
c indentation d cracks [Ans. : a]

Q.241 At temperature an atom is considered to be at ground level.

a absolute zero b 0 oC
c 100 oC d 100 K [Ans. : a]

Q.242 The electrons at ground state can be excited to a higher state of energy by
a increasing the pressure b lowering the energy
c absorbing the energy d oxidising the atom [Ans. : c]

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 Thermal and Electrical Energy Based Processes

Q.243 The geometry and radii of orbital paths of electrons depend on the presence of an
electromagnetic field.
a True b False [Ans. : a]

Q.244 When coming back to normal state from excited state, electron releases
a proton b anti-proton
c positron d photon [Ans. : d]

Q.245 In population inversion, no of electrons in are more as compared to numbers of

electrons in .
a quasi-stable state, ground state b meta-stable state, ground state
c meta-stable state, quasi-stable state d mono-stable state, ground state [Ans. : b]

Q.246 In laser beam machine, one end of the glass is .

a open b blocked with a 10 % reflective mirror
c blocked with a 75 % reflective mirror d blocked with a 100 % reflective mirror [Ans. : d]

Q.247 In laser beam machining, electrons are excited by .

a high temperature steam b flash lamps
c flash torch d cathode ray tube [Ans. : b]

Q.248 The photons emitted in the direction form a laser beam.

a vertical b horizontal
c longitudinal d lateral [Ans. : c]

Q.249 How many types of lasers are there ?

a 2 b 3
c 4 d 5 [Ans. : a]

Q.250 How many types of solid state lasers are there ?

a 2 b 3
c 4 d 5 [Ans. : b]

Q.251 Lasers can be operated in modes.

a 2 b 7
c 8 d only one [Ans. : a]

Q.252 Helium-Neon is a gas laser.

a True b False [Ans. : a]

Q.253 Flash tubes used for Nd-YAG laser can be helical or flat.
a True b False [Ans. : a]

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 Thermal and Electrical Energy Based Processes

Q.254 The flash tube is operated in mode.

a pulsed b continuous
c reversed d synchronous [Ans. : a]

Q.255 How many types of flows are possible in gas lasers ?

a 2 b 3
c 4 d 5 [Ans. : b]

Q.256 The power of CO2 laser is around

a 15 watt per meter of tube length b 55 watt per meter of tube length
c 100 watt per meter of tube length d 1 MW per meter of tube length [Ans. : c]

Q.257 In a CO2 laser, a mixture of is circulated through the gas tube.

a CO2, N2 and He b CO2, N2 and Ar
c CO2, H2 and N2 d CO2, I2 and O2 [Ans. : a]

Q.258 In CO2 laser, ‘He’ gas is used for cooling purpose.

a True b False [Ans. : a]

Q.259 CO2 lasers are folded to achieve

a high power b high depth of cuts
c high material removal rate d avoid over heating [Ans. : a]

Q.260 Nd-YAG laser can be used for drilling holes in the range of diameter.
a 0.25 mm - 1.5 mm b 1 mm - 1.5 mm
c 1.5 mm - 2 mm d 2 mm - 2.5 mm [Ans. : a]

Q.261 For which of the following materials CO2 laser is not used?
a Plastics b Metals
c Organic materials d Ceramics [Ans. : b]

Q.262 Which of the following does not hold true about laser beam machining?
a High initial cost b High running cost
c No heat affected zone d It is not suitable for heat sensitive materials
[Ans. : c]

Q.263 Using lasers, large aspect ratio in drilling can be achieved.

a True b False [Ans. : a]

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 Thermal and Electrical Energy Based Processes

ELECTRON BEAM MACHINING

Q.264 Mechanism of material removal in Electron Beam Machining is due to
a mechanical erosion due to impact of high of energy electrons
b chemical etching by the high energy electron
c sputtering due to high energy electrons
d melting and vaporisation due to the thermal effect of impingement of high energy electron
[Ans. : d]

Q.265 Electron beam machining is a/an process

a adiabatic b thermal
c iso-thermal d isentropic [Ans. : b]

Q.266 Electron beam machining is carried out in

a high pressure vessel b thermally insulated area
c vacuum d in a room at atmospheric pressure [Ans. : c]

Q.267 During EBM is kept under vacuum.

a electron gun b whole setup
c the workpiece d laser generation setup [Ans. : c]

Q.268 As the electrons strike the work material

a heat energy is converted to kinetic energy b atomic energy is converted to heat energy
c kinetic energy is converted to heat energy d electrical energy is converted to heat energy
[Ans. : c]

Q.269 The gun in EBM is used in mode.

a wave guide b biasing
c pulsed d high intensity [Ans. : c]

Q.270 Which of the following is not a function of electron beam gun ?

a generation of electrons b accelerating the electrons
c focusing the beam d absorbing the electron beam [Ans. : d]

Q.271 is used to make cathode for electron beam gun.

a Aluminium b Rubidium
c Molybdenum d Tantalum [Ans. : d]

Q.272 Heating to a high temperature leads to thermo-ionic emission.

a True b False [Ans. : a]

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Q.273 In the electron beam gun, cathode cartridge is highly negatively biased.
a True b False [Ans. : a]

Q.274 In electron beam machine, just after the cathode, there is/are .
a deflector coils b a magnetic lens
c bias grid d port for vacuum gauge [Ans. : c]

Q.275 Electron is accelerated by .

a cathode cartridge b electromagnetic coils
c aperture d annular anode [Ans. : d]

Q.276 determines the mode of an electron beam.

a Applied voltage b Operating pressure
c Position of magnetic lens d The nature of biasing [Ans.: d]

Q.277 After the anode, the electron beam passes through .

a cathode cartridge b deflector coils
c bias grid d a series of lenses [Ans. : d]

Q.278 In the electron beam gun, apertures .

a allow only convergent electrons to pass b absorb convergent electrons
c allow divergent electrons to pass d accelerate the electron beam [Ans. : a]

Q.279 In the final section of the electron beam gun, electron beam passes through the
electromagnetic lens and deflection coil.
a True b False [Ans. : a]

Q.280 What is the purpose of a series of slotted rotating discs provided between the electron
beam gun and the workpiece ?
a It increases the accuracy of the beam
b It can increase the intensity of the beam (if needed)
c It prevents power losses
d It prevents vapour generated during machining to reach the gun [Ans. : d]

Q.281 For alignment of the beam, is provided.

a a lens b a telescope
c magnifier d microscope [Ans. : b]

Q.282 The workpiece is mounted on a CNC table.

a True b False [Ans. : a]

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Q.283 Level of vacuum within the gun is in the order of .

–4 –6
a 10 to 10 Torr b 10– 1 to 10– 3 Torr
c 10–.0.65 to 10– 1 Torr d 1 to 2 Torr [Ans. : a]

Q.284 In electron beam gun, vacuum is achieved by .

a reciprocating pump b rotary pump only
c combination of rotary pump and diffusion pump
d combination of diffusion pump and vane pump [Ans. : c]

Q.285 Diffusion pump is an .

a oil filter equipment b oil heater
c oil cooler d oil collector [Ans. : b]

Q.286 The oil coming out of diffusion pump is evacuated by a .

a screw pump b gear pump
c rotary pump d piston pump [Ans. : d]

Q.287 High velocity gets of oil vapour coming out of diffusion pump entrain present
within the gun.
a water droplets b oil droplets
c air molecules d hazardous gas molecules [Ans. : b]

Q.288 Which of the following parameters do not affect the electron beam machining process ?
a Accelerating voltage b Lens current
c Spot size d Workpiece material [Ans. : d]

Q.289 For the electron beam machining process, pulse duration for the electron beam is in
range of .
a 10 μs to 90 μs b 50 μs to 15 ms
c 80 μs to 10 ms d 15 ms to 1 s [Ans. : b]

Q.290 Beam current is in the range of .

a 50 μamp to 0.8 amp b 100 μamp to 10 amp
c 200 μamp to 1 amp d 185 μamp to 1.5 amp [Ans. : c]

Q.291 Increasing the beam current directly increases the .

a energy per pulse b accelerating voltage
c spot size d lens current [Ans. : a]

Q.292 In electron beam machining process, the energy density is controlled by spot size.
a True b False [Ans. : a]

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Q.293 At higher energy densities, material removal rate is high.

a True b False [Ans. : a]

Q.294 In electron beam machining, the plane of is on the surface of the workpiece.
a focusing b finishing
c heating d drilling [Ans. : a]

Q.295 can manoeuvre the electron beam.

a Nozzles b Magnetic lens
c Electromagnetic coils d Deflector coils [Ans. : d]

Q.296 Electron beam machining process can machine holes of diameters in the range of
a 10 μm to 80 μm b 50 μm to 100 μm
c 100 μm to 2 mm d 2 mm to 5 mm [Ans. : c]

Q.297 Which of the following is true about electron beam machining (EBM) ?
a By EBM process, tapered holes can be generated
b Electro-magnetic coils are used to change the direction of the electron beam
c Electron beam gun works under high pressure
d Increasing the current density increases the spot size [Ans. : a]

Q.298 Which of the following holds true for electron beam machining ?
a This process does not generate burr
b Holes having length/diameter ratio as high as 50 can be machined by this process
c In electron beam gun, magnetic lens is used to diverge the beam
d Electron beam is accelerated by electromagnetic coils [Ans. : a]

Q.299 Which of the following materials is not machined by the EBM process ?
a Titanium b Wood
c Plastic d Leather [Ans. : b]

Q.300 For EBM process, heat affected zone is about

a 10 μm to 80 μm b 20 μm to 30 μm
c 100 μm to 1 mm d 2 mm to 5 mm [Ans. : b]

Q.301 Which of the following materials are easy to a machine by EBM process ?
a Aluminium b Steel
c Plastic d Wood [Ans. : a]

Q.302 Number of holes drilled per second depends on the holes diameter.
a True b False [Ans. : a]

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Q.303 While machining, there are chances of thermal damage associated with EBM.
a True b False [Ans. : a]

PLASMA ARC MACHINING

Q.304 What is the full form of PAM in the advanced machining processes ?
a Plasma Arc Manufacturing b Plasma Arc Machining
c Plasma Active Manufacturing d Plasma Active Machining [Ans. : b]

Q.305 When the Plasma Arc machining process came into the industrial world ?
a 1920s b 1930s
c 1950s d 1970s [Ans.: c]

Q.306 PAM is the only process which works faster in steel than steel.
a stainless, mild b mild, stainless
c remains same all d all of the mentioned [Ans. : a]

Q.307 What is the temperature reached by cathode in order to produce plasma arc ?
a 12000 ºC b 18000 ºC
c 28000 ºC d 40000 ºC [Ans. : c]

Q.308 What is the value of velocity of plasma jet in plasma arc machining ?
a 100 m/sec b 300 m/sec
c 400 m/sec d 500 m/sec [Ans. : d]

Q.309 What is the value of material removal rate in plasma arc machining process ?
a 50 cm3/min b 100 cm3/min
c 150 cm3/min d 200 cm3/min [Ans. : c]

Q.310 What is the value of specific energy used in Plasma arc machining process ?
a 100 W/(cm3-min) b 200 W/(cm3-min)
c 300 W/(cm3-min) d 400 W/(cm3-min) [Ans. : a]

Q.311 What is the value of the power used in PAM process ?

a 0.1 - 10 kW b 2 - 200 kW
c 200 - 400 kW d 400 - 700 kW [Ans. : b]

Q.312 What is the value of the voltage used in PAM process ?

a 0.1 - 20 V b 30 - 250 V
c 300 - 400 V d 500 - 600 V [Ans. : b]

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Q.313 What is the value of the current used in PAM process ?

a Up to 200 A b Up to 400 A
c Up to 600 A d Up to 800 A [Ans. : c]

Q.314 What is the value of machining speed used in PAM process ?

a 0.1 - 7.5 m/min b 8.5 - 10.5 m/min
c 15.5 - 19.5 m/min d 20.5 - 25.5 m/min [Ans. : a]

Q.315 What is the maximum value of the thickness used in PAM process ?
a 100 mm b 200 mm
c 300 mm d 400 mm [Ans. : b]

Q.316 Which of the following are the different shielded plasmas used in PAM ?
a Gas-shielded plasma b Water-shielded plasma
c Gas-shielded & Water-shielded plasma d None of the mentioned [Ans. : c]

Q.317 Material removal rates depend on which of the following factors ?

a Work piece material b Type of cutting
c Shielding gases d All of the mentioned [Ans. : d]

Q.318 A low power factors indicates energy required and removal

rates.
a low, low b low, high
c high, low d high, high [Ans. : b]

Q.319 What happens to the machining speed if the thickness of material is increased in PAM ?
a Decreases b Increases
c Enhanced d Remains same [Ans. : a]

Q.320 What is the machining speed required for machining of 12 mm thick plate with 220 kW
energy ?
a 1000 mm/min b 1500 mm/min
c 2000 mm/min d 2500mm/min [Ans. : d]

Q.321 How much distortion is produced while machining using PAM ?

a 10 % b 20 %
c 30 % d No distortion is produced [Ans. : d]

Q.322 The cut edge of the material tends to be than the base metal in PAM.
a smoother b harder
c same as d none of the mentioned [Ans. : b]

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Q.323 What is the thickness of the HAZ in PAM ?

a 0.001 to 0.23 mm b 0.25 to 1.12 mm
c 1.3 to 2.56 mm d 2.73 to 5.26 mm [Ans. : b]

Q.324 How much thickness of cracks may arise beyond HAZ due to rapid cooling ?
a 1.6 mm b 2.6 mm
c 3.6 mm d 4.6 mm [Ans. : a]

Q.325 What are the values of tolerances obtained by using PAM ?

a ± 0.6 mm b ± 1.6 mm
c ± 2.6 mm d ± 3.6 mm [Ans. : b]

Q.326 What is the maximum thickness of the walls of tube machined using plasma arc ?
a 10 mm b 30 mm
c 50 mm d 70 mm [Ans. : c]

Q.327 Which of the following are the advantages of PAM ?

a No chemical b Less harmful
c Operates cleanly d All of the mentioned [Ans. : d]

Q.328 Which of the following chemicals are used in PAM ?

a Harmful chlorinated fluorocarbons b Acid cleaning chemicals
c Dissolvable solvent chemicals d None of the mentioned [Ans. : d]

Q.329 How much amount of energy is required for machining using PAM ?
a Low b Moderate
c High d Very high [Ans. : a]

Q.330 What are the disadvantages of PAM?

a Large power supplies b Heat produced
c Toxic fumes produced d All of the mentioned [Ans. : d]

Thermal and Electrical Energy Based Processes ends …

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 Phase Diagrams

Syllabus : Chemical machining and Electro-Chemical machining (CHM and ECM)-

Etchants - Maskant - techniques of applying maskants - Process Parameters - Surface finish
and MRR-Applications. Principles of ECM – equipments - Surface Roughness and MRR
Electrical circuit-Process Parameters ECG and ECH - Applications.

Section No. Topic Name Page No.

3.1 Chemical Machining 3-2

3.2 Electrochemical Machining 3-8

3.3 Electro Chemical Grinding (ECG) 3 - 14

3.4 Electro Chemical Honing (ECH) 3 - 18

3.5 Two Marks Questions with Answers (Part - A) 3 - 22

3.6 Long Answered Questions (Part - B) 3 - 22

3.7 Multiple Choice Questions with Answers 3 - 23

 Chemical and Electro-Chemical Energy Based Processes

3.1 Chemical Machining

• This process is one of the old material removal processes which employ chemicals for
the material removal.
• Nearly all metals and even ceramics can be machined.
• The CHM process is employed where metal removal is difficult or impractical by the
conventional machining process.
• In this process, is used for the production are protected from chemical attack by
masking.
• This process is used for the production of printed circuit boards (PCB’s), engraving,
machining of air crafts etc.,

Definition
• CHM is a material removal process used for the production of the required shape and
dimensions through selective or overall material removal by controlled chemical attack
with acid or alkalis.
• CHM process can be classified into two types
i) Chemical Milling ii) Chemical blanking

i) Chemical Milling
• Chemical milling is defined as the process of chemically eroding material to produce
“blind” details like pockets, channels, etc.

ii) Chemical Blanking

• This is the process chiefly used for producing details that penetrate material entirely
(Holes, Slots etc.,) or to blank complete parts from sheet material by chemically etching
the periphery of the desired shape.
• Processing steps for chemical machining

Preparation of work material Pre cleaning

Masking Application of chemically resistant material on the places where

machining is not required

Etching To dip or spray exposing the marked material to the reactive

environment or etchant

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 Chemical and Electro-Chemical Energy Based Processes

Removal of mask The maskant applied on the un machined areas are removed and then
the work material is cleaned.

Finish If further process is required, do it or inspect and post process it.

3.1.1 Equipment
• The equipment consists of a tank or container filled with the etchant.
• The work material is either suspended by a hanger or set on a table inside the tank.
• A stirrer is fitted in the tank to ensure uniform etching.
• A heater is also attached inside the tank to accelerate the etching process.
• To ensure uniform material removal, the etchant continuously sprayed onto the part or
the part is submerged in the tank of agitated etchant.
• However, too much agitation should be avoided, since it causes areas of cavitation or
stagnation which results in ridges, waviness or grooves in the etched surface.

Fig. 3.1

3.1.2 Five Step Process of Chemical Machining

i) Cleaning ii) Masking ii) Scribing
iii) Etching iv) Demasking

i) Cleaning
• The materials to be machined first cleaned thoroughly to effect uniform adhesion of the
maskant and uniform chemical dissolution of the metals.
• Proper cleaning lowers the maskant debonding.

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 Chemical and Electro-Chemical Energy Based Processes

• Depending upon the type of maskant, the required depth of cut and the work piece
material the cleaning operation vary from simple solvent to high degree cleaning of
operations such as flash etching, vapor degreasing or alkaline etching.
• The porous materials present difficulties for the cleaning process because entrapment of
unwanted particles and cleaning solutions.
• When cleaning Aluminium, Magnesium, Steel or titanium alloys the industries adopt the
following cleaning process.
i) Vapour degreasing
ii) Alkaline cleaning
iii) Deoxidizing, after cleaning the parts are dried.

ii) Masking
• The chemically resistant mask is applied on the workpiece material by either dip flow
coat, airless spray techniques or brushing depends on the part size and configurations.
• Two or more coatings are applied to Aluminium and Magnesium parts while four or
more applied to steel, titanium,

iii) Maskants
• Masking material which is called maskant is used to protect workpiece surface from
chemical etchant. Polymer or rubber based materials are generally used for masking
procedure.
• The selected maskant material should have following properties.
▪ Tough enough to withstand handling
▪ Well adhering to the workpiece surface
▪ Easy scribing
▪ Inert to the chemical reagent used
▪ Able to withstand the heat used during chemical machining
▪ Easy and inexpensive removal after chemical machining etching.
• Multiple maskant coatings are used to provide a higher etchant resistance. Long
exposure time is needed when thicker and rougher dip or spray coatings are used.
• Various maskant application methods can be used such as dip, brush, spray, roller, and
electro coating as well as adhesive tapes.
• When higher machined part dimensional accuracy is needed, spraying the mask on the
workpiece through silk screen would provide a better result.

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 Chemical and Electro-Chemical Energy Based Processes

• Thin maskant coating would cause severe problems such as notwithstanding rough
handling or long exposure times to the etchant.
• The application of photo resist masks which are generally used in photochemical
machining operation, produce high accuracy, ease of repetition for multiple part etching,
and ease of modification.
• Possible maskant materials for different workpiece materials were given in Table.
• Masking materials for vaious chemical machined materials
Workpiece material Masking material

Aluminium and alloys Polymer, Butyl rubber, neoprene

Iron based aloys Polymer, polyvinyl chloride, polyetilien

butyl rubber

Nickel Neoprene

Magnesium Polymer

Copper and alloys Polymer

Titanium Polymer

Silicon Polymer

iv) Scribing
• After the application of maskant on the workpiece material the required areas are to be
machined are scribed by using knife.
• Patterns and templates are used for obtaining the required shape of the area to be
machined chemically.
• Epoxy-impregnated fibre glass, Aluminium, steel are commonly used templates.
• The blank part is scribed with the desired pattern as determined by template.
• After the part is scribed, the maskant in the scribed area is peeled off, leaving the areas
for etching.
• Time of immersion of the workpiece in the etchant is determine the depth of cut.

v) Etching
• The etching of the work material done by adopting immersion or spraying technique.
• The etching is done until required depth of cut is obtained.
• Step etching is done by repeated cycles of masking and peeling off.
• Also the pans are rotated during the cycle to ensure uniform etching.

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 Chemical and Electro-Chemical Energy Based Processes

3.1.3 Etchant
• The purpose of etchant is to dissolve the workpiece material by turning it into a metallic
salt, which goes into the solution.
• Etchants are the most influential factor in the chemical machining of any material.
Various etchant are available due to workpiece material. The best possible etchant
should have properties as follows
▪ High etch rate
▪ Good surface finish
▪ Minimum undercut
▪ Compatibility with commonly used Maskants
▪ High dissolved-material capacity
▪ Economic regeneration
▪ Easy control of process.
▪ Personal safety maintenance
Etchant Selection

Required Surface finish Some combination of material and etchant result in the formation of
surface oxide, which degrade the finish

Removal rate Faster rates lower the cost, but attack the resist bond, result in poor
finish or producing high heat

Material type Etchant must attack the material without causing embrittlement or
corrosion cracking

Etch depth Some etchants produce surface finishes that worsen with increasing
depth

Type of resist Etchant must destroy resist during the process time.

Cost Cost of the etchant, maintenance and disposal must be considered

3.1.4 Demasking
• Final step is to remove masking material from etched part. The inspections of the
dimensions and
• Surface quality are completed before packaging the finished part.

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 Chemical and Electro-Chemical Energy Based Processes

Method of Masking
Masking can be achieved by any of the following process
▪ Cut and peel
▪ Photographic resist
▪ Screen resist

Cut and Peel

• Apply maskant over entire part by dipping, spraying or painting.
• Maintain the maskant thickness as 0.025 mm to 0.125mm
• After the machining process, maskant can be removed by hand or using knife.
• This type of technique mostly employed in where the accuracy is not important.

Photographic Resist
• In this method photographic technique is used for masking.
• The maskant material contain photo sensitive materials.
• This process is normally applied where small parts are produced in high quantities and
close tolerances are required.

Screen Resist
• The maskant is applied by means of silk screening method.
• Maskant is painted on the work parts surface through a silk or steel mesh.
• This method is usually adapted where the accuracy is moderate.
• Tolerance ± 0.075 mm can be achieved with this masking method.

3.1.5 Advantages
The application of chemical machining provides several advantages as follows
• Easy weight reduction
• No effect of workpiece materials properties such as hardness
• Simultaneous material removal operation
• No burr formation
• No stress introduction to the workpiece
• Low capital cost of equipment
• Easy and quick design changes
• Requirement of less skilled worker
• Low tooling costs

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 Chemical and Electro-Chemical Energy Based Processes

• The good surface quality

• Using decorative part production
• Low scrap rates (3 %).

3.1.6 Disadvantages
• Difficult to get sharp corner
• Difficult to chemically machine thick material (limit is depended on workpiece material,
but the thickness should be around maximum 10 mm)
• Scribing accuracy is very limited, causes less dimensional accuracy
• Etchants are very dangerous for workers
• Etchant disposals are very expensive

3.1.7 Environmental Issues in Chemical Machining

Environmental issues in chemical machining operations may be the most important factor
affects the machining process should be used or not. Most of the chemicals such as cleaning
solutions, etchants, strippers etc. are very hazardous liquids. Therefore handling and disposal
of them are very costly. Industrial trend of using these chemicals are to select more
environmentally accepted ones for chemical machining process. Moreover, regeneration of
waste etchant and etched metal recovery from waste etchants have been studied and there
could be a suitable regeneration/recovery systems for some etchants like FeCl3, CuCl2 and
alkaline etchants.

3.2 Electrochemical Machining

• Electrochemical Machining (ECM) is a non-traditional machining (NTM) process
belonging to Electrochemical category.

• It is a method of removing metal by an electrochemical process. It is best suited for the

metals and alloys which are difficult to machine by conventional process.
• It can able to cut intricate shapes even in hard metals like titanium aluminides, Inconel,
waspalloy etc., both external and internal surfaces can be machined.
• ECM is a anodic dissolution of atomic level of work piece that is electrically conductive
by a shaped tool due to flow of high current through electrolyte.

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 Chemical and Electro-Chemical Energy Based Processes

Fig. 3.2 Schematic principle of Electro Chemical Machining (ECM)

3.2.1 Principle
This process based on Faraday’s Law of electrolysis
1. First law states that the amount of any material dissolve or deposited is proportional
to the quantity of electricity passed.
2. Second law states that, the amount of change produced in the materials is
proportional to its electrochemical equivalent of the materials.
• ECM is the reverse electroplating method.
ECM Electroplating

Material removed from the work piece Metal deposited on the work piece

Workpiece connected to positive terminal Work piece is connected to negative

and the tool is connected to negative terminal and the tool is connected to
terminal. positive terminal.

When the current passed the work piece Tool loses material and the metal deposited
loses metal and the dissolved metal is on the work piece.
carried out by circulating an electrolyte
between work and tool

3.2.2 Construction and the Working of ECM Process

• Electrochemical machining (ECM) is a machining process in which electrochemical
process is used to remove materials from the workpiece. In the process, workpiece is
taken as anode and tool is taken as cathode.
• The two electrodes workpiece and tool is immersed in an electrolyte (such as NaCl).
• When the voltage is applied across the two electrodes, the material removal from the
workpiece starts.
• The workpiece and tool is placed very close to each other without touching.

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 Chemical and Electro-Chemical Energy Based Processes

• In ECM the material removal takes place at atomic level so it produces a mirror finish
surface.
• This process is used to machine only conductive materials.
• ECM working is opposite to the electrochemical or galvanic coating or deposition
process.
• During electrochemical machining process, the reactions take place at the electrodes i.e.
at the anode (workpiece) and cathode (tool) and within the electrolyte.
• Let’s take an example of machining low carbon steel which is mainly composed of
ferrous alloys (Fe).
• We generally use neutral salt solution of sodium chloride (NaCl) as the electrolyte to
machine ferrous alloys.
• The ionic dissociation of NaCl and water takes place in the electrolyte as shown below.
+ –
NaCl → Na + Cl
+ –
H2O → H + OH
• As the potential difference is applied across the electrode, the movement of ions starts in
between the tool and w/p. The positive ions moves towards the tool (cathode) and
negative ions move towards the workpiece.
• At cathode the hydrogen ions takes electrons and gets converted into hydrogen gas.
+ –
2H + 2e → H2 

• In the same way the iron atoms comes out from the anode (w/p) as Fe++ ions.
++ –
Fe → Fe + 2e
• Within the electrolyte, the sodium ions combines with Hydroxyl ions and form sodium
hydroxide and ferrous ion combine with Chloride ions and forms ferrous chloride. Also
iron ions combine with hydroxyl ions and forms Iron hydroxide.
+ –
Na + OH → NaOH
2+ –
Fe + 2Cl → FeCl2 

• In the electrolyte the FeCl2 and Fe(OH) 2 produced and gets precipitated in the form of
sludge and settle down. In this way material is removed from the workpiece as sludge.
• The various reactions taking place in the Electrochemical machining process are in the
figure given below

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 Chemical and Electro-Chemical Energy Based Processes

Fig. 3.3 Chemical reaction of ECM

3.2.3 Main Equipment of ECM

• The ECM system has the following modules
▪ Power supply
▪ Electrolyte filtration and delivery system
▪ Tool feed system
▪ Working tank

Fig. 3.4 Schematic diagram of ECM

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3.2.4 Working Process of Electrochemical Machining

• First the workpiece is assembled in the fixture and tool is brought close to the
workpiece. The tool and workpiece is immersed in a suitable electrolyte.
• After that, potential difference is applied across the w/p (anode) and tool (cathode). The
removal of material starts. The material is removed as in the same manner as we have
discussed above in the working principle.
• Tool feed system advances the tool towards the w/p and always keeps a required gap in
between them. The material from the w/p is comes out as positive ions and combine
with the ions present in the electrolyte and precipitates as sludge. Hydrogen gas is
liberated at cathode during the machining process.
• Since the dissociation of the material from the w/p takes place at atomic level, so it
gives excellent surface finish.
• The sludge from the tank is taken out and separated from the electrolyte. The electrolyte
after filtration again transported to the tank for the ECM process.

3.2.5 Parameters in ECM

1) Metal Removal Rate (MRR) - It depends on the following factors :

(a) Current density
(b) Conductance of electrolyte
(c) Voltage applied
(d) Shape of electrodes
(e) Gap between the tool and workpiece.

2) Electrolyte used - Following are the types of electrolyte used in the ECM process :
(a) Sodium chloride
(b) Sodium chromate
(c) Sodium hydroxide
(d) Potassium nitrate
(e) Sodium sulphate
(f) Potassium chloride
(g) Sodium fluoride
The electrolyte is used in the process for following purposes :
(a) It carries current between the tool and workpiece.

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(b) It flushes away the sludge and other contaminants from the machining area.
(c) It minimizes heat generated in the cutting zone due to current and chemical reaction.

3) Tool for ECM -

• The shape of the tool is reproduced on the workpiece, hence the tool face should be well
polished to obtain good surface finish on the workpiece. The tool used in the process
should have following properties :
(a) It should be good conductor of electricity.
(b) It should be easily machinable.
(c) It should have high chemical resistance.
(d) It should be easily available and cheap.
Most commonly used materials for ECM process are :
(a) Copper
(b) Brass
(c) Stainless steel
(d) Titanium

3.2.6 Applications
• The ECM process is used for die sinking operation, profiling and contouring, drilling,
grinding, trepanning and micro machining.
• It is used for machining steam turbine blades within closed limits.

3.2.7 Advantages
• Negligible tool wear.
• Complex and concave curvature parts can be produced easily by the use of convex and
concave tools.
• No forces and residual stress are produced, because there is no direct contact between
tool and workpiece.
• Excellent surface finish is produced.
• Less heat is generated.

3.2.8 Disadvantages
• The risk of corrosion for tool, w/p and equipment increases in the case of saline and
acidic electrolyte.

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• Electrochemical machining is capable of machining electrically conductive materials

only.
• High power consumption.
• High initial investment cost.

3.2.9 Process Capabilities

S. No. Parameters Values

1. Power supply

Type Direct Current

Voltage 2 to 35 V

Current 50 to 40,000 A
2 2
Current Density 0.1 A/mm to 5 A/mm

2. Electrolyte

Material NaCl and NaNO3

Temperature 20 C to 50 C

Flow rate 20 lpm/100 A current

Pressure 0.5 to 20 bar

Dilution 100 g/l to 500 g/l

3. Working gap 0.1 mm to 2 mm

4. Overcut 0.2 mm to 3 mm

5. Feed rate 0.5 mm/min to 15 mm/min

6. Electrode material Copper, brass and bronze

7. Surface roughness (Ra) 0.2 to 1.5 μm

3.3 Electro Chemical Grinding (ECG)

• ECG is the material removal process in which the material is removed by the
combination of Electro-chemical deposition as in ECM process and abrasion due to
grinding.

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Process :
• ECG is a combination of ECM and the grinding process. The metal is removed by both
anodic dissolution as in ECM and abrasion by the grinding wheel.
• Conventional grinding of carbides, high strength temperature resistant alloys and hard to
machine alloys become very costly because of employing the high cost abrasives and
diamond wheels.
• The possibility of cracking in the grinding wheels due to the abrasion of hard materials
is eliminated in the ECG process.
• Hard and difficult to machine, fragile, and electrically conductive materials can be easily
machined by ECG process. In this process, 10 % of the work material is removed by
abrasive cutting and 90% by electrolytic action.

Fig. 3.5 ECG process

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3.3.1 Equipment
• The equipment consists of a conductive grinding wheel rotated by an insulated spindle,
an electrolyte spraying and circulating unit and a work table for achieving desired shape
and size of machining.
• Also a DC power supply unit is employed for the supply of electrical energy. At the
outset, the ECG equipment is similar to a conventional grinder.
• The grinding wheels used in ECG process are conductive ones. It consists of abrasive
particles in an electrically conductive bonding agent.
• Copper, Brass, Nickel are the most commonly used materials for metal-bond
wheels. Soft, copper-impregnated resins are used when wheels are fabricated for form-
Grinding applications.
• The most common abrasive used is Aluminium oxide. In special applications, a solid
metal disk with a layer of diamond particles, in a nickel matrix is used.
• The abrasive particles of the grinding wheel are non-conductor of electricity. The
abrasive grits on the grinding wheel are made to protect from 0.0125 mm to 0.0375 mm
from the surface of the grinding wheel.
• The grinding wheels are dressed in the conventional way using a diamond dresser.
Several techniques are employed to maintain the proper gap between the wheel and
workpiece during machining.
• The grinding wheel and the spindle are insulated from the rest of the machine. The short
circuit between the wheel and the work piece is prevented due to point contact made by
the fine diamond points.
• Two methods are currently employed to carry power through the spindle, the brushes
and mercury couplings.
• Most of the ECG machines use heavy metal brushes to provide sliding electrical
connection. But the use of brushes is limited because of its inability to carry high
current. The mercury couplings are used to carry high current and ensure for higher
material removal.
• The electrolyte system consists of pump, filter, Relief valve etc., the electrolyte is
pumped in the gap between the work and the grinding wheel.
• The used electrolyte contacting the removed material and sludges are collected in the
reservoir from which it passes through the filter and is pumped to the machining area
through flow control and relief valve.

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• The feeding mechanism is attached to the machine table provides the feed to the
workpiece.

3.3.2 Working Principle

• The workpiece is made as anode which is connected to the positive terminal of the DC
power supply and the grinding wheel tool is made as the cathode.
• A small gap of approximately 0.025m is maintained between the work surface and
grinding wheel.
• A suitable electrolyte is fed into the gap through nozzle. When a low voltage of 4 to 15
volts and current of 100 amps is applied between the tool and the workpiece.
• A high density current (77 to 620 amp/cm2) passes through them.
• The whole system forms an electrolytic cell and hence machining occurs by,
a) Anodic dissolution of the workpiece.
b) Abrasive action of the grits of the wheel.
When voltage is applied, the work material gets dissolved in the electrolyte and as the
wheel rotates, the abrasive particle remove the material by abrasive action.

Material Removal Rate

The material removal rate in electrochemical Grinding can be calculated from the equation,
MI
MRR =
F
M is equivalent weight in grams
I is the current in ampere
ρ is density g/mm3
F faradays constant in coulomb

3.3.3 Advantages
1. No thermal damage to the work piece.
2. About 80% faster material removal rate than conventional grinding
3. Long lasting wheels because 10% grinding action by grits.
4. Wheel wear is negligible.
5. No distortion of the workpiece.
6. No micro-crack and no structural changes occur in the workpiece.
7. Cutting force is very small compared to conventional grinding.

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8. Higher accuracy is achieved. (about 0.01mm)

9. Single pass grinding.
10. More economical for grinding harder material than conventional grinding.

3.3.4 Disadvantages
1. High capital costs, Because of the special tool and insulation arrangements.
2. Power consumption is quite high.
3. Electrolyte is corrosive.
4. The electrolyte and the bonding material should have high electrical conductivity.
5. High Preventive maintenance costs.

3.3.5 Limitations
1. The work material must be conductive.
2. Not suitable for machining soft materials.
3. Require dressing tools for preparing the wheels.

3.3.6 Applications
1. Precision grinding of hard metals economically.
2. Grinding carbide cutting tool inserts.
3. To Re-profile motor gears, gear teeth and re-establish new teeth contour.
4. Burr-free sharpening of hypodermic needles, grinding of super alloy turbine blades
and form grinding of fragile honeycomb metals.
5. To grind end mill cutters more precisely.
6. Thin walled components of hard steels can be easily and accurately ground by this
process.

3.4 Electro Chemical Honing (ECH)

• Electro Chemical Honing process comes under the process of Electro Chemical
Machining process. It is the usage of combined power of electricity and chemical energy
for the material removal from the work piece is known as Electro Chemical Machining
process.
• Electro Chemical Honing process is mostly employed for better surface finish, accuracy
and economic aspects too.

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• Honing is an abrasive machining process that produces a precision surface on a metal

workpiece by scrubbing an abrasive stone against it along a controlled path.
• Honing is primarily used to improve the geometric form of a surface, but may also
improve the surface texture.
• A special tool, called a honing stone or a hone, is used to achieve a precision surface.
• The hone is composed of abrasive grains that are bound together with an adhesive.
• Generally, honing grains are irregularly shaped and about 10 to 50 micrometers in
diameter (300 to 1,500 mesh grit).
• Smaller grain sizes produce a smoother surface on the workpiece.
• Hone tool has a combined motion of rotation and translation
• A honing stone is similar to a grinding wheel in many ways, but honing stones are
usually more easily crumbled so that they conform to the shape of the workpiece as they
wear in.
• To counteract their friability, honing stones may be treated with wax or sulfur to
improve life; wax is usually preferred for environmental reasons.
• Any abrasive material may be used to create a honing stone, but the most commonly
used are corundum, silicon carbide, cubic boron nitride, or diamond.

Fig. 3.6 Structure of hone tool

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 Chemical and Electro-Chemical Energy Based Processes

• In an electrochemical honing process, in order to obtain better accuracy, the size of the
tolerance on the diameter can be provided at 0.01 mm and roundness can be maintained
at lesser than 0.05 mm.
• It provides the surface roughness in the range of 0.1 microns to 0.5 microns. To attain a
specified roughness on the work surface, the abrasive honing stones are required to keep
on the work for a few seconds after the power is cut off.
• The surface finish of the electrochemical honing process obtained is mostly based up on
the following terms.
1. Size of the abrasive grains.
2. Speed of the rotation and reciprocation.
3. Duration of the run out period.

Fig. 3.7
3.4.1 Process Characteristics
• Abrasive stones are used to maintain the gap size of 0.075 to 0.250 mm.
• Surface finish ranges from: 0.2 to 0.8 μm.
• Electrolyte temperature is nearly maintained at 38-40 C.
• Pressure of 1000 kPa.
• Flow Rate : 95 L/min.
• DC current is used.
• Voltage gap of 6 to 30 V is kept accordingly.
• Current density of 465 A/cm2 .
• Cross-hatched cut surface is obtained after machining which is most desired after any
load bearing surface.

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 Chemical and Electro-Chemical Energy Based Processes

• Tolerance can be achieved is as low as ±0.003 mm.

• Material removal rate is 3 to 5 times faster than conventional honing and 4 times faster
than that of internal cylindrical grinding.

3.4.2 Advantages of Electorchemical Honing Process

1. Electrochemical honing process enhances the material removal rate specifically for
harder materials.
2. There is no presence of burrs on the finished surfaces.
3. Electrochemical honing process requires minimum amount of work pressure on the
tool and the work piece.
4. Electrochemical honing process reduces the noise level and distortion while honing
thin walled tubes.
5. Electrochemical honing process increases the accuracy without damaging the
materials due to the provision of cooling medium.

3.4.3 Disadvantages
• Machinery cost is high
• Machining cost per piece increases as it is an addition process.

3.4.4 Applications
• Due to rotating and reciprocating honing motion, the process reduces the errors in
roundness through the rotary motion.
• Taper and waviness errors can also be reduced

Fig. 3.8 Removing roundness error

• Typical applications are the finishing of cylinders for internal combustion engines, air
bearing spindles and gears.

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3.5 Two Marks Questions with Answers (Part - A)

Q.1 What are the advantages of chemical machining ? (Section 3.1.5)
Q.2 What are the factors influencing the selection of maskants in chemical machining
process ? (Section 3.1.2 (iii))
Q.3 What are maskants in chemical machining process ? (Section 3.1.2 (iii)Table)
Q.4 Write the principle of Electro Chemical Machining (ECM) ? (Section 3.2.1)
Q.5 Name any two electrolytes used in ECM. (Section 3.2.5 (2))
Q.6 What are the materials used for tools in ECM ? (Section 3.2.5 (3))
Q.7 What are the process parameters of ECM ? (Section 3.2.5 (1))
Q.8 What is the function of electrolyte in ECM ? (Section 3.2.5 (2))
Q.9 Mention the applications of ECM. (Section 3.2.6)
Q.10 Mention a few advantages of ECM process. (Section 3.2.7)
Q.11 What is the basic difference between electro plating and ECM ?
(Section 3.2.1 (Table))
Q.12 State the working principle of ECG. (Section 3.3.2)
Q.13 State the advantages of ECG. (Section 3.3.3)
Q.14 Give the applications of Electro Chemical Honing (ECH) process. (Section 3.4.4)
Q.15 Write any two process characteristics of ECH ? (Section 3.4.1)

3.5 Long Answered Questions (Part - B)

Q.1 Describe the working principle and elements of chemical machining.
(Section 3.1.1)
Q.2 Briefly explain the following with respect to chemical machining. (Section 3.1.2)
a. Characteristics of cut and peel maskants
b. Selection of maskants
c. Advantages of photoresist maskant
d. Limitations of chemical machining.
Q.3 List the advantages of chemical machining process. (Section 3.1.5)
Q.4 Why maskants are required in chemical machining process ? Explain.
(Section 3.1.2 (iii))
Q.5 During the machining of Iron (Fe) using aqueous solution of Nacl, what are the
possible reactions at electrodes ? (Section 3.2.2)
Q.6 Explain the ECM process. Explain how a replica of the tool is obtained.
(Section 3.2)
Q.7 Explain in detail ECM process with sketch and also mention the advantages and
application. (Sections 3.2.4 , 3.2.6 and 3.2.7)

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Q.8 Explain the process of electro chemical machining with a neat sketch and discuss
about influences of process parameters in machining output. (Section 3.2.5)
Q.9 Describe the principle of ECG and ECH. Discuss about the process parameters that
influences the ECM. (Sections 3.3 and 3.4)
Q.10 Explain the working principle of Electro Chemical Grinding (ECG) and discuss the
process capabilities and application. (Section 3.3)
Q.11 Explain the principle of ECG with sketch. (Sections 3.3.1 and 3.3.2)
Q.12 Describe the Electro Chemical Honing (ECH) process with a neat sketch.
(Section 3.4)

3.7 Multiple Choice Questions with Answers

Chemical Machining

Q.1 In advanced machining processes, what is the full form of CHM ?

a Chemical machining b Chemical manufacturing
c Chemical machining d None of the mentioned [Ans. : a]

Q.2 Of the following, which mechanism is used for the removal of material using chemical
machining process ?
a Material vaporization b Chemical dissolution
c Mechanical erosion d Mechanical abrasion [Ans. : b]

Q.3 Which of the following solutions cannot be used as chemical reactive solution in CHM ?
a Acidic solution b Alkaline solution
c Neutral solution d None of the mentioned [Ans. : c]

Q.4 By using chemical machining, which of the following can be produced ?

a Pockets b Contours
c Slots d All of the mentioned [Ans. : d]

Q.5 Pre cleaning is done on the work piece surface in order to achieve, which of the
following factors ?
a To provide good adhesion b To provide clean surface
c To assure the absence of contaminants d All of the mentioned [Ans. : d]

Q.6 Special coatings applied on work piece materials in order to protect them from chemical
reaction are known as .
a maskants b protective coverings
c protective varnishing d none of the mentioned [Ans. : a]

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Q.7 Type of mask depends on which of the factor/s, given below ?

a Size of work piece b Number of parts
c Desired resolution d All of the mentioned [Ans. : d]

Q.8 During chemical machining, depth of etch is controlled by which factor of immersion ?
a Time b Mask method
c Mask area d None of the mentioned [Ans. : a]

Q.9 What is the range of reagent temperatures used for chemical dissolution in CHM ?
a 12 ºC to 35 ºC b 37 ºC to 85 ºC
c 90 ºC to 101 ºC d 121ºC to 142 ºC [Ans. : b]

Q.10 In chemical machining, excessive flow of chemical reagent results in which of the
following defects ?
a Channellings b Grooves
c Ridges d All of the mentioned [Ans. : d]

Q.11 State whether the following statement about chemical machining is true or false.
“At higher temperatures, faster etching rates occur in chemical machining.”
a True b False [Ans. : a]

Q.12 Of the following, which ratio defines the etch factor ?

a Etching depth to undercut b Undercut to etching depth
c Undercut to mask area d Mask area to undercut [Ans. : b]

Q.13 CHM cannot eliminate which of the following defects ?

a Irregularities and dents b Surface scratches
c Waviness d All of the mentioned [Ans. : d]

Q.14 Which of the following are the tools required for chemical machining ?
a Maskants b Etchants
c Scribing plates d All of the mentioned [Ans. : d]

Q.15 State which of the following statement is true or false regarding chemical machining.
“Maskants are generally used in CHM, to protect the work piece from the etching chemical
agent.”
a True b False [Ans. : a]

Q.16 Which of the following are the materials used for making maskants ?
a Synthetic materials b Rubber materials
c Polymeric materials d All of the mentioned [Ans. : d]

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Q.17 What are the properties that a maskant used in chemical machining should possess ?
a Be tough and adhere well b Scribe easily
c Be inert to chemical reagent d All of the mentioned [Ans. : d]

Q.18 Which of the following can be used to apply the maskants on work piece in chemical
machining ?
a Dipping or spraying b Rolling or electro coating
c Adhesive tapes d All of the mentioned [Ans. : d]

Q.19 State whether the following statement is true or false regarding maskants.
“After etching, maskants should be removed easily and inexpensively.”
a True b False [Ans. : a]

Q.20 In maskant application, photo-resist masks ensure which of the following advantages ?
a High accuracy b Ease of repetition
c Ease of modification d All of the mentioned [Ans. : d]

Q.21 Which of the tolerance values are obtained, when we use cut and peel mask method for
maskant ?
a ± 0.013 mm b ± 0.045 mm
c ± 0.077 mm d ± 0.179 mm [Ans. : d]

Q.22 Which of the tolerance values are obtained, when we use silk-screen resist method for
maskant ?
a ± 0.013 mm b ± 0.045 mm
c ± 0.077 mm d ± 0.179 mm [Ans. : c]

Q.23 Which of the tolerance values are obtained, when we use photo resist method for
maskant application ?
a ± 0.013 mm b ± 0.045 mm
c ± 0.077 mm d ± 0.179 mm [Ans. : a]

Q.24 Which of the following, are the main uses of etchants applied in chemical machining ?
a Good surface finish b Uniform material removal
c Control intergranular attack d All of the mentioned [Ans. : d]

Q.25 State whether the following statement is true or false about etchants.
“Etchants are used for controlling H2 absorption in case of Ti alloys.”
a True b False [Ans. : a

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 Phase Diagrams

Syllabus : Abrasive flow machining, chemo-mechanical polishing, magnetic abrasive

finishing, magneto rheological finishing, magneto rheological abrasive flow finishing their
working principles, equipments, effect of process parameters, applications, advantages and
limitations.

Section No. Topic Name Page No.

4.1 Abrasive Flow Finishing (AFF) 4-2

4.2 Chemo Mechanical Polishing 4-5

4.3 Magnetic Abrasive Finishing (MAF) 4-7

4.4 Magneto Rheological Finishing 4 - 10

4.5 Magneto Rheological Abrasive Flow Finishing (MRAFF) 4 - 13

4.6 Multiple Choice Questions with Answers 4 - 16

 Advanced Nano Finishing Processes

4.1 Abrasive Flow Finishing (AFF)

• Now - a - days developments in the field of material science are taking place but at the
same time the demand for better quality and low cost products is also increases.
• There is a consistent demand for a decreased lead time from design to production.
• In a production cycle, finishing operations usually cost almost 15 % of the total cost.
Also, a need of automated finishing operations instead of manual is felt.
• Therefore, a non - traditional finishing process called as Abrasive Flow Machining
(AFM) or Abrasive Flow Finishing (AFF) has been developed.
• This method provides better accuracy and high efficiency, economically and
consistently.

Working principle :

• AFF is a kind of finishing process in which small quantity of material is removed by

flowing a semisolid abrasive slurry (putty) over the surface to be machined.

• The abrasive media has high viscosity. The common types of abrasives are aluminium
oxides (Al2O3), silicon carbide (SiC), cubic boron nitride and diamond dust.

• The process consists of two vertically opposed cylinders which extrude abrasive media
back and forth through the passage formed either by workpiece and tooling (fixture) or
by workpiece alone. Refer Fig. 4.1.

• This process is suitable for operations like deburring, radiusing, polishing, removing
recast layer, etc.

• The process can be used to machine multiple parts at the same time to increase the
productivity.

• Also, the machine has high flexibility i.e. the same machine can be used for different
workpieces by altering the toolings, machining parameters, media and abrasives.

• The semisolid abrasive media is forced through the workpiece (restricted passage)
formed by workpiece and tooling together.

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 Advanced Nano Finishing Processes

(a) (b)
Fig. 4.1 Working principle of AFF

• The force may be applied either hydraulically or mechanically. Also, the flow velocity
of media is governed by the cross-section area of passage.
• To maintain a constant viscosity of media, in some cases, coolers are also used to lower
the temperature of the media. Manual or computer control machines are also available.
• The basic purpose of tooling is to hold the parts in position and to contain the media and
direct its flow.
• As the process has low MRR (Material Removal Rate), the maximum machining takes
place wherever there is a maximum restriction to the flow of abrasive.
• Fig. 4.2 (a), (b) and (c) shows the finishing of internal surfaces.

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 Advanced Nano Finishing Processes

Fig. 4.2 Finishing of internal surfaces

• Fig. 4.3 shows the finishing of external surfaces in which the designer of tooling decides
the extent of restriction.

Fig. 4.3 Tooling for external surface to be finished

• After machining the parts should be cleaned properly by air or vacuum.

Process variables
• The important factors that affect the performance of the process and the quality of
product are as follows :
o Workpiece material (Hardness and composition)
o Machine and tooling (fixture design, cylinder size, clamping pressure, etc.)
o Geometry of component (passage shape, length, diameter, etc.)
o Media (Viscosity and its change during the process, flow rate, type and size of
abrasive, etc.)
o Adjustable parameters (Pressure and number of strokes)

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 Advanced Nano Finishing Processes

Applications :
• It is very useful for finishing of the following parts :
o Extrusion dies (improves die performance and life)
o Nozzle of flame cutting torch
o Airfoil surfaces of impellers of turbine
o Deburring of aircraft valve bodies and spools.
o Removing recast layer after EDM or LBM.
• It is used for finishing operations mainly in the industries related to the manufacturing of
aerospace, automotive, semiconductor, medical parts, etc.
• It also improves the mechanical fatigue strength of blades, disks, hubs, shafts, etc.

Advantages :
• By using AFF deburring, polishing and radiusing are conducted in one operation.
• This process can finish in accessible area.
• AFF is suitable for batch production.
• It is a very fast method.
• This method provides better accuracy and high efficiency.
• Media temperature control generally not required.
• Excellent process control and quick change tooling.

Disadvantages :
• Tooling or fixtures required are expensive.
• Initial cost of the machine is high.
• This process is not suitable for blind holes.

4.2 Chemo Mechanical Polishing

• Demands for high quality surface finish, dimensional and form accuracy are required for
optical surfaces and it is very difficult to achieve this using conventional grinding
methods.
• ELPD is new and efficient method that uses a metal bonded diamond grinding wheel to
achieve a mirror surface finish especially on hard and brittle materials.

Working principle :
• The basic elements of ELID grinding are shown in Fig. 4.4. ELID cell comprises of a
metal bonded grinding wheel, cathode electrode, DC power supply and electrolyte.

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Fig. 4.4 Basic elements of ELID grinding

• The grinding wheel is connected to the positive terminal of DC supply by a carbon

brush, whereas electrode is connected to the negative terminal of DC supply.
• Generally, alkaline liquids are used as electrolyte as well as coolant for grinding.
• An electrolyte is injected into the gap between the wheel and electrode by using a
nozzle. Usually, this gap is 0.1 to 0.3 mm.
• Due to electrochemical reaction an anodic oxide layer is formed on the circumference of
the grinding wheel.
• It is soft and brittle in nature as compared to original metal bond and easily gets worn
off because of the excessing grinding force.
• Fig. 4.5 shows the basic mechanism of ELID grinding.

Fig. 4.5 Basic mechanism of ELID grinding

• After truing, the grains and bonding material (metal) of the wheel surface are flattened.
Refer Fig. 4.5 (a).

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 Advanced Nano Finishing Processes

• For the trued wheel it is necessary to be electrically predressed to protrude the grains on
the wheel surface and the dressing continues during the grinding operation.
• When predressing starts as shown in Fig. 4.5 (b), the bonding material flows out from
the grinding wheel and an insulating layer composed of the oxidized bonding material is
formed on the wheel surface. Refer Fig. 4.5 (c).
• This insulating layer reduces the conductivity of the wheel surface and prevents
excessive flow out of the bonding material from the wheel. At the same time, the grits
are held by the bonding material and oxide layer.
• The oxide layer is soft and brittle in nature and easily wears off when it comes in contact
with the workpiece during the grinding. Refer Fig. 4.5 (d).
• As grinding continues, diamond grains wear out and cutting force increases. This force
will cause falling off the blunt grits which is held by the brittle insulating material. Refer
Fig. 4.5 (e).
• Due to breakage of insulating layer, electrical conductivity of wheel surface increases
and electrolytic dressing restarts with the flow out of bonding material from grinding
wheel.
• Thus, the profrusions of new diamond grains from the grinding wheel remains constant.

Advantages :
• Good surface finish
• High surface accuracy
• Low subsurface damage

Applications :
• This process is used for grinding of silicon surfaces in semiconductor industry.
• This process produces nano surface finish on glass and ceramics.
• It also helps in production of aspherical surfaces for lenses and moulding dies in optical
industry.
• It is used for precision grinding of bearing steel.
• Finishing of internal cylindrical holes in a hard and brittle material is performed by
ELID.

4.3 Magnetic Abrasive Finishing (MAF)

• We know that, every magnet has two poles [north pole (N) and south pole (S)] and
magnetic lines of force (magnetic field) travels from north pole to south pole.

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• This magnetic principle is used in the Magnetic Abrasive Finishing (MAF) process.
• This process is suitable for finishing of cylindrical workpieces (external and internal
surfaces) and for flat workpieces also.
• It is used for internal finishing of tubes, external finishing of rods, finishing of flat
surfaces, etc.
• The workpiece may be made of ferromagnetic or non - ferromagnetic materials.

Working Principle :
• In MAF process, granular magnetic abrasive composed of ferromagnetic material (as
iron particles) and abrasive grains like Al 2O 3, SiC or diamond dust are used as cutting
tools and the finishing pressure is applied by electro - magnetically generated field.
Refer Fig. 4.6.

Fig. 4.6 : Working principle of MAF

• The magnetic particles are joined to each other magnetically between magnetic poles
along the lines of magnetic force forming Flexible Magnetic Abrasive Brush
(FMAB).
• When a cylindrical workpiece with rotary, vibratory and axial movement is inserted in
such a magnetic field, the finishing of surface and edges is performed by the magnetic
abrasive brush.
• If the workpiece is of non - magnetic material, the lines of magnetic field go around it
(through magnetic abrasives) and if it is of magnetic material then they pass through the
workpiece.
• The magnitude of magnetic force between the two poles is also affected by the material,
shape and size of workpiece as well as magnetic poles.

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• The pressure exerted by the magnetic abrasives is decreased as the gap between the
magnetic pole and workpiece is increased.
• The magnetic abrasives have been used in the form of either a mixture (unbounded) of
abrasive and ferromagnetic particles or abrasive held in a ferromagnetic matrix (bonded)
form by sintering.
• The unbounded magnetic abrasives yield higher metal removal rates whereas bonded
magnetic abrasive give better surface finish.

Process Variables
The process variables of MAF process are as follows :
• Type and size of magnetic abrasives
• Mixing ratio of abrasive grains with ferromagnetic particles
• Working clearance
• Rotational speed and vibration (both amplitude and frequency)
• Material properties of workpiece
• Flux density and relative speed of magnetic abrasive to the workpiece surface.

Advantages :
• MAF process can finish ferromagnetic as well as non - ferromagnetic materials.
• The finishing tool requires neither compensation nor dressing.
• This process has capability to access hard to reach areas.
• The process is capable of modifying roughness without changing the form.
• MAF is able to attain wide range of surface characteristics by careful selection of
magnetic particles.
• The set - up of process is independent of workpiece material. It can easily finish
ceramics, stainless steel, brass, coated carbide and silicon.
• Due to flexible magnetic abrasive brush, it can finish any symmetric workpiece shape.

Disadvantages
• This process is not suitable for mass production.
• It is a time consuming process.
• The cost of process is very high.
• The process is not applicable for some ordinary finishing task where conventional
finishing technique can be easily applied.

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Applications
• MAF is used for finishing of internal surfaces of capillary tubes and other small gauge
needles.
• It is suitable for finishing of cutting tools, airfoils, optics, turbine blades, prosthetics, etc.
• Also suitable for internal finishing of sanitary pipes, food industry, curved pipe, medical
field (stents, catheter shafts, needles, etc.).

4.4 Magneto Rheological Finishing

• Traditional methods of finishing high precision lenses, ceramics and semiconductor
wafers are very expensive and labor intensive.
• Lenses are usually made of brittle materials such as glass, which tends to crack while it
is machined, and every device that uses either lasers or fiber optics requires at least one
high precision lens, increasing its demand higher than ever.
• The lens manufacturer generally uses its in-house opticians for the finishing process,
which makes it an arduous, labor- intensive process.
• Lens manufacturing can be classified into two main processes : grinding and finishing.
• Grinding gets the lens close to the desired size, while finishing removes the cracks
and tiny surfaces imperfections that the grinding process either over looked or created.
• Perhaps the biggest disadvantage to manual grinding and finishing is that it is
nondeterministic
• To overcome these difficulties, Center for Optics Manufacturing (COM) in Rochester,
N.Y. has developed a technology to automate the lens finishing process known as
Magneto Rheological Finishing (MRF).
• The MRF process relies on a unique "smart fluid", known as Magnetorheological (MR)
fluid.
• MR-Fluids are suspensions of micron sized magnetizable particles such as carbonyl
iron, dispersed in a non- magnetic carrier medium like silicone oil, mineral oil or
water.
• In the absence of a magnetic field, an ideal MR-fluid exhibits Newtonian behaviour.
• On the application of an external magnetic field to a MR- suspension, a phenomenon
known as Magneto Rheological Effect, shown in Fig. 4.7 is observed.

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4.4.1 Magneto Rheological Effect

Fig. 4.7 Magnetorheological effect

• Fig. 4.7 (a) shows the random distribution of the particles in the absence of external
magnetic field.
• Fig. 4.7 (c) shows an increasing resistance to an applied shear strain, γ due to this yield
stress.
• When the field is removed, the particles return to their random state and the fluid again
exhibits its original Newtonian behavior.
• In Fig. 4.7 (b) particles magnetize and form columns when external magnetic field is
applied.
• The particles acquire dipole moments proportional to magnetic field strength and when
the dipolar interaction between particles exceeds their thermal energy, the particles
aggregate into chains of dipoles aligned in the field direction.
• Because energy is required to deform and rupture the chains, this micro-structural
transition is responsible for the onset of a large "controllable" finite yield stress.

4.4.2 Magneto Rheological Finishing Process

• In the Magneto rheological finishing process, a convex, flat, or concave work piece is
positioned above a reference surface.
• A MR fluid ribbon is deposited on the rotating wheel rim. By applying magnetic field
in the gap, the stiffened region forms a transient work zone or finishing spot.

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Fig. 4.8 Magnetorheological finsishing process

• Surface smoothing, removal of sub-surface damage, and figure correction are

accomplished by rotating the lens on a spindle at a constant speed while sweeping the
lens about its radius of curvature through the stiffened finishing zone.
• Material removal takes place through the shear stress created as the Magneto
Rheological polishing ribbon is dragged into the converging gap between the part and
carrier surface.
• Deterministic finishing of flats or spheres can be done by mounting the part on rotating
spindle and sweeping it through the spot under computer control, such that dwell time
determines the amount of material removal.
• The zone of contact is restricted to a spot which conforms perfectly to the local
topography of the part.

Fig. 4.9 Vertical MRF machine

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4.4.3 MRP Fluid

• Magneto rheological polishing fluid comprises of MR-fluid with fine abrasive particles
dispersed in it.
• On the application of magnetic field the carbonyl iron particles (CIP) form a chain like
columnar structure with abrasives embedded in between.
• The magnetic force between iron particles encompassing abrasive grain provides
bonding strength to it and its magnitude is a function of iron concentration, applied
magnetic field intensity, magnetic permeability of particles and particle size.
The MR-polishing fluid has following merits:-
1. Its compliance is adjustable through the magnetic field.
2. It carries heat and debris away from the polishing zone.
3. It does not load up as in grinding wheel.
4. It is flexible and adapts the shape of the part of the work piece which is in its contact.

4.4.4 Advantages
• Resistance to applied shear strain by chains is responsible for material removal
• Zone of finishing is restricted to a spot
• Most efficient and for high precision finishing of optics
• MRF makes finishing of free form shapes possible for first time.

Applications
• High precision lenses include medical equipment such as endoscopes
• Military’s night vision equipment like infrared binoculars.

4.5 Magneto Rheological Abrasive Flow Finishing (MRAFF)

• In AFM, the polishing medium acts as compliant lap and overcomes shape limitation
inherent in almost all traditional finishing processes.
• As abrading forces in AFM process mainly depend on rheological behavior of
polymeric medium, which is least controllable by external means, hence lacks
determinism.
• The process magneto rheological finishing, uses magnetically stiffened ribbon to
deterministically finish optical flats, spheres and aspheres.
• In order to maintain the versatility of Abrasive Flow Machining process and at the same
time introducing determinism and controllability of rheological properties of abrasive

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laden medium, a new hybrid process termed as Magnetor heological Abrasive Flow
Finishing (MRAFF) is used.
• This process relies on smart behavior of magneto rheological Fluids whose Rheological
properties are controllable by means of external magnetic field.

Fig. 4.10 Development of magneto rheological abrasive flow finishing process

4.5.1 Mechanism of MRAFF Process

• In MRAFF process, a magnetically stiffened slug of magneto rheological polishing
fluid is extruded back and forth through or across the passage formed by work piece
and fixture.

Fig. 4.11 Mechanism of MRAFF process

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• Abrasion occurs selectively only where the magnetic field is applied across the work
piece surface, keeping the other areas unaffected. The mechanism of the process is
shown in Fig. 4.11.
• The rheological behaviour of polishing fluid changes from nearly Newtonian to
Bingham plastic upon entering and Bingham to Newtonian upon exiting the finishing
zone.

4.5.2 MRAFF Machine

• A hydraulically powered experimental setup is designed to study the process
characteristics and performance.
• The setup consists of two MR-polishing fluid cylinders, two hydraulic actuators,
electromagnet, fixture and supporting frame.
• Experiments were conducted on stainless steel workpieces at different magnetic field
strength to observe its effect on final surface finish.
• No measurable change in surface roughness is observed after finishing at zero magnetic
field.

Fig. 4.12 Schematic of MRAFF machine

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• In MRAFF process, MRPF is extruded through the workpiece passage to be finished

utilizing two opposed cast iron cylinders under the presence of external magnetic field.
• The viscosity of smart magnetorheological polishing fluid (MRPF) is a function of
applied magnetic field strength, and it is varied according to the desire finishing
characteristics.
• The shearing of the Bingham plastic polishing fluid near the workpiece surface
contributes to the material removal and hence finishing.
• Extrusion of the MRP-fluid through the passage formed in the workpiece fixture is
accomplished by driving two opposed pistons in MRPF cylinders using hydraulic
actuators operated in desired manner with the help of designed hydraulic circuit.
• The MRAFF setup consists of MRPF cylinders with pistons, workpiece fixture,
electromagnet, hydraulic drive and controls, and supporting frame.

4.5.3 Advantages
• High machining versatility
• The surface finish improvement by this process is several times better than that of the
original surface finish.
• The cutting activity can be easily controlled
• Process is simple
• Complex structures can be easily machined.
• Localized finishing is possible
• Negligible thermal distortion

Disadvantage
• Machining setup is complex and cost is high.

4.6 Multiple Choice Questions with Answers

MAGNETIC ABRASIVE FINISHING

Q.1 In this type of machining, machining forces are controlled by which of the following
fields?
a Magnetic field b Electric field
c Radiative field d None of the mentioned [Ans. : a]

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Q.2 Which of the following type of tools, are required for magnetic field assisted polishing ?
a Rigid tools b Expensive tools
c Magnetic tools d Ultra precession tools [Ans. : c]

Q.3 Which of the following is not a magnetic field assisted machining process ?
a Electro-plating process b Magnetic abrasive finishing
c Magnetic float polishing d All of the mentioned [Ans. : a]

Q.4 In the advanced machining processes, what is the full form of MAF ?
a Magnet Automated Finishing b Magnetic Abrasive Finishing
c Magnet Assisted Floating d Magnetic Association for Floating [Ans. : b]

Q.5 In magnetic abrasive finishing, which of the following particles do not contribute to the
material removal ?
a Abrasive particles b Magnetic particles
c Non-magnetic particles d All of the mentioned [Ans. : c]

Q.6 Which of the following motions are opted, in order to carry on with the magnetic abrasive
finishing ?
a Rotary motion b Oscillatory motion
c Vibratory motion d All of the mentioned [Ans. : d]

Q.7 Magnetic abrasive finishing is used for which of the following application/s ?
a Surface finishing b Cutting
c Drilling d Boring [Ans. : a]

Q.8 Which is the place, where magnetic field assisted polishing was invented ?
a The United States of America b The United Arab Emirates
c Union of Soviet Socialist Republics d Japan [Ans. : a]

Q.9 Which of the following processes cannot be machined using magnetic abrasive
finishing ?
a Surface finishing b Surface polishing
c Hole Drilling d None of the mentioned [Ans. : c]

Q.10 Which of the following components, come under machining system of magnetic abrasive
finishing ?
a Rotatory spindle b Oscillating Magnets
c Holding chuck d All of the mentioned [Ans. : d]

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Q.11 Which of the following materials can be machined using magnetic abrasive finishing ?
a Alloy steels b Ceramic materials
c Iron materials d All of the mentioned [Ans. : d]

Q.12 State whether the following statement is true or false about magnetic abrasive finishing .
“Vibratory motion that is axial, is introduced in the magnetic field by the oscillation of magnetic
poles.”
a True b False [Ans. : a]

Q.13 Which of the following material/s is/are used to hold the abrasives, in MAF ?
a Nonmagnetic materials b Ferro magnetic materials
c Ceramic materials d None of the mentioned [Ans. : b]

Q.14 What is the other name of ferromagnetic material used for holding the abrasives in MAF?
a Magnetic abrasive conglomerate b Magnetic abrasive holder
c Magnetic abrasive container d Magnetic abrasive ampule [Ans. : a]

Q.15 What are the sizes magnetic abrasive conglomerates required in the machining system
of MAF ?
a 1 - 10 microns b 20 - 50 microns
c 50 - 100 microns d 100 - 200 microns [Ans. : c]

Q.16 What are the size ranges of the abrasives used in magnetic abrasive finishing ?
a 0.1 to 1 microns b 1 to 10 microns
c 10 to 100 microns d 100 to 1000 microns [Ans. : b]

Q.17 Which of the following are commonly used magnetic materials in finishing process ?
a Iron and iron oxides b Nickel and cobalt
c Steel and stainless steel d All of the mentioned [Ans. : d]

Q.18 Which of the following are commonly used abrasive materials in finishing process of
MAF?
a Silicon Carbide b Aluminium Oxide
c Cubic Boron Nitride d All of the mentioned [Ans. : d]

Q.19 Which of the following materials combine to form the magnetic abrasive brush in MAF ?
a Work piece b Magnetic and abrasive particles
c Magnets d All of the mentioned [Ans. : d]

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Q.20 In order to achieve uniform circulation of abrasives, the magnetic abrasives are
undergone through which of the following ?
a Stirring b Oscillation
c Vibration d All of the mentioned [Ans. : a]

Q.21 Magnetic lines of force flows on which part of the work piece material ?
a Through the work piece b Over the surface
c Above the work piece d Below the work piece [Ans. : a]

Q.22 What is the limit of the roller speed used in MAF ?

a Up to 0.5 m/s b Up to 1.3 m/s
c Up to 2.6 m/s d Up to 3.3 m/s [Ans. : b]

Q.23 What is the value of magnetic field intensity used in MAF ?

a 0 - 0.53 Tesla b 0.6 - 0.70 Tesla
c 0.70 - 0.90 Tesla d 0.90 - 1.1 Tesla [Ans. : a]

Q.24 What is the value of magnetic pressure used in Magnetic abrasive machining ?
a 0 - 30 kPa b 50 - 100 kPa
c 100 - 200 kPa d 200 - 500 kPa [Ans. : a]

Q.25 What is the value of frequency used in Magnetic abrasive finishing process ?
a 1 - 10 Hz b 12 - 25 Hz
c 30 - 50 Hz d 60 - 100 Hz [Ans. : b]

Q.26 In which direction, oscillatory motion of magnets are carried out ?

a Axial to work piece b Perpendicular to work piece
c Inclined to work piece d None of the mentioned [Ans. : a]

Q.27 Which of the following surface defects are removed using Magnetic abrasive finishing ?
a Scratches b Hard spots
c Lay lines and tool marks d All of the mentioned [Ans. : d]

Q.28 What is the value of the limited depth to which form errors, tapers, looping can be
corrected ?
a 10 microns b 20 microns
c 30 microns d 40 microns [Ans. : b]

Q.29 State whether the following statement is true or false about magnetic abrasive finishing.
“Increasing the magnetic flux density raises the rate of material removal in finishing.”
a True b False [Ans. : a]

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Q.30 Which of the following factors, does material removal rate depend on ?
a Magnetic flux density b Working clearance
c Work piece material d All of the mentioned [Ans. : d]

Q.31 Which of the following factors does not affect the magnetic abrasive conglomerates in
MAF ?
a Abrasive type b Abrasive size
c Work piece material d Volume fraction [Ans. : c]

Q.32 State whether the following statement is true or false about magnetic abrasive finishing.
“Higher rates of material removal are obtained, with an increase in amplitude and frequency.”
a True b False [Ans. : a]

Q.33 Which of the following applications where MAF is used ?

a Finishing of inner surfaces b Polishing of balls and rollers
c Chamfering and deburring of gears d All of the mentioned [Ans. : d]

Q.34 Diamond abrasives used for finishing operation results in which type of surface
defects ?
a Deep pits b Surface scratches
c Micro cracks d All of the mentioned [Ans. : d]

Q.35 Which of the following conditions is/are not suitable for finishing of ceramic balls ?
a Controlled force b Large abrasive sizes
c Small abrasive sizes d Less harder abrasives [Ans. : b]

Q.36 In MAF, ceramic balls and the bearing rollers are placed in between which components ?
a Abrasives and float b Drive shaft and float
c Float and magnets d Magnets and abrasives [Ans. : b]

Q.37 Polishing in magnetic abrasive finishing is done, by which action of material removal?
a Mechanical abrasion b Mechanical erosion
c Chemical corrosion d Material vaporization [Ans. : a]

Q.38 State whether the following statement is true or false regarding MAF.
“As the forces exerted on the rollers are very small, polishing actions takes place very finely.”
a True b False [Ans. : a]
Q.39 For obtaining a better finish using magnetic abrasive finishing, tubes are rotated at
which speeds ?
a Very low b Low c Medium d Very High [Ans. : d]

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Q.40 Which of the following is an advantage of MAF over electrolytic finishing ?

a Disposing of electrolyte b Cost effective
c More flexible d More accuracy [Ans. : a]

Q.41 State whether the following statement is true or false about magnetic abrasive finishing.
“Mirror finishing, removed burrs with lowering the accuracy of the shape are achieved by
MAF.”
a True b False [Ans. : b]

Q.42 What are the other applications where magnetic abrasive finishing can be used ?
a Removal of oxide layers b Removal of protective coatings
c Chamfering d All of the mentioned [Ans. : d]

Q.43 Chemical micromachining is used for engraving the metal.

a True b False [Ans. : a]

Q.44 It is required to remove material in the form of atoms for finishing of the surface.
a True b False [Ans. : a]

[viscoelastic material, carbonyl iron particles, or by the magnetorheological fluid as a carrier]

Q.45 Magneto Rheological Abrasive Finishing (MRF) is a magnetic field assisted process.
a True b False [Ans. : a]

Q.46 MRF is used for finishing of brittle materials.

a True b False [Ans. : a]

Q.47 Abrasive Flow Machining (AFM) is used for .

a de-burring b etching
c drilling d cutting [Ans. : a]

Q.48 In Chemo-Mechanical Polishing (CMP) process, material is removed due to abrading.

a True b False [Ans. : a]

Q.49 CMP is used for flat surfaces only.

a True b False [Ans. : a]

Q.50 MAF was developed to produce efficiently and economically good quality finish material.
a True b False [Ans. : a]

Q.51 Magnetic float polishing is a technique based on .

a magneto-dynamic behaviour b magneto-hydrodynamic behaviour
c kinematic behaviour d viscosity [Ans. : b]

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Q.52 Ferromagnetic particles are attracted towards the area of a higher magnetic field.
a True b False [Ans. : a]

Q.53 MRAFF is the hybrid finishing process of MRF and AFF.

a True b False [Ans. : a]

Q.54 In magnetic flow polishing process, very small force is applied by the abrasives.
a True b False [Ans. : a]

Q.55 For replication of micro parts moulding is preferred .

a True b False [Ans. : a]

Q.56 Magnetorheological fluids are

a viscous dominant fluids b elastic dominant fluids
c viscoelastic fluids d none of these [Ans. : d]

Q.57 The force that is responsible for shearing of surface peaks in magnetorheological
finishing is
a normal force generated between workpiece and rotating wheel
b tangential force at the surface of abrasive particle and surface peak interaction
c vector sum of both normal force and tangential force
d no mechanical forces are generated in magnetorheological finishing process. [Ans. : b]

Q.58 Passivation layer in chemical mechanical polishing process indicates

a Chemically reacted layer of surface b Conversion layer due to heat interaction
c Contaminated layer due to polishing slurry d Mechanically destroyed layer [Ans. : a]

Q.59 The full form of CMP process

a Chemomechanical Polishing b Chemomechanical Planarization
c Chemomechanical Presipiration d Both a and b [Ans. : d]

Q.60 Which of the following is not an advantage of magnetorheological finishing process?

a Used to finish lenses in optical industry
b Blind holes can be finished
c Polishing and deburring options can be combined
d Finishing rates are higher than manual finishing [Ans. : b]

Q.61 Magnetorheological abrasive flow finishing process adopts the advantages of .

a Complex component finishing capability
b Controlling viscosity of the media with external means from AFF process
c Both a & b d None of these [Ans. : d]

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Q.62 Rheology is a science of

a fluid dynamics b flow and deformation of fluids
c deformation of solids d fluid behaviour under extrusion pressure
[Ans. : b]

Q.63 Which one of the following is not an important level element of the AFF process ?
a Medium b Tooling
c Volume of hydraulic oil d Machine setup [Ans. : c]

Q.64 A strong flexible magnetic abrasive brush is seen in finishing of .

a Ferro magnetic materials b Non – ferro magnetic material

c Not depends on type of material d Para magnetic materials [Ans. : a]

Q.65 Which one of the following statement is correct with respect too abrasive flow
machining ?
a Axial force is responsible for indentations
b Radial force is responsible for shearing of roughness peaks
c The velocity in the radial direction of media is higher than the axial velocity
d None of these [Ans. : d]

Advanced Nano Finishing Processes ends …

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Notes

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 Phase Diagrams

Syllabus : Recent developments in non-traditional machining processes, their working

principles, equipments, effect of process parameters, applications, advantages and
limitations. Comparison of non-traditional machining processes.

Section No. Topic Name Page No.

5.1 Electro Chemical Deburring (ECD) 5-2

5.2 Electrolyte Jet Machining (EJM) 5-5

5.3 Laser Surface Treatments 5-7

5.4 Comparison of Advanced Machining Processes 5-8

5.5 Recent Developments in EDM 5-9

5.6 Recent Developments in Wire Cut EDM 5 - 11

5.7 Multiple Choice Questions with Answers 5 - 12

 Recent Trends in Non-Traditional Machining Processes

5.1 Electro Chemical Deburring (ECD)

 When the component is processed by a conventional machining method, it is left with
burrs, specifically along the two intersecting surfaces.
 Such burrs are undesirable from the viewpoint of performance of a component as well as
safety of an operator or other person.
 Such burrs can be removed by one of the deburring processes.
 The problems of burrs are still persisting and unsolved in many industries. Different
attempts are made to reduce the burr level by various means.
 Deburring is an important phase for manufacturing quality products, mainly in large
scale industries.
 In a modern industrial technology, the deburring process has attained great importance
because of rigid quality standards. However, the cost of deburring should not be very
high.
 The deburring process can be classified as follows :
i) Mechanical deburring : It is performed by using cutting tools, brushes, belt sanders,
etc.
ii) Abrasive deburring : In this technique tumbling, barrel finishing, vibratory
deburring, sand blasting, etc. methods are used.
iii) Thermal deburring : In this technique, the components are placed in the chamber
which is filled with combustible gas mixture of oxygen and hydrogen. After ignition
by spark plug, the heat wave is generated and burrs or sharp edges are removed.
iv) Electrochemical deburring :
 This process makes use of flowing electrolyte for conducting electric current for the
electrochemical reaction to take place.
 The current rating and current duration for a particular component are found after
extensive trials for each type of component.
 The commonly used electrolytes are sodium chloride (NaCl) and sodium nitrate
(NaNO3).
 Due to corrosive nature of electrolyte and ferrous hydroxide released by the process,
the machines are built with non - corrosive materials.
 This technique is generally used for far away located and inaccessible places where
other deburring processes are not effective.

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 Recent Trends in Non-Traditional Machining Processes

Working Principle of ECD

 It consists of the following elements or sections :
o Electrolyte system (to provide high velocity to the flow)
o Electrical power system (to supply current)
o Mechanical structure (to locate and provide movement or mounting of the electrodes)
o Separator (to separate the sludge)
 During the process when a voltage is applied between two metal electrodes immersed in
an electrolyte, current flows through the electrolyte from one electrode to another
electrode. Also, ions (electrically charged atoms) physically migrate through the
electrolyte. Refer Fig. 5.1.

Fig. 5.1 Electromechanical deburring

 The transfer of electrons between the ions and electrodes completes the circuit and
brings the phenomenon of metal dissolution at the positive electrode or anode
(workpiece).
 Metal detached atom by atom from the anode surface appears in the main body of the
electrolyte as positive ions or as precipitated semi - solid of the metal hydroxide. The
dissolved burrs in the form of hydroxides settle down and the electrolyte is regenerated.
 Generally, the tool is insulated on all surfaces, except a part of which is adjacent to the
burr or burrs.
 But, the setting of dimensions of the bare part of the tool, machining time and other
conditions are decided by trial and error method.
 The electrolyte is made to flow through the inter-electrode gap which is generally 0.1 to
0.3 mm.

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 Recent Trends in Non-Traditional Machining Processes

 The electrolyte is properly filtered out before its recirculation and the hydroxide is
disposed through outlet drain.
 The hydroxide removed from the drain valve is extensively used as a raw material for
lapping paste.
 Before deburring, the components should be free from loose burrs which damage the
electrodes, and also from grease/ oil which contaminates the electrolyte.
 Hence, workpiece should be thoroughly washed out before deburring. After deburring, it
should be immediately dipped in running water followed by dewatering fluid which
protects against the corrosion.

Advantages
 During the process there are no mechanical loads or thermal loads on the workpiece.
 Both workpiece roughing and finishing can be completed in a single pass. Because ECD
is a dissolution process, no primary or secondary burrs are generated.
 ECD is a highly productive process. The process time is fast as compared to
conventional methods and multiple parts per cycle can be machined. This results in low
unit cost of production.
 It is a highly stable process with good process control which ensures accuracy, quality,
consistency and the highest repeatability.
 It is an ideal deburring process for parts where burns are difficult to reach or machine
using conventional methods. It also eliminates the problem of secondary burr formation.

Disadvantages
 The acidic electrolyte can corrode the tool, workpiece or equipments.
 Only electrically conductive materials can be machined.
 High specific energy consumption.

Applications
 ECD has applications in industries like consumer appliances, biomedical, aerospace,
automobile, etc.
 It is used for the components like gears, splines, drilled holes, milled parts, fuel supply
and hydraulic system components, etc.
 Also used in cases where two holes cross each other like crank shaft.

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 Recent Trends in Non-Traditional Machining Processes

5.2 Electrolyte Jet Machining (EJM)

 EJM is an advance version of Electrochemical Machining (ECM).
 In EJM a workpiece is machined only in the area hit by the electrolyte jet which is
ejected from a nozzle.
 By translating the jet over the workpiece, intricate patterns can be fabricated without
using the special mask.
 Even 3D shapes can be machined by adjusting the current and dwelling time of the jet
over the workpiece.
 As EJM is an electrochemical process, there are no burns, cracks or heat affected zones
generated by the process.
 This process is used for removing processes by anodic dissolution as well as for coloring
processes by anodic oxidation.
 Both glossy surface and considerably rough surface can be obtained by controlling the
current density.

Working Principle :
 It is carried out by jetting electrolytic aqueous solution from the nozzle towards the
workpiece while applying voltage to the gap as shown in Fig. 5.2.
 Fig. 5.2 shows the electric potential distribution in the electrolyte flow ejected from a
cylindrical nozzle and current density distribution over the workpiece surface.
 When the electrolyte jet hits the workpiece at high flow rate, the electrolyte flows
rapidly outward in a fast thin layer. This suddenly changes its thickness in area far away
from the nozzle due to hydraulic jump phenomenon.

Fig. 5.2 : Working principle of EJM

 A platinum wire is inserted in a glass tube nozzle. When electrolyte pass through this, it
acts as cathode and workpiece acts as anode. By electrolytic dissolution metal removal

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takes place. Metal ions are carried out by flow of electrolyte.

 Fig. 5.3 shows the set - up of EJM. The workpiece is mounted on a table which is placed
in a work sink to drain the electrolyte.
 The work sink and nozzle are installed on a platform which can be numerically
controlled.
 The electrolyte is supplied from a gear pump whose flow rate can be controlled by
varying the pump speed.

Fig. 5.3 Set - up of EJM

Advantages :
 There are no heat affected zones in the process.
 No residual stresses in the component.
 Tool wear is minimum.
 Additional masking is not required.
 Good surface finish can be obtained.
 It is a non - contact type machining process.

Applications :
Applications of electrolytic jet machining :
 This process is used for drilling small holes in aircraft turbine blades.
 It is used for producing maskless patterns for microelectronics parts.
 It is used to machine hard alloys.
 This process is used to make surface glossy.
 It has large applications in biomedical field as well as in Micro Fluidic systems.

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5.3 Laser Surface Treatments

Laser based heat treatment

 Heating the steel upto it's melting point and then quickly quenching it leads to
hardening.
 In laser based heat treatment, surface layer of workpiece is heated upto a temperature to
form austenite.
 Specimen is moved away from laser at constant feed rate. At the moment it moves down
from exposure to the laser it is quenched by cooler region rapidly.

Fig. 5.4

 As the temperature drops rapidly, austenite becomes mechanically unstable and

rearrange to form a body centered crystal structure which is harder than the original
material.
 The factors affecting this are, nature of metal coating, wavelength and shape of laser
beam.
 The lasers used in laser based heat treatment can be gas lasers or state lasers.
 Carbon dioxide lasers are used in this process but their absorption by metals is difficult.
 Yttrium Aluminium Garnet lasers used in the process have high absorption properties
but less electrical efficiency.
 High power diode lasers are used, which are most significant. They have higher
efficiency as well as better absorption properties.

5.3.1 Factors Affecting the Performance of Laser based Heat Treatment

 Factors which affect the performance of laser-based heat treatment are :
i) Power Density : Higher the power density, deeper is the case depth. However, if all
the variables are fixed a maximum depth can be achieved.

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ii) Travel Speed : If the travel speed is increased, case depth will be decreased until
there is no reaction with the material. Decreased travel speed will result into
significant surface melting or a lower hardness.
iii) Requirement of Hardness : When a maximum hardness is required for a certain
carbon content, then the case depth is controlled by the cooling condition of the part.
If the hardness requirement is lower, then we can lower the power density and reduce
the travel speed.
iv) Cooling Condition : At least six or seven times the case depth thickness of material
is needed beneath the surface to insure reaching the required case depth and hardness.
Air jets, water mist or oil can be untilized for this purpose.

5.4 Comparison of Advanced Machining Processes

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5.5 Recent Developments in EDM

1. Adaptive control
The purpose of the adaptive control in an EDM is to read the conditions of the EDM spark
and translate these conditions into digital signals that are fed into the machine’s controller. The
controller translates these signals, determines the efficiency of the EDM cut and makes
adjustments accordingly. One of the conditions monitored by the machine’s adaptive control
technology is contamination in the gap. If excess contamination in the gap is present, this
creates the potential for an EDM arc or diminished performance. The controller must then
make adjustments that do not affect the over burn or surface integrity of the workpiece. This
generally involves changes in the gap voltage, increasing the off-time, altering the jump cycle
or a combination of any of these.

2. Research progress in vibration rotary and Vibro-Rotary EDM

It was proved that the electrode rotation served as an effective gap flushing technique,
yielding better material removal. combination of ultrasonic vibration in EDM the MRR and
surface finish improved and TWR increased. Vibration, rotary and vibro-rotary mechanism
makes the equipment simple and increases the material removal rate, provide better surface

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finish ejection from work piece. Better circulation of dielectric fluid and debris removal from
work piece.

3. Water In EDM
Water as dielectric is an alternative to hydro carbon oil. The approach is taken to promote a
better health and safe environment while working with EDM. This is because hydrocarbon oil
such as kerosene will decompose and release harmful vapour (CO and CH4). Water-based
dielectric can replace hydrocarbon oils since it is environmentally safe. Water based EDM is
more eco friendly, reduced harmful agent, toxic fumes dangerous for human & economically
low cost machining as compared to conventional oil based dielectric. The material removal
rate enhanced with use of water.

4. Dry EDM
Dry EDM is a green environment friendly Electric discharge machining Technique in
which the liquid dielectric is replaced by a gaseous dielectric. Gas at high pressure as used as
the dielectric medium. Dry EDM is eco-friendly machining. Pollution is reduced by use of gas
instead of oil based dielectric. Harmful & toxic fumes are not generated during machining.
Material removal rate &electrode wear ratio also get enhanced by dry EDM.

5. Powder Mixed EDM

Powder mixed electric discharge machining (PMEDM) is one of the new innovations for
the enhancement of capabilities of electric discharge machining process. In this process, a
suitable material in fine powder is properly mixed into the dielectric fluid. The added powder
improves the breakdown characteristics of the dielectric fluid.

Fig. 5.5

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5.6 Recent Developments in Wire Cut EDM

1. Wire EDM with Coated Electrodes

Wire electrodes coated with low vaporization temperature metal or alloy gives more
protection to the core of the wire from thermal shock. high performance coated wires, having
high conductivity and better flushability have been developed and used for machining,
resulting in better surface finish and improved cutting speeds. But these wire are costly as well
as cause many impurities in dielectric fluid and also some environmental hazards.

2. Wire EDM With Multi- Layered Electrodes

A wire electrode, which includes a steel core coated with copper or some other materials.
Large amount of work has been reported in various patents for multi layered steel core wire
electrodes and majority of these multi layered wire electrodes results in accuracy and precision
problems with increased tool life. It may be therefore concluded that coating is done on the
steel wires to achieve high strength and rigidity.

3. Wire EDM with Advance Power Supply

The supply is transistor controlled and composed of a full bridge circuit, two snubber
circuits and a pulse control circuit, to provide the functions of anti-electrolysis, high frequency
and very low energy pulse control.

4. New Control System to Improve Machining Accuracy

A closed loop wire tension control system for WEDM to improve the machining accuracy.
Dynamic performance of the closed loop wire tension system was examined by Proportional
Integrate (P.I.) controller and one step ahead controller. Further in order to reduce the vibration
of the wire electrode, dynamic dampers were employed.

5. Wire Electrodes with Cryogenic Treatment

In electronics industries, Aluminum, Brass, Copper, Tin, Lead shows better wear resistance
after cryogenic treatment. EN 31 steel, when machined with cryogenic treated brass wire, with
three process parameters namely type of wire electrode, pulse width, and wire tension, shows a
significant improvement in Surface Roughness than the untreated wire electrode.

6. Stratified wires
Properties of the wire used in this process have an impact on MRR and quality of the cut
surface. Now a days stratified wires are used as electrodes. These wires are made of copper
core within a thin layer of zinc over it. Such a current carry more current hence gives high
MRR. This wire is used only once and then scrapped because it is not very expensive. A wire

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can carry heavier load if it can absorb more amount of heat without breaking. A heavier load
also means a spark with more energy hence higher MRR resulting in higher cutting speed.
Zinc melts and even evaporates at a temperature lower than the melting temperature of copper.

Fig. 5.6 Stratified wire used in wire EDM

5.7 Multiple Choice Questions with Answers

ICE JET MACHINING

Q.1 In the existing advanced machining processes, what is the full form of IJM ?
a Ice jet manufacturing b Ink jet manufacturing
c Ice jet machining d Ink jet machining [Ans. : c]

Q.2 In ice jet machining, the abrasive particles used for material removal are replaced by
which of the following ?
a Silica particles b Ice particles
c Fluids d Colloidal solutions [Ans. : b]

Q.3 When compared to abrasive water jet machining, how are the material removal rates in
Ice jet machining ?
a Very low b Low
c High d Remains same [Ans. : b]

Q.4 State whether the following statement is true or false about ice jet machining.
“Water can be reused in IJM, unlike that of AWJM and WJM.”
a True b False [Ans. : a]

Q.5 Which of the following are the components of machining system of IJM ?
a High pressure pump b Ice particle generator
c Ultrasonic atomizer d All of the mentioned [Ans. : d]

Q.6 Which of the following component will be present just after the cooling coil ?
a High pressure pump b Ice particle generator
c Cutting nozzle d Ultrasonic atomizer [Ans. : c]

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Q.7 Ice particles of size <500 μm are produced by which of the following process ?
a Stream freezing b Ice particles supply
c Normal cooling d None of the mentioned [Ans. : a]

Q.8 Ice particles of size >500 μm are produced by which of the following process ?
a Stream freezing b Ice particles supply
c Normal cooling d None of the mentioned [Ans. : b]

Q.9 In ice jet machining, stand-off distance value varies between which of the following ?
a 1.0 – 2.0 mm b 2.0 – 3.0 mm
c 3.0 – 5.0 mm d 5.0 – 10.0 mm [Ans. : c]

Q.10 What is the value of diameter of nozzle that is used in ice jet machining ?
a 0.175 mm b 0.425 mm
c 0.548 mm d 0.654 mm [Ans. : a]

Explanation : The value of diameter of nozzle in Ice jet machining is about 0.175 mm.

Q.11 Ultrasonic atomizer used in ice particle generator, produces water droplets at which
rate ?
a 0.1 ltr/hr to 1 ltr/hr b 2 ltr/hr to 12 ltr/hr
c 20 ltr/hr to 35 ltr/hr d 40 ltr/hr to 65 ltr/hr [Ans. : b]

Q.12 What are the advantages of ice jet machining over the other advanced machining
processes ?
a Environmentally safe b Cost reduction
c No heat affected zone d All of the mentioned [Ans. : d]

Q.13 Which of the following is a disadvantage of ice jet machining when compared to AWJM ?
a Environmentally safe b Cost reduction
c Low material removal rate d No heat affected zone [Ans. : c]

Q.14 Which of the following are the processes and applications by the use of IJM ?
a Ice deburring process b Ice cutting process
c Ice blasting process d All of the mentioned [Ans. : d]

Q.15 Which of the following industries use Ice jet machining for different applications ?
a Food industry b Medical industry
c Space industry d All of the mentioned [Ans. : d]

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PHOTO CHEMICAL MILLING

Q.16 In advanced machining process, what is the full form of PCM ?
a Photochemical manufacturing b Photochemical machining
c Photo crystalline manufacturing d Photo crystalline machining [Ans. : b]

Q.17 In this method, which of the following techniques are used to apply the maskant on the
machining surface ?
a Photographic techniques b Cut and peel masking
c Silkscreen resist technique d None of the mentioned [Ans. : a]

Q.18 What is the similarity between normal chemical milling process and photo chemical
milling ?
a Both use chemicals b Maskant application method
c None of the mentioned d All of the mentioned [Ans. : a]

Q.19 In some cases, photochemical milling can also be called as .

a photo chemical blasting b photo chemical blanking
c photo chemical drilling d photo chemical erosion [Ans. : b]

Q.20 Photo chemical blanking can be used to machine the parts to high precision, up to which
of the following thickness values ?
a 0.001 – 0.007 mm b 0.007 – 0.012 mm
c 0.013 – 1.503 mm d 1.612 – 2.125 mm [Ans. : c]

Q.21 State whether the following statement is true or false regarding photochemical milling.
“Unlike that of CHM, PCM can also be used to create parts.”
a True b False [Ans. : a]

Q.22 In case of photochemical milling that use using lettering and graphics for surface
etching, what will be the depth of surface etched ?
a Very deep b Up to certain depth
c Half-way d None of the mentioned [Ans. : b]

Q.23 When was the process, photochemical milling is introduced to the machining
environment ?
a 1920s b 1930s
c 1950s d 1960s [Ans. : d]

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Q.24 State whether the following statement is true or false regarding PCM.
“In PCM, etching depth does not depend on the time, a component is immersed in the
chemical solution.”
a True b False [Ans. : b]

Explanation : As in case of CHM, depth of etch in PCM depend upon the time of part immersed in

chemical solution.

Q.25 Which of the following processes does not come under chemical machining processes ?
a Chemical milling b Photo forming
c Photo chemical filling d Photo chemical blanking [Ans. : b]

ELECTROSTREAM DRILLING

Q.26 In advanced machining processes, what is the full form of ES drilling ?

a Electro stream b Electrical shaped
c Electron shaped d Electric shock [Ans. : a]

Q.27 This electrostream drilling is used when we cannot drill which of the following type of
holes ?
a Too deep holes by EDM b Small holes by STEM
c All of the mentioned d None of the mentioned [Ans. : c]

Q.28 What is the value of diameter of glass nozzle used in electrostream drilling ?
a 0.01 - 0.02 mm b 0.025 - 0.5 mm
c 0.5 - 0.75 mm d 0.75 - 1.25 mm [Ans. : b]

Q.29 Compared to the required diameter of the hole, how is the nozzle diameter ?
a Smaller b Larger
c Same as required d All of the mentioned [Ans. : a]

Q.30 Which of the following acts as the cathodic tool in ES drilling ?

a Titanium base b Platinum wire
c Glass nozzle d Work piece [Ans. : b]

Q.31 What is the concentration of electrolytes that are commonly used in ES drilling ?
a 1 to 10 wt % b 12 to 20 wt %
c 23 to 30 wt % d 34 to 50 wt % [Ans. : b]

Q.32 State whether the following statement is true or false regarding ES drilling.
“In ES drilling, hydrochloric acid is used for machining aluminium and its alloys.”
a True b False [Ans. : a]

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Q.33 Which of the following are the metals, which can be machined using sulphuric acid ?
a Carbon steels b Haste alloy
c Inconel d All of the mentioned [Ans. : d]

Q.34 What are the values of electrolyte pressure recommended for ES drilling ?
a 50 - 100 kPa b 100 - 250 kPa
c 275 - 400 kPa d 500 - 750 kPa [Ans. : c]

Q.35 Which of the following parameters must be carefully monitored for satisfactory
machining ?
a Acid temperature b Pressure
c Concentration d All of the mentioned [Ans. : d]

Q.36 What are the values of voltages used in ES drilling process ?

a 10 to 40 V b 40 to 70 V
c 70 to 150 V d 150 to 300 V [Ans. : c]

Q.37 What are the values of feed rates used in ES drilling process ?
a 0.01 to 0.5 mm/min b 0.75 to 2.5 mm/min
c 3 to 4.5 mm/min d 5 to 7.5 mm/min [Ans. : b]

Q.38 Higher material removal rates are associated with feed rates and
tool diameters.
a larger, smaller b smaller, larger
c smaller, smaller d larger, larger [Ans. : d]

Q.39 What are the normal hole depth tolerance values in ES drilling ?
a ± 0.03 mm b ± 0.05 mm
c ± 0.07 mm d ± 0.09 mm [Ans. : b]

Q.40 How many holes can be drilled simultaneously using ES drilling process ?
a One hole b Two holes
c Three holes d Multiple holes [Ans. : d]

Q.41 What is the full form of IBM in the advanced machining processes ?
a Ion beam machining b Ion beam manufacturing
c Ion blast machining d Ion blast manufacturing [Ans. : a]

Q.42 State whether the following statement is true or false regarding IBM.
“In IBM, vacuum chamber is not necessary unlike that of Electron beam machining.”
a True b False [Ans. : b]

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Q.43 Which of the following are the components of Ion beam machining ?
a Vacuum chamber b Voltage source
c Tungsten filament cathode d All of the mentioned [Ans. : d]

Q.44 How does the ions strike the work piece in machining using IBM ?
a Oblique striking b Normal incident striking
c Oblique & Normal incident striking d None of the mentioned [Ans. : c]

Q.45 Number of atoms yielded in oblique cutting is normal incidence.

a greater than b lesser than
c same as d none of the mentioned [Ans. : a]

Q.46 How much amount of energy is required for effective removal of atoms ?
a 1 to 5 eV b 5 to 10 eV
c 10 to 15 eV d 15 to 20 eV [Ans. : b]

Q.47 Machining rates in IBM depend on which of the following factors ?

a Work piece material b Ions type
c Incident angle d All of the mentioned [Ans. : d]

Q.48 What is the value of voltage required for machining in Ion beam machining ?
a 1 kV b 2 kV
c 3 kV d 4 kV [Ans. : a]

Q.49 What are the values of current densities required in IBM ?

a 0.25 mA/cm2 b 0.35 mA/cm2
c 0.55 mA/cm2 d 0.85 mA/cm2 [Ans. : d]

Q.50 What is the value of beam diameter that is obtained in IBM ?

a 1 cm b 3 cm
c 5 cm d 7 cm [Ans. : c]

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