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Seminar report Himanshu

Computer Science and Engineering (MBM Engineering College)

Studocu is not sponsored or endorsed by any college or university

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APPLICATION OF CUTTING FLUIDS IN

MACHINING OF TITANIUM ALLOYS

A Seminar Report

Submitted by

HIMANSHU
in partial fulfillment for the award of the degree
of
BACHELOR OF TECHNOLOGY
IN

MECHANICAL ENGINEERING

At

JIET GROUP OF INSTITUTIONS

JODHPUR INSTITUTE OF ENGINEERING AND
TECHNOLOGY
NH-62, NEW PALI ROAD, MOGRA
JODHPUR

SESSION 2019-20

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CERTIFICATE

This is to certify that seminar titled <APPLICATION OF CUTTING

FLUIDS IN MACHINING OF TITANIUM ALLOYS= being
submitted by HIMANSHU of B.Tech. final year, Roll
No.16EJIME033 in partial fulfillment for the award of degree of
Bachelor of Technology in Mechanical Engineering, at JIET,
Jodhpur affiliated with RTU, Kota as a record of student’s own
work carried out by him under guidance of the undersigned.
He has not submitted the matter embodied in the seminar in this
form for the award of any other degree.

Prof. (Dr.) Deepak Mehra Prof. (Dr.) Deepak Mehra

Professor & Head, Professor & Head,
Dept. of Mech. Engg. Dept. of Mech. Engg.

External Examiner_________________________

Internal Examiner__________________________
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ACKNOWLEDGMENT

It gives me a great sense of pleasure to present the report of the B.Tech Seminar
undertaken during B.Tech. Final Year. I owe special debt of gratitude to Prof. (Dr.)
Deepak Mehra (Head of Department) Mechanical Engineering), who gave me this
great opportunity to increase my technical knowledge with providing all the required
resources for the successful completion my seminar.

Also as Guide, for his constant support and guidance throughout the course of our
work. His sincerity, thoroughness and perseverance have been a constant source of
inspiration for me. It is only his cognizant efforts that our endeavors have seen light
of the day.

I would like to thank our seminar coordinator Er. Mohd Jawed Iqbal for providing
me the critical views on the seminar topic.

I also do not like to miss the opportunity to acknowledge the contribution of all
faculty members of the department for their kind assistance and cooperation during
the development of our seminar. Last but not the least, I acknowledge my friends for
their contribution in the completion of the seminar.

HIMANSHU
16EJIME033
B.tech. Final year
Mechanical Dept.

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TABLE OF CONTENTS
CHAPTER NO. TITLE PAGE NO.
ACKNOWLEDGEMENT 3
ABSTRACT 7
1. INTRODUCTION 8
1.1. TITANIUM ALLOYS 9
1.2. TITANIUM BREAKTHROUGH 10
1.3. MACHINING OF TITANIUM 10
2. LITERATURE REVIEW 13
2.1 CURRENT STATUS OF RESEARCH 13
2.2 INFERENCES DRAWN FROM LITERATURE 14
REVIEW
3. SOLUTIONS TO OVERCOME 16
MACHINING DIFFICULTIES
3.1 DRY MACHINING 17
3.2 CUTTING FLUIDS 17
3.3 FLOOD LUBRICATION 18
3.4 MINIMUM QUALITY LUBRICATION 24
3.5 CRYOGENIC COOLING 26
4. APPLICATION & FUTURE SCOPE 28
4.1 APPLICATION 28
4.1.1 TITANIUM THE <AEROSPACE METAL= 28
4.1.2 OCEAN ENGINEERING 29
4.1.3 MEDICAL DEVELOPMENT 29
4.1.4 AUTOMOTIVE 29
4.1.5 CHEMICAL 30
4.2 FUTURE SCOPE 30
5. CONCLUSIONS 31
REFERENCES 33
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LIST OF FIGURES:
Serial Number Title Page No.
1 Classification of machining processes for titanium 16
alloys
2 Tabular data for different titanium alloys studied by 16
researchers
3 Direction of application of cutting fluids 17
4 Titanium cuttings (a) dry cutting, (b) flood lubrication, 19
(c) 60 bar through tool
5 Tool Life data for Ti-10V-2Fe-3Al turned with flood 19
lubrication
6 Schematic drawing of the coolant system 20
7 Tool wear under different coolant: (a) Conventional 21
coolant; (b) Graphene oxide suspended fluid
8 SEM images of hole surface machined with 21
conventional coolant: (a) Hole surface 150x; (b) Hole
surface 500x
9 SEM image of chip formation under two different 22
coolant: (a) Conventional coolant; (b) Graphene oxide
suspended fluid
10 ACF spray system in milling setup 23
11 Chip morphology when machining 23
12 Chip analysis under MQCF and RFVT-MQCF 25
conditions at Cutting speed: 275
m/min, feed rate: 0.13 mm/rev & depth of cut: 0.5 mm
under RHVT-MQCF conditions
13 Tool wear at different lubrications 26
14 Summary of research on cryogenic cooling of titanium 27
alloy
15 Percentage of titanium in Boeing 787 28
16 Titanium Knee joint 29

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LIST OF TABLES

Serial Number Title Page No.

1 V15 surface speed for two alloys with three coolant 20
conditions

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ABSTRACT

Titanium alloys are metals that contain a mixture of titanium and other chemical elements.

Such alloys have very high tensile strength and toughness (even at extreme temperatures).

They are light in weight, have extraordinary corrosion resistance and the ability to

withstand extreme temperatures. There are 4 varieties of titanium alloys. Titanium alloys

typically contain traces of aluminium, molybdenum, vanadium, niobium, tantalum,

zirconium, manganese, iron, chromium, cobalt, nickel, and copper. The four grades, or

varieties of titanium alloys are Ti 6AL-4V, Ti 6AL ELI, Ti 3Al 2.5 and Ti 5Al-2.5Sn.

Titanium alloys are light weight, possess high strength, have excellent fatigue performance

and offer high resistance to an aggressive environment therefore are used in many fields

such as aerospace, biomedical, energy industries. Machining of titanium is a challenging

task due to their high strength, low thermal conductivity and chemical reactivity with tool

materials (at elevated temperatures), pose a hazard to the tool and significantly reduce the

tool life. In addition, a relatively low Young’s modulus of titanium alloys leads to spring-

back and chatter leading to poor surface quality of the finished product, during turning and

drilling, long continuous chips are produced; causing their entanglement with the cutting

tool and making automated machining near impossible. In order to achieve sustainable

machining different strategies for application of cutting fluids are developed such as

through-tool delivery of emission coolant flood lubrication, minimum quantity lubrication

(MQL), minimum quantity cooled lubrication (MQCL), cryogenic cooling, Atomization

based cutting fluid spray system.

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CHAPTER 1

INTRODUCTION

With the advancements in material science, newer materials with enhanced properties are being
produced. Based on the requirements, alloys with properties like high strength and hardness are
replacing the conventional metals and alloys in various engineering applications. While such
materials are functionally useful, they pose problems during machining.

Increased strength and hardness of the materials generate high temperatures during machining and
accelerate tool wear [1]. Such materials are known as <difficult-to-machine= materials. Titanium
and nickel alloys are the most popularly used difficult to machine engineering materials.

Titanium alloys are extensively used in the aerospace, structural, biomedical, and defence
applications due to their superior properties like high fatigue strength, high yield strength, and high
strength to weight ratio, resistance to high temperatures, biocompatibility, and high corrosion
resistance [2]. Though pure titanium is a soft metal, its alloys have superior properties comparable
to nickel alloys. Still, the density of the alloys is low, almost similar to aluminium. This makes the
alloys useful for aerospace applications.

Titanium has played a major part in the history of the world from the mid-20th century up until
today. It was discovered in the 1700s, produced in small quantities until the late 1800s, and finally
went into commercial production once the Kroll process was devised and the militaries of different
countries started to understand its importance.

Titanium was first discovered in 1791 by an English pastor named William Gregor. The Reverend
was analysing some black magnetic sand from Cornwall when he came across a residue he couldn’t
identify. He believed it was a new metal, and that was confirmed a couple years later (1793) by the
German chemist M.H. Klaproth. When Dr. Klaproth identified the oxide, he also named it titanium,
after the Titans of Greek mythology.

Despite the discovery, and the knowledge that this metal would likely be extremely strong (hence
being named after mythological beings that embodied physical strength), it wasn’t until 120 years
later in 1910 when pure titanium would finally be produced.

In the past there was very little information about titanium’s machining characteristics, many
manufacturers were cutting blind and making parts through trial and error. Using hard metal 8

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techniques with tools made for aluminum on multipurpose machines created a process that was
costly, required constant monitoring, and produced unpredictable tool life.

Titanium Timeline:

1791 3 Discovery of the metal by William Gregor

1793 3 Confirmation and naming of the discovery by M.H. Klaproth
1910 3 Matthew A. Hunter develops a method to extract the metal from the ore
1938 3 William Kroll develops his method for extracting titanium
1947 3 Two tons of titanium produced
1948 3 The U.S. Government starts providing incentives to develop titanium manufacturing
1953 3 Annual production reaches 2 million pounds
1965 3 Per-Ingvar Brånemark places the first titanium dental implant
2010 3 Over 6 million tons being produced annually

1.1 TITANIUM ALLOYS:

Titanium alloys are grouped into four distinct types: commercially pure, alpha, beta, and alpha-
beta. Each of these forms of the metal provides specific benefits, which means that different alloys
will be used for different projects. Alloying elements are used to stabilize either the alpha or beta
phase, which can create different characteristics to address different needs and to create titanium
alloys that can be strengthened by heat treatment.

Alpha Alloys 3 These alloys are easy to weld and provide reliable strength at elevated
temperatures. They are created with neutral alloying elements and alpha stabilizers, such as
aluminum, but the results are not heat treatable.

Beta Alloys 3 These are the most common choices for projects that require higher tensile strength.
A beta alloy is also heat treatable and contains sufficient beta stabilizers to maintain their beta
phase even when quenched. Beta alloys use stabilizers like molybdenum or silicon, to create the
desired characteristics.

Alpha-Beta Alloys 3 These are the most commonly used alloys because they combine the best
characteristics of the other two alloys, creating a balance between strength, weight, and corrosion
resistance. These alloys are heat treatable and are made with both alpha and beta stabilizers.

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1.2 TITANIUM BREAKTHROUGH:

Matthew A. Hunter, working for Rensselaer Polytechnic Institute in cooperation with the General
Electric Company, suspected that the high melting point of titanium would make it a great
candidate for their new incandescent lamp filaments. However, their calculations on the melting
point were a bit off, and the project was abandoned, but because of their efforts, there was now a
viable way to extract the metal from the ore.

Hunter’s process involved mixing TiO2 with coke and chlorine. By applying heat to the titanium
dioxide, it would produce TiCl4, which could be reduced with sodium to create an alloying agent
that would, for another few decades, mostly be used as an alloying agent in steel. At this point, it
also became clear that the metal was a really good white pigment, and it became the choice for
white paints and other products.

However, while this process did work, it was not very useful or effective for larger scale
manufacturing. It wasn’t until 1938, when metallurgist William Kroll developed his method, that
widespread use became a real possibility. His process, called the Kroll Process, used magnesium
as the reducing agent instead of sodium and this is still the most widely used method today.

1.3 MACHINING OF TITANIUM:

Titanium has a number of characteristics that must be addressed in order to achieve effective
production rates and a good, clean surface finish. It’s important to understand those properties in
order to properly cut/drill/mill/polish titanium products. Some of the reasons milling must be done
with extreme care include:

Titanium can react with the cutting tools, which could lead to seizing, galling, and cause other
unwanted blemishes to the surface.

The low thermal conductivity of titanium leads to an unusual chip-forming tendency. This, in turn,
can cause an excessive buildup of heat on the cutting tools. Normally, the high temperatures would
dissipate in the chip (like it does with steel or aluminum). With titanium, all that heat is absorbed
by the cutting tool.

Titanium is a low elastic modulus, which means that it is harder to cut, and may cause deflections
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These special characteristics make milling titanium a very time-intensive process. This is also why
40% to 50% of titanium’s costs are directly related to machining. While there are some other
processes in development that could, in theory, increase production speeds, at the moment, it’s all
about using the right tools in the right way.

Producers must find a way to balance cutting speed, tool wear, and profitable sustainability. This
is not always an easy task, but there are some techniques and guidelines that make it easier to
manage. These include:

Maintain the tools 3 If a cutting tool loses its sharp edge, it can cause very poor results, slow the
process even further, and cause tearing and a bad surface finish. Dull machining tools can also lead
to more heat buildup, which will contribute to further wear. These instruments must be kept sharp
and in peak condition to extend their lifespan and produce consistent results.

Maintain high feed rates (and never stop feeding) 3 While cutting speed can be detrimental to
titanium milling, feed rate is not. While there are limits, of course, the manufacturer needs to keep
the highest rate of feed that will still deliver the expected results. Also, once a blade starts cutting
into the titanium, it is important to keep the metal moving. If a tool stays in moving contact with
titanium, it can cause hardening, smearing, or seizing.

Keep cutting speeds low 3 The cutting speed has a direct impact on the heat buildup in the tool.
Too much heat results in damaged tools and poor products. Slightly higher speeds are possible
with commercially pure titanium, but alloyed titanium requires lower speeds. Even a small increase
in speed can lead to problem with the tools, though, so this should be carefully maintained.

Use plenty of cooling fluid 3 In order to offset the amount of heat accumulating in the tool and on
the sample, generous amounts of cooling liquid need to be used. This liquid dissipates the heat and
carries away the chips. This will help protect the edge of the tool and ensure a longer usable
lifespan. Some tools use a through-spindle coolant that delivers the liquid right to the cutting edge
while others require a high-pressure coolant pump that will stop chips from welding to the cutting
edge.

Titanium Chemical Properties

The chemical element, titanium (Ti), has the atomic number 22 and an atomic weight of 47.90. It
belongs to the first transition group and has a number of similarities with silica and zirconium. In
lower oxidation states it has some similarities with chrome and vanadium as well. 11

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When it is exposed to air at high temperatures, titanium metal and its alloys will oxidize
immediately, forming a passive, but protective oxide coating. The same effect can be accomplished
with nitrogen, which creates a coating of titanium nitride.

This protective oxide coating then serves to protect the metal from further oxidation, meaning that
the first coat will appear quite readily, but anything that goes deeper will take a longer time.

Titanium is a thermodynamically reactive metal. It actually burns before the melting point is
reached, which is why melting must be done in a vacuum or other inert atmosphere. By eliminating
the oxygen, it is possible to heat it to the melting point without turning the metal to powder.

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CHAPTER 2

LITERATURE REVIEW

To have an in-depth and through knowledge of concern area of research and to find out the scope
of further extension of work, a study of literature is needed. The literature review was accomplished
through the study of various research papers, reputed journals and relevant books related to the
application of the cutting fluids in the machining of titanium alloys.

2.1 CURRENT STATUS OF RESEARCH

Cantero et al. [21] studied the drilling of the same alloy using TiN-coated tools at cutting speeds
Of 50 m/min and feed of 0.07 mm/rev. In this study, the concentration was on the quality of the
holes and tool wear. It was observed that attrition and diffusion wear led to tool damage over time.
Since drilling was done at dry conditions, high temperatures were reached, which was evident from
chip combustion. Chip combustion took place between 4 and 6 min of machining. It was observed
that parts of the tool coatings were lost due to heat.

Armendia et al. [22] compared the machinability of Ti6Al4V and Ti54M alloys under dry
machining using uncoated tools. Machining was done at constant feed of 0.1 mm/rev and depth of
cut of 2 mm at different cutting speeds of 60, 70, 80, 90, and 100 m/min. least tool wear was
observed at 60 m/min, almost similar amount of wear for both materials.

Armendia et al. [23] studied the machinability of three titanium alloys, namely, Ti6Al4V,
TIMETAL® 54 M, and Ti6246. Ti6246 showed highest tool wear due to its hardness. The other
two alloys had similar mechanical properties but TIMETAL® 54 M was more machinable.

Narutaki et al. [24] used flood lubrication of water-based emulsion while machining titanium alloys
with diamond tool. It was reported that cutting speeds of 3.33 m/s (200 m/min) were possible in
flood lubrication. It was emphasized that coolant plays a critical role in the process.

Nambi and Paulo [25] machined Ti6Al4V alloy using ceramic inserts containing 80% Al2O3 and
20% TiC. Cutting fluid containing 75%water was applied as a coolant compared to 95% of water
that is normally used with water-soluble fluids. But, in this study, higher content of oil was used
to improve the lubrication in machining. Machining was done at different cutting conditions with

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and without the application of the cutting fluid. Cutting speeds of 45, 90, and 135 m/min, feed rate
of 0.1, 0.2, and 0.32 mm/rev, and depths of cut of 0.5 and 0.75 mm were chosen.

Banerjee and Sharma [26] machined Ti6Al4V using uncoated cemented carbide tools for
machining of Ti6Al4V alloy at constant cutting conditions (speed = 76 m/min, feed = 0.24 mm/rev,
and depth of cut = 1 mm) and supplied the cutting fluid in three different directions at flow rate of
36 mL/h in each nozzle. Air pressure was maintained at 2.8 and 5.8 bar. The first nozzle supplied
the lubricant at the back of the chip, second nozzle on the rake face, and third nozzle on the flank
face. Both neat oils and water miscible cutting fluids were used and compared.

Duschosal et al. [27]. Performance of MQL was tested for different tools and inner channels in
milling cutter. The channels had orientations of 45°, 60°, and 75°. The internal channels helped in
the flow of the lubricant from a central channel to the cutting edge. Though the work concentrated
on finding the optimal channel orientation, it gave some interesting inference which can be used
forMQL of titanium alloys.

Kanyak et al. [28] compared dry machining, MQL, and cryogenic cooling in machining of three
different NiTi alloys.

Abbasi and Pingfa [29] studied four different types of cooling systems: flood lubrication with water
miscible fluids, neat oils, MQL and cryogenic cooling in machining Ti6Al4V alloys with coated
carbide cutting tools. Cutting temperatures, forces, and stresses on tool edge were observed.

Ahmed et al. [30] drilled titanium ASTM B265 grade 2 material with PVD-coated carbide inserts
under flood lubrication and cryogenic cooling at different speeds and feeds. Cutting temperatures,
thrust force, and surface roughness and hole quality (form features) were measured.

2.2 INFERENCES DRAWN FROM LITERATURE REVIEW

1. The study suggests that dry machining is suitable only for a small time. Average surface
roughness of about 2.5 μm was reported at the end of tool life.
2. At higher speeds, Ti6Al4V gave higher tool wear. It was noted that tool life was about 15
min for Ti6Al4V.

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3. Mechanical properties alone do not dictate the machinability. The difference in

machinability of the two alloys was attributed to microstructural changes due to heat
treatment. It was observed that β annealing of the alloys led to more tool wear and cutting
forces compared to other heat treatment processes. Also, it is advocated that as Ti54M has
finer micro structure, better machinability, and hence can be a good replacement of
Ti6Al4V in many applications.
4. It was observed that at lower speed conditions, the interactions of the tool and work piece
were not significant. Abrasion wear was found to be the major contributor of tool wear.
Since abrasion wear is mainly due to friction, it may be inferred that flood lubrication
cooled the work piece (evident by reducing diffusion wear), possibly by conduction and
convection, but did not provide the required lubrication.
5. Tool life has increased by over 30% with the application of cutting fluid compared to dry
machining. Though attrition and adhesion wear lead to the failure of cutting tool, the wear
was much less compared to the dry machining. In dry machining, diffusion wear was
higher due to higher temperatures. Better surface finish was observed with the application
of the cutting fluid. This was attributed to the lesser chances of adhesion wear. BUE was
not noticed in wet machining. Further, permissible speeds and feeds are much higher with
the application of cutting fluids.
6. Supply of the coolant at the rake face and back of chip were beneficial in terms of cutting
forces and surface finish. It was proposed that localized flow and control of the lubricants
in MQL is more beneficial than the regular strategy. Higher pressure was found to be more
advantageous. At the considered cutting conditions, neat oils were found to give better
performance compared to water miscible cutting fluids.
7. It was found the aerodynamic shape of the tool played a significant role in the cooling.
Also, it was found that pressure of the MQL jet had a major role in the lubrication.
8. It was found that cryogenic cooling resulted in consistently lesser tool wear compared to
dry machining and minimum quality lubrication.
9. Cryogenic cooling led to lowest cutting temperatures, forces, and stresses compared to
flood lubrication with water miscible fluids, neat oils and MQL.
10. Cryogenic cooling reduced the temperatures up to 59%; however, cutting forces were high
and poor hole quality was observed. The extreme cooling was supposed to have caused
dimensional/form inaccuracies.

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CHAPTER 3

SOLUTIONS TO OVERCOME MACHINING DIFFICULTIES

Due to the wide spread use of titanium alloys and their poor machinability, machining of the alloys
has received due attention. Various techniques are employed in machining of these alloys.
Figure 1 shows the classification of various approaches usually adopted in conventional machining
of titanium alloys. Different alloys of titanium are studied in the literature (Fig 2). Fig 2 gives the
percentages (w/w) of the elements present in the alloy, the rest of the composition being titanium.
It may be noticed that a majority of studies have concentrated on Ti6Al4V because of its wide
usage.

FIG 1: Classification of machining processes for titanium alloys [19]

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FIG 2: Tabular data for different titanium alloys studied by researchers [19]

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3.1 DRY MACHINING:

Dry machining refers to machining without the use of any coolant. Many times, dry machining is
encouraged due to the disadvantages of the coolants. However, dry machining results in high
cutting temperatures and cutting forces, leading to short tool life.

Various researchers have studied the efficacy of dry machining of different alloys having different
machinability levels [7]. Usually, coated tools are preferred over uncoated carbide tools for
machining of titanium alloys.

Almost all the reported works, dry machining of titanium alloys is characterized by high
temperatures and tool wear. It is generally reported that higher cutting speeds severely affect tool
wear/product quality. Hence, the permissible cutting conditions in machining the alloy are limited
for long tool life, leading to low productivity.

3.2 CUTTING FLUIDS:

The conventional approach to restrain cutting temperatures and associated problems is the
application of cutting fluids [8]. Cutting fluids are usually applied with the nozzle pointed at any
of the three different directions, namely, behind the chip, on the rake face, or on the flank face
(Fig. 3). The cutting fluid reaches the interface of the tool/chip through capillarity, forms a thin
film and prevents the adhesion of the chip on the rake face of the tool [9]. This reduces friction and
consequent heating. However, since the temperature is very high in the machining of titanium
alloys, the cutting fluid evaporates before it reaches the tool/chip interface. To compensate for the
loss due to evaporation, flood lubrication has been adopted in many studies.

FIG 3: Direction of application of cutting fluids [8]

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3.3 FLOOD LUBRICATION:

Flood lubrication is the conventional method of applying cutting fluids in machining. Typically,
flow rate of over 100 L/h is adopted. The cooling is mainly due to convention of the heat from the
machining zone and a small quantity of the coolant may reach the tool/chip interface, depending
on the direction of the coolant application. Among the various types of cutting fluids available,
generally, water-based emulsions are applied in flood lubrication due to the high heat transfer
capabilities and economy [8].

Though flood lubrication is usually sufficient for effective cooling in machining of titanium alloys,
high-pressure coolant delivery systems are preferred [10]. It is often reported that the low pressure
of regular coolant may not be sufficient to break through the vapour blanket formed by the
prevalent high temperatures and hence sufficient cooling may not be obtained. Since the increase
in flow rate and velocity of the jet increases the heat transfer coefficient, higher pressures result in
faster heat dissipation and are more advantageous. Further, pressurized jet helps in chip breaking
and prevents excessive contact of the chip with the rake face of the tool, thus reducing the friction.
It is interesting to note that even jet cooling may not completely lubricate the machining zone and
many times abrasion and diffusion wear of the tool were reported.

A study by Shokrani et al. [11], power consumption was estimated in both dry and flood lubrication
conditions while machining Ti6Al4V. It was stated that flood lubrication consumed 40% more
power compared to dry machining, due to the power consumption of the coolant pump. This is
contrary to the belief that cutting fluids reduce the cutting forces and hence power consumption. It
may be worth mentioning that the study used regular conventional flood lubrication and the
quenching of the work piece may have increased the forces and hence the power consumption.
This phenomenon is not very prominent in metals like steels, but for titanium alloys, where the
temperatures are very high, this is significant.

The study suggested that flood lubrication is not always economical. If only the power
consumption of the pump is considered, then high jet cooling requires more power than flood
cooling. Hence, carbon foot print evaluation of cutting fluids discloses several surprising facts.
Due to the associated problems, the use of cutting fluids is limited by different environmental
agencies and the industries are looking for alternatives to replace the cutting fluids, without
sacrificing the benefits [12].
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Cutting tools and cutting fluids (coolants) are under constant development to improve the
machining of such alloys. Dry machining has a limited range of permissible cutting conditions and
hence is not suitable for industrial production. Coolants remove heat and metal cuttings (chips)
from the cutting zone and provide lubrication. Usage of coolants mitigates certain health and safety
considerations whilst creating others. Prolonged exposure to coolant fluids and mist can cause
health issues. Alternatively, the ignition of dry titanium chips can cause fire. These risks must be
mitigated, to study this titanium alloys Ti-6Al-4V and Ti-10V-2Fe-3Al were machined, studying
the effect of three coolant application conditions in finish turning. The conditions were through-
tool delivery of emulsion coolant at 60 bar pressure, flood delivery of emulsion and cutting dry
with no coolant.

Tool wear tests assessed the surface speed at which 15 minutes tool life could be achieved. It was
found that dry turning could be run at between 70 and 80 percent of the speed achieved for through-
tool delivery. The flood conditions could achieve 88 to 92 percent of the speed achieved for
Through-Tool. Dry cutting performed well regarding tool wear, considering the reduction of
resource usage and reduced environmental impact. A weakness of dry and flood turning was that
chips formed problematic tangled structures.

FIG 4: Titanium cuttings (a) dry cutting, (b) flood lubrication, (c) 60 bar through tool [3]

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FIG 5: Tool Life data for Ti-10V-2Fe-3Al turned with flood lubrication [3]

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Delivery Method Coolant Flow rate V15 for Ti-6Al-4V V15 for Ti-10V-2Fe-3Al
(1/min) (m/min) (m/min)
Dry None 135 120
Flood 19.2 155 150
60 bar TT 16.5 170 170

Table 1: V15 surface speed for two alloys with three coolant conditions [3]

Individual turned Ti-10V-2Fe-3Al samples had their microstructure analyzed. For a sample
machined under dry conditions some sub-surface damage metrics were worsened whilst other were
improved, compared to samples turned using coolant. No evidence was seen of a burned surface.
Recommendations for future work includes taking more samples for microstructures analysis.
[3]

In case of challenges faced while drilling Ti-6Al-4V was drilled using graphene oxide suspended
cutting fluid. A new series of experiments were conducted to investigate the effects and working
mechanisms of the new fluids. Thermal conductivities of conventional coolant and the graphene
oxide suspended fluid was measured: the effects of different cutting parameters such as cutting
speed and feed rate were analyzed; thrust force, surface roughness, tool wear and the formation and
morphology of chips were discussed. To investigate the performance of graphene oxide suspended
cutting fluid, similar experiments were conducted with conventional coolant as well. A significant
reduction in cutting force of up to 17.21% and a dramatic improvement in surface roughness of
15.1% were achieved by using the new graphene oxide suspended cutting fluid.

FIG 6: Schematic drawing of the coolant system [4]

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 Thrust force increased when feed rate was increased. The higher the spindle speed, the
lower the thrust forces. Lower thrust force has been obtained in using graphene oxide
suspended fluid than conventional coolant. Under the same cutting condition, the reduction
of cutting force was up to 17.21%.
 Tool wear under GO suspended coolant was insignificant after32 drilling processes.
Adhesion of titanium chips at the cutting edge, and spalling of tool material caused by
tool/chip abrasion was found on the tool surface under CC coolant.

FIG 7: Tool wear under different coolant: (a) Conventional coolant; (b) Graphene
oxide suspended fluid [4]

 Through the examination of SEM and EDS images, it was found that the holes drilled with
graphene oxide suspended fluid had less thermal cracks than those drilled under
conventional fluid. The average surface roughness measured by using Alicona micro-
scope, under the same machining condition, was 15.1% less than when using conventional
fluid.

FIG 8: SEM images of hole surface machined with conventional coolant: (a) Hole
surface 150x; (b) Hole surface 500x [4] 21

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FIG 9: SEM image of chip formation under two different coolant: (a) Conventional
coolant; (b) Graphene oxide suspended fluid [4]

 When spindle speed was below 1600 rpm and feed rate was less than 0.12 mm/rev graphene
oxide suspended fluid resulted in excellent chips (spiral chip), while discontinuous chips
were formed when using conventional coolant. It was also found that free surface of the
chip formed in using CC coolant had thicker lamella. However, the chip lamella was much
filmy when GO suspended coolant was used. On the other hand, the back surface of the
chip generated CC coolant has flaws and material stuck, which illustrated that higher
cutting temperature was generated. Little material was stuck on the back surface of chips
when GO suspended coolant was applied. With the increase of cutting speed, the chip
thickness was reduced. The chips were generated thinner when GO suspended coolant was
used. [4]

Challenges faced during milling of titanium alloys for this experiments were conducted using
atomization-based cutting fluid (ACF) spray system in end-milling of titanium alloy, Ti36Al34V.
The study is divided in two phases. First phase, experiments have been carried out to select suitable
spray parameters. A numerical model of the ACF spray system has also been developed to gain a
physics-based understanding of the cutting fluid film formation on a rotating tool surface and its
role in providing cooling and lubrication at the cutting interface. In the second phase, experiments
have been conducted to compare the machinability of titanium for different cutting fluid
application methods, viz., dry cutting, flood cooling and ACF spray system, on the basis of five
machinability parameters, including, tool life, tool wear, cutting forces, surface roughness and chip
morphology. Experimental results show that the application of the ACF spray system results in
uniform tool flank wear, lower cutting forces and higher surface finish and the tool life extends up
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to 75% over flood cooling. Additionally, chip morphology analysis reveals that using ACF spray
system leads to the formation of shorter and thinner chips, as compared to those when flood cooling
is used. [5]

FIG 10: ACF spray system in milling setup [5]

FIG 11: Chip morphology when machining [5]

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3.4 MINIMUM QUALITY LUBRICATION:

Minimum quantity lubrication (MQL) is a strategy of applying low quantity of the cutting fluid as
coolant in machining. This eliminates the disposal issue as almost all the quantity of the fluid is
evaporated. Though flood lubrication was initially preferred in machining of titanium alloys due
to the high temperatures generated, MQL is slowly finding its way in to the field. MQL can be
applied in two forms, drop-by-drop or mist form, and the second one being popular. In the mist
method of application, the fluid is atomized by missing with compressed air and is applied as an
aerosol spray. This increases the surface area of the lubricant exposed to the work piece and helps
in better cooling. Further, cooling enhanced due to the high velocity of air and hence better heat
transfer coefficient of the air/lubricant mixture. Several brands of commercial equipment are
available in the market for regulating the flow rate and pressure of the applied lubricant.

Kolahdouz et al. [13] studied the surface integrity of gamma TiAl alloy machined in dry and MQL
conditions (semi synthetic oil at flow rate of 50 mL/h), with cutting speed of 600 m/min for MQL
and 300 m/min for dry machining, feed being constant at 0.005mm/tooth, and depth of cut as 5mm.
It was reported that MQL led to lesser energy consumption compared with dry machining and the
parts machined under MQL had better fatigue resistance, due to increased subsurface hardness.
Plastic deformation was observed in both cases of lubrication, but for MQL, the depth of
deformation was small. Also, MQL resulted in a better machined surface with lesser burrs.

Almost all the studies reported on application of MQL in machining titanium alloys, MQL was
found to be advantageous compared to flood and dry lubrication in terms of performance and
ecology. Lesser cutting forces, lesser temperatures, better tool life, and surface finish were
observed with the application of MQL. Use of MQL is highly recommended as this strategy
eradicates many of the environmental and disposal issues, especially when the cutting fluid is
vegetable oil based. Inclusion of micro/nanoparticles in the cutting fluids is found to increase the
performance of the cutting fluids in MQL. It may be noted that Nano fluids are not recommended
in flood lubrication due to the high cost and low biodegradability [14].

In order to achieve sustainable machining, different strategies for applying the cutting fluids are
developed. Some of the prominent methods include minimum quantity lubrication (MQL),
minimum quantity cooled lubrication (MQCL), and cryogenic cooling.

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Minimum quantity lubrication (MQL) is considered as an eco-benign, greener, and socio-economic

alternative to dry cutting. Nevertheless, its effectiveness is limited to mild cutting materials owing
to less generation of heat during machining. In order to address this challenge regarding hard-to-
cut materials, energy requirement, and material flow, Ranque-Hilsch Vortex Tube assisted
Minimum Quantity Cutting Fluids (RHVT-MQCF) has been practiced in the turning of pure
titanium and compared its effectiveness with conventional MQL cooling techniques. The turning
experiments were performed on pure titanium alloy by varying the cutting speed (250-300 m/min),
feed rate (0.05-0.13 mm/rev), and depth of cut (0.3-0.5 mm), respectively. In addition, a statistical
modelling technique and desirability function approach was used to analyse and optimize the
sustainable indicators for the machining process associated with the cutting force, power
consumption, specific cutting energy, chips morphology, material removal rate, and surface quality
(i.e. surface roughness). Regarding sustainability performance, Life Cycle Assessment (LCA)
model was applied using Simapro 8.3 software connected to EPS 2000 and ReCiPe Endpoint v1.12
databases.

FIG 12: Chip analysis under MQCF and RFVT-MQCF conditions at Cutting speed: 275
m/min, feed rate: 0.13 mm/rev & depth of cut: 0.5 mm under RHVT-MQCF conditions
[6]

Findings have depicted the high performance of RHVT-MQCF conditions regarding machining
characteristics compared to MQL under same conditions. In-depth analysis has shown that
RHVT-MQCF is a sustainable and useful alternative to the manufacturing sector. [6]
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3.5 CRYOGENIC COOLING:

Cryogenics is the science of study and application of materials below −150 °C. Nitrogen is
popularly used in this technique as it is abundant and non-toxic [15, 16]. In order to eliminate the
effects of heat and temperature in machining, liquid nitrogen is applied at −196 °C. The application
of liquid nitrogen at the low temperature (known as cryogenic cooling) carries away the heat and
also provides a cushioning layer between the tool/chip interfaces, thus reducing the friction.
Cryogenic machining is especially helpful to eliminate the failure of tool due to chipping and
plastic deformation. Cryogenic cooling is found to effectively reduce the cutting temperatures,
even at high cutting speeds. Further, the jet of cryogenic fluid helps to break the chip and thus
reduce the chip contact length. Lately, cryogenic cooling is gaining prominence in cooling titanium
machining process [17].

Deiab et al. [18] compared different lubrication techniques in machining of Ti6Al4V alloy. Dry
machining, flood cooling, MQL, MQCL, and cryogenic cooling were compared at different cutting
speeds (90 and 120 m/min) and feeds (0.1, 0.2 mm/rev). The coolants for MQL and MQCL were
prepared using rapeseed oil as a sustainable option. It was observed that while MQL/MQCL were
better at lower cutting speeds, cryogenic cooling was a better option at higher cutting speeds over
90 m/min (Fig. 13). Similar trends were observed in energy consumption and surface roughness.

FIG 13: Tool wear at different lubrications [18]

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From the available works, it can be seen that cryogenics demonstrate satisfactory performance in
terms of tool wear and cutting temperatures. However, extreme cooling causes some disadvantages
like hardening of the work piece. This is reported to cause increased cutting forces and poor
dimensional quality of the work piece. Hence, cryogenic cooling is not always looked upon as a
solution for cooling in machining of titanium alloys.

Fig 14: Summary of research on cryogenic cooling of titanium alloy [19]

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CHAPTER 4
APPLICATION & FUTURE SCOPE

4.1 APPLICATION

Titanium is widely distributed throughout the whole universe such as stars and interstellar dust.
After Al, Fe and Mg, titanium is the fourth most abundant of structural metals and is the ninth
most abundant element on the earth.

Titanium exists in most minerals such as ilmenite (FeTiO3); rutile (TiO2); arizonite (Fe2Ti3O9);
perovskite (CaTiO3) and titanite (CaTiSiO5).

Titanium offers a unique property spectrum owing to the combination of high strength, stiffness,
toughness, low density, and good corrosion resistance. These properties are enabled by a wide
variety of titanium alloys ranging from applications at very low to elevated temperatures.

4.1.1 AEROSPACE METAL INDUSTRY:

The aerospace industry is the largest user of titanium products. It is a useful material for
this industry because of its high strength to weight ratio and high temperature properties.
Titanium is typically used for airplane parts and fasteners. These same properties make
titanium useful for the production of gas turbine engines while it is also used for other parts
such as the compressor blades, casings, engine cowlings and heat shields.

FIG 15: Percentage of titanium in Boeing 787 [20]

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4.1.2 OCEAN ENGINEERING:

Titanium is appealing for ocean engineering applications because of its excellent corrosion
resistance feature. Therefore a great many of titanium products have been applied to the
desalination of sea water, as well as for vessels and exploration of ocean resources.
Submarines, bath vessels, atomic icebreakers, hydrofoils, hovercrafts, minesweepers and
propellers all have titanium in them.

4.1.3 MEDICAL DEVELOPMENT:

Titanium resists corrosion, is biocompatible and has an innate ability to join with human
bone, it has become a staple of the medical field, as well. From surgical titanium
instruments to orthopedic titanium rods, pins and plates, medical and dental titanium has
truly become the fundamental material used in medicine.

FIG 16: Titanium Knee joint [20]

4.1.4 AUTOMOTIVE:

In the field of automobiles, titanium found its first application within the engine parts of racing
cars early in the 1980s. Since then, the range of applications for titanium has expanded to
include its application in the muffler systems of super short-type bikes and limited models of
high-performance cars. Because of its great strength and low density, combined with virtual
immunity to corrosion in the automotive environment, titanium offers many attractions for use
in automobile applications. Despite its advantages, however, titanium hasn’t yet found a
widespread use because the automotive industry is very price sensitive. The cost of titanium is

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relatively higher than that for steel or aluminum alloys. However, for some applications
titanium is attracting great interest.

4.1.5 CHEMICAL:

According to a survey, in China, titanium is primarily used in chemical applications such as

heat-exchanger (57%), titanium anode (20%), titanium container (16%) and others (7%). In the
chemical industry, chlor-alkali and sodium carbonate are major consumers of titanium.

4.2 FUTURE SCOPE:

As the industry continues to develop, new trends and processes will affect how titanium is mined,
processed and milled. A lot of the current work is focused on bringing the costs of production more
into line with the other abundant metals that are used in so many applications. While the Kroll
Process has remained the most commonly used method to produce usable titanium, there is a lot
of interest in developing something that can surpass its abilities to produce titanium.

Some new alternatives have already appeared and are starting to gain more attention. The
Armstrong process and Fray-Farthing-Chen (FFC) Cambridge process have been under
development for some time now and are starting to get closer to industrial implementation.

Aerospace remains the main market for titanium, accounting for 60 to 75% of the titanium currently
being used. Even though a lot of the new generation of passenger aircraft is using a lot of carbon
fiber reinforced polymers, titanium will still be in very high demand because these fibers are
compatible with titanium but not with aluminum. In other words, the titanium will continue to be
part of high-value-added parts.

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CHAPTER 5

CONCLUSIONS

Titanium and its alloys are extensively used in different engineering and biomedical applications.
Among the available alloys, Ti6Al4V is used in a majority of the applications and a large quantum
of literature is devoted to the studies on this alloy. Based on the literature, the following conclusions
may be drawn:

1. Coated tools are preferred over uncoated tools due to better protection of the tool from
reacting with the work material. Uncoated tools are sometimes reported to have tool life
less than 1 min.
2. The composition of the alloy, microstructure, metallurgical phase of the material, and
method of processing of material greatly affects the machinability. Finer micro structures
leads to greater machinability of the alloys.
3. Due to poor machinability, low cutting speeds, feeds, and depths of cut are permissible in
machining of titanium alloys. Usually, speeds less than 60 m/min are preferred. Some
works have reported that cutting speed of 80 m/min is advantageous. Higher values of feed
lead to damaged surface and are not preferred. Depth of cut has to be kept low for increased
tool life. This leads to decreased productivity. Hence, several researchers have worked on
finding solutions to the problem.
4. Cutting fluids are conventionally used to cool the machining zone. However, low pressure
jets cannot penetrate through the vapour formed due to high temperatures.
5. Use of pressurised jet of cutting fluid is recommended in literature to reduce the
temperatures.
6. MQL is used as a strategy to cool and lubricate the machining zone. The reported works
advocate better performance of MQL compared to dry machining and flood lubrication.
The cutting fluid in the MQL reaches the tool/chip interface through capillarity and forms
a film at the interface. This helps in lubrication and reducing temperatures.
7. Addition of micro and nanoparticles was found to be advantageous compared to regular
fluid. Nanoparticles like CuO and Al2O3 and solid lubricants like graphite is found in
literature. However, due to high cost, the use of Nano fluids is often restricted.
8. MQCL is a variant of MQL which is reported to have promising results compared to MQL.
Better cooling capabilities help in reducing the problems associated with machining of
titanium alloys.
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9. Cryogenic cooling is an effective alternative to the cutting fluids/MQL. Better tool life and
surface finish of the product, lesser forces, etc. are observed with the use of cryogenic
cooling. Chip breaking is effective in cryogenic cooling and results in smaller chip contact
length, reducing friction.
10. Hardening effects of cool N2 jet lead to increased hardness of the work piece and hence
produces higher cutting forces. Further, cryogenic cooling causes issues like dimensional
inconsistencies and poor product quality due to extreme cooling.

Future work may be directed towards newer blends of lubricants for MQL and design of new tools
for sustainable machining of titanium alloys.

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