ENMF 417 CONTENTS

Contents
1 Mechanical Properties 2

2 Overview of Manufacturing Processes 4

3 Surface, Tribology, and Measurements 8

4 Expendable Casting 12

5 Permanent Casting & Design for Casting 16

6 Introduction to Bulk Deformation and Forging 20

7 Forging Analysis 25

8 Rolling, Extrustion & Drawing 28

9 Orthogonal Cutting 34

10 Turning, Milling, and Drilling 37

11 Tool Wear, Machinability, Tool Materials 39

12 Non-Traditional Machining 42

13 Polymers (a.k.a Plastics) 45

14 Polymer Processes 50

15 Rapid Prototyping 55
15.1 Powder Metallurgy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

16 Sheet Metal Process 58

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ENMF 417 0 - Mechanical Properties

1 Mechanical Properties
Engineering Stress-Strain Curve
P
ˆ Engineering Stress: σ =
A0
l − l0
ˆ Engineering Strain: ε =
l0
σY
ˆ Young’s Modulus: E =
ε0
ˆ Ductility:
lf − l0
– %EL = × 100
l0
A0 − Af
– Reduction of area = ×
A0
100
ˆ Modulus of Resilience: (energy/vol)
Maximum amount of energy per volume
that a material can absorb while elastically
deforming
– Specific energy that material can store
elastically
1 σy2 J
– σ y ε0 = = 3
2 2E m

Poisson’s Ratio

lateral strain transverse

v= =
longitudinal strain Axial
Assumption: volume remains constant

True Stress-Strain Curve

P
ˆ True Stress (instantaneous): σ =
A
ˆ True Strain (long strain):
   
l A0
ε = ln = ln
l0 A
ˆ σ = Kεn
– K = strength coefficient
– n = strain hardening exponent

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ENMF 417 0 - Mechanical Properties

Temperature Effects
In general: ↑ T → ↑ Ductility ↑ Toughness ↓ σY ↓ σU

Work Deformation
 
J
ˆ u = specific energy (toughness) → strain energy density
m3
– Involves both height and width S-S curve
kεn+1
ˆ Work = u× volume → strain energy u = 1
n+1
ˆ Strength is related to the height of S-S curve
ˆ Ductility is related to the width of the S-S curve

Hardness
Directly related to other mechanical properties such as strength and wear resistance

Fatigue
ˆ Testing specimens under various states of
stress (combination tension and compres-
sion)
ˆ Various stress amplitudes (S): # of cycles
(N) it takes to cause total failure of the
speciment
Prevention of fatigue failures:
ˆ Shot peening
ˆ Polishing the surface
ˆ Minimize vibration

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ENMF 417 2 - Overview of Manufacturing Process

Creep
ˆ Permanent deformation due to static load
ˆ A typical creep curve usually consists of primary, secondary, and tertiary stages
ˆ The creep rate increase with increased temperature & applied load

2 Overview of Manufacturing Processes

Manufacturing: Transformation of raw materials to valuable products. (Production)

Block diagram of Manufacturing:

Inputs → Process → Output
ˆ Demand ˆ Design ˆ Consumer
ˆ Raw materials ˆ Fabricate ˆ Capital goods
ˆ $$$ ˆ IT ˆ Quality
ˆ Energy
ˆ HR
ˆ specifications

Product Realization
Needs (Market Assessment) → Specifications (Concurrent Engineering)
→ Design : conceptual design, detailed → Process planning → Prototyping
→ Manufacturing → shipping → Consumer Service → Recycle, reuse

Rule of Ten
The cost of engineering changes made increases by 10 times when changes are made at a later stage

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ENMF 417 2 - Overview of Manufacturing Process

ˆ To reduce: – Use less expensive materials

– Simplify – Alternative methods of mfg
– Larger tolerance – Use more efficient machines

Manufacturing Processes


Cutting

Molding
Raw materials → → Machining (Grinding, Polishing) → Heat treatment


Deformation

Powder Metallurgy
→ Joining or Assembly → Finish

Job Shop
Job shops: Small lot size < 100 Batch production: 100-5000
Small-batch production: 10-100 Mass production: > 100000

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ENMF 417 2 - Overview of Manufacturing Process

Materials
Metals Polymers
ˆ Steel ˆ Thermosets: Epoxy
ˆ Aluminum ˆ Thermoplastics
ˆ Silver – PS
ˆ Gold – PEPC
ˆ Bronze – PMMA
ˆ Titanium – ABS, Nylon

Ceramics Composites
ˆ Silica ˆ Wood
ˆ Silicon ˆ CFRP
ˆ GFRP

Material Properties
ˆ Mechanical Properties ˆ Physical Properties
– Strength – Density
– Toughness – Tm (Melting Temp)
– Ductility – Magnetic
– Stiffness – Optical
– Hardness – Electrical
– Damping (viscoelastic)
– Fatigue ˆ Chemical Properties
– Creep – Oxidation
– Impact – Corrosion
– Degradation
– Toxicity

Material Selection
Material Cost: Significant portion in overall products
Reduction of Material: Achieved by minimizing the volume
Require high strength-to-weight ratio
May lead to thin cross-sections and present some problems

Selection of Manufacturing Processes

Choice of manufacturing processes is dictated by

ˆ Characteristics of the workpiece ˆ Production volume

ˆ Shape, size, thickness ˆ Level of automation
ˆ Dimensional tolerances, surface finish ˆ Costs
ˆ Functional requirements

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ENMF 417 2 OVERVIEW OF MANUFACTURING PROCESSES

Thin Cross Section Difficulties

ˆ Casting & Injection Molding ˆ Machining
– Mold filling, dimensional accuracy
– Deflections, vibrations → chatter
ˆ Forging
– Require higher force due to friction
ˆ Welding
ˆ Sheet metals
– Causes wrinkling – Distortions due to thermal gradients

Thick Cross Section Difficulties

ˆ Casting/Injection Molding ˆ Sheet metals → hard to bend
– Slow cooling time ˆ Welding → Difficult to penetrate
– Porosity

Trends in Manufacturing
ˆ Industry 4.0 ˆ Global Integrations
– Cyber physical Systems (IoT) ˆ Knowledge economy → crowd funding
– Sensors, communications ˆ Shorter life cycle
– Clouds, AI ˆ Rapid prototyping
– Automations

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ENMF 417 3 - Surface, Tribology, and Measurements

3 Surface, Tribology, and Measurements

Surface
Important reasons to consider surface

ˆ Friction & wear

ˆ Safety
ˆ Aesthetic
ˆ Fatigue
ˆ Contacts
ˆ Mechanical integrity of materials

Surface Integrity
Topological aspects as well as mechanical and metallurgical properties and characteristics of surfaces
→ Influences the properties of the product

Surface Roughness
Surface finish: A subjective term
Surface roughness:
ˆ Arithmetic Average: Ra ˆ Root Mean Square (RMS): Rq
 s 
1X 1 r
Ra = y→ |y|dx 1 X 1
n l Rq = y2 = y 2 dx
n l
→ n = number of readings
→ y = vertical deviation from normal
surface
→ l = the specified distance

Tribology
Friction

ˆ Resistance to relative sliding between two

bodies under a normal load
ˆ Energy dissipation - generation of heat
ˆ Adhesion Theory of Friction: µ = µa + µp

→ µa = Adhesion
→ µp = Ploughing

F τ τ
ˆ Coefficient of Friction: µ = = =
N σ hardness

→ τ = shear stress
→ σ = normal stress

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ENMF 417 3 - Surface, Tribology, and Measurements

Wear

ˆ Adhesive wear: Due to adhesion between

interfaces
ˆ Abrasive wear: Caused by a hard &
rough surface sliding along another surface
by forming chips
ˆ Corrosive (oxidation) wear: Chemical
reaction between surface and environment
ˆ Fatigue wear: Surface subjected to cyclic
loading

Lubrication
ˆ Reduce friction and wear
ˆ Major variables between two surfaces slide against each other:
1. Contact Pressure
2. Relative speed
3. Temperature
ˆ Functions of metal working lubricants
– Reduce friction & wear – Cooling
– Improve material flow in tools & dies – Remove debris
– Act as thermal barrier & releasing agents
ˆ Mineral oil, natural oil, syntehtic fluids, compounded lubrication, coating, barrier, etc.

Surface Treatment
⋆ Shot peening: Workpiece surface is impacted repeatedly with a large number of balls

– Plastic surface deformation – Improves fatigue life

* work hardening – Other types: Laser, water-jet, ultra-
* compressive stress sonic peening
Roller burnishing
⋆ Case Hardening (carburizing)
⋆ Vapour deposition (PVD, CVD, Sputtering)
– Physical Vapour Deposition: Parti- – Chemical Vapour Deposition: Ther-
cles are physically depositied mochemical process to coat
* Vacuum deposition * Titanium tetrachloride (vapor), ni-
* Sputtering trogen, hydrogen
* Ion plating * Thicker than PVD
* 3 hrs heating, 4 hrs coating, 6 hrs
cooling

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ENMF 417 3 - Surface, Tribology, and Measurements

⋆ Electroplating
– Cathode: collector – Anode: donor

ˆ Anodizing: Oxidation process

ˆ Painting


 Improve resistance to wear, erosion

Control friction
⋆→


 Improve: lubrication, corrosion, oxidation, fatigue resistance

Modify surface texture

Metrology
ˆ Measurement of dimensions
ˆ Line graduated instruments
– Vernier callipers
– Micrometers
– Diffraction grating (LDV)
ˆ Coordinate measuring machine (CMM)
ˆ Micro/Nano scale measurements: Scanning electron, atomic force, scanning tunnelling
microscope.
ˆ Laser Doppler Vibrometer: Non-contact vibration measurements of a surface
– Output: continuous analog voltage proportional to the target velocity
– Helium-neon laser, Nd-YAG laser

Non-Destructive Testing
Ultrasonic

ˆ Anomolies absorb or delect the sound

waves, which are then detected as changes
in the waves.
– Imperfections: Holes, voids, delam-
ination, damage, debond, resin-rich,
poor areas

Radiography (x-ray)

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ENMF 417 3 SURFACE, TRIBOLOGY, AND MEASUREMENTS

Acoustic Emission

ˆ State of health is determined by sounds

made by an object in use or under load
ˆ ≥ 1 ultrasonic microphones are attached
to the object and the sounds are analyzed
using computer-based instruments

Eddy Current Inspection

ˆ Presence of flaws or material variations al-

ter the impedance in the coil
ˆ Type of flaw or material condition indi-
cated by the change.

Magnetic Flux Leakage (MFL)

ˆ Detects corrosion and pitting in steel struc-

tures, most commonly pipelines and stor-
age tanks
ˆ Powerful magnet is used to magnetize the
steel
ˆ Areas where there is corrosion or missing
metal, the magnetic field ”leaks”

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ENMF 417 4 - Expendable Casting

4 Expendable Casting
Shape, surface condition, dimensions, and tolerances will reflect mold properties

Essential elements of Casting Process

ˆ Workpiece → liquid form
ˆ Mould
ˆ Heat transfer (solidifies the liquid)
ˆ Cast parts
ˆ Foundary: Casting factory equipped for making molds, melting and handling molten metal,
performing the casting process, and cleaning the finished casting.

Furnaces
For making liquid metal

ˆ Induction Furnace: Small foundries ˆ Electric Furnace:

– High rate of melting
– Less pollution
– Medium to large foundaries

Basic Features of Molds

Sand Casting Molds:

ˆ Flask: Container
ˆ Mold: Cope (upper) and drag (bottom)
ˆ Pattern: Create mold cavity
ˆ Gating system: cup, spruce, runner
ˆ Riser: A source of liquid metal to compen-
sate for shrinkage

Basic Fluid Equations

ˆ Bernoulli’s theorem (based on Conser- ˆ Continuity Law
vation of Energy) Q = A1 v1 = A2 v2
p v2 – Q = flow rate
h+ + = constant
ρg 2g – A = area
ˆ Reynolds number
– p = pressure (
vDρ Re < 2000 = Laminar
– h = height Re =
η Re > 20000 = Turbulent
– ρ = density
– g = gravity – n = viscosity
– v = velocity – D = channel diameter

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ENMF 417 4 - Expendable Casting

Solidification Time  2
V
ˆ Chvorinov’s Empirical Relation: Solidifcation time = C
A

– C = constant – V = volume – A = surface area

ˆ High volume-to-surface area ratio casts solidifies slower
ˆ Riser Design:The solidification time of the riser must be slower than the solidification time
of the cast part

Effects of Cooling Rate

ˆ Affects its microstructure, quality, and properties
ˆ Faster cooling (steel) = fine grain
ˆ Slower cooling (plaster) = coarse grain

Directional/Single Cyrstalline Solidification

ˆ Conventional casting - metal structure is polycrystalline, susceptible to creep deformation
ˆ Directional Solidification - Reduce the number of grains formed and improve creep resis-
tance and thermal shock

Advantages of Casting Metals Disadvantages of Casting

ˆ Works for metals where other manufactur- ˆ Poor dimensional control (need post-
ing techniques aren’t compatible processing)
ˆ Imperfections: porosities caused by gas and
– High-carbon steel: contain carbides
contaminations
– Low-carbon steel: too soft
ˆ Shrinkage due to solidification
ˆ Large castings ˆ Poor surface texture (coarse surface finish-
ˆ minimize metal scrap ing)
ˆ any metal ˆ Poor grain size distribution (uniform cool-
ˆ complex shops (internal cavities or hollow ing rate required)
sections) ˆ Safety hazard (3D environment)
ˆ mass production ˆ Dirty, dangerous, difficult

Types of Metal Casting

ˆ Composite mold ˆ Expendable mold
ˆ Permanent mold
– Expendable pattern
– Die
* Lost-foam
– Gravity
* Investment
– Centrifugal
– Permanent pattern
* sound
* plaster
* shell
* ceramic

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ENMF 417 4 - Expendable Casting

Expendable Mold Casting

Molds must be destroyed in order to remove the casting

Permanent pattern casting

Sand Casting
ˆ Most prevalent method
ˆ Used to mold the sand mixture into the
shape of the casting
ˆ made of wood, plastic, or metal
ˆ Cores: To achieve the internal surface of
the part
ˆ Chaplet: Metal supports used to anchor
the core (same material)
ˆ Molds: Sand with a mixture of water and
bonding clay
(90% sand, 3% water, 7% clay to enhance
strength and/or permeability)

Shell Casting
ˆ Dump-box technique
ˆ A mounted pattern is:
1. Heated to a range of 175 ◦ C - 370 ◦ C
2. Coated with a parting agent (such as
silicone)
3. Clamped to a box or chamber
ˆ Box is either rotated upside down or sand
mixture is blown over the pattern
ˆ Can produce many types of castings, close
dimensional tolerances, good surface finish,
and at low cost
ˆ Application: small mechanical parts

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ENMF 417 4 EXPENDABLE CASTING

Expendable pattern casting

Evaporative Pattern Casting

ˆ AKA Lost-Foam Casting
ˆ Molten metal completely replaces the space
occupied by the polystyrene
ˆ polystyrene beads: 5-8% pentane (a
volatile hydrocarbon) are placed in a pre-
heated die, usually made of aluminum
ˆ Degradation products from polystyrene are
vented into the surrounding sand
ˆ Complex patterns may be made by bond-
ing various individual pattern sections us-
ing hot melt adhesive

Investment Casting
ˆ AKA Lost-wax Casting
ˆ A pattern is invested (surrounded) with the
refractory material
ˆ Wax patterns (recovered and reused) re-
quire careful handling (weak)
ˆ A tree: joined patterns to make one mold,
increases production rate
ˆ Suitable for casting high-melting-point al-
loys with good surface finish and close di-
mensional tolerances

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ENMF 417 5 - Permanent Casting & Design for Casting

5 Permanent Casting & Design for Casting

Permanent Mold Casting
ˆ Advantages: – High tooling cost
– Good dimensional control & surface
finish
– Rapid solidification → cold metal
mold. Results in a finer grain struc-
ture, stronger castings
ˆ Disadvantages:
– Limited to metals of lower melting
point (Al, Mg, Cu)
– Simple part geometries compared to
sand casting because of the need to
open the mold
– High cost of mold → best for auto-
mated high-volume production

Die Casting
ˆ Die: mold cavity
ˆ Molten metal is injected into a die under constant high pressure (7-350 MPa)
ˆ Molds made of: tool steel, mold steel, tungsten, and molybdenum
ˆ Single or multiple cavity
ˆ Venting holes and passageways in die
ˆ Formation of flash that needs to be trimmed

Hot Chamber Die Casting

ˆ Hot Chamber (Pressure of 7-35 MPa)
ˆ Injection system is submerged under the
molten metals (low Tm metals such as lead,
zinc, tin, and magnesium)

Cold Chamber Die Casting

ˆ Cold chamber (Pressure of 14-140 MPa)
ˆ External melting container for aluminum,
brass, and magnesium

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ENMF 417 5 - Permanent Casting & Design for Casting

Pros of Die Casting Cons of Die Casting

ˆ Pros of permanent mold casting + ˆ Same as permanent mold casting cons
ˆ Thin sections are possible

Casting Defects
ˆ Cold Shots: Splattering creates entrapped globules in the casting
– Solution: Use better pouring procedures and gateway design
ˆ Shrinkage Cavity: Internal void where molten metal is not available
– Solution:
* Proper riser design * Control shape (avoid abrupt changes in
* Use chills thickness)

ˆ Misrun: The casting has solidified before completely filling the mold cavity
– Solution:
* Fluidity of the material is insufficient * Pouring done too slowly
* Pouring temp is too low * Cross-section of cavity too thin

ˆ Cold Shut: Two portions of metal flow together without fusing

– Causes: Similar to misrun

ˆ Porosity: Small voids which occur in the final dendritic stucture of alloyed metals
– Solution: Avoid
* or reduce dissolved gases * Extended freezing if possible

ˆ Hot tearing (cracking): Casting is restrained from contracting by a mold

– Solution:
* Design mold properly (reduce mold * Extract die immediately after freezing
strength) * Control solidification

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ENMF 417 5 - Permanent Casting & Design for Casting

Chills
ˆ Reduce shrinkage and porosity with large
volumes of metal
ˆ Usually made of same material as the part

Shrinkage Casting Costs

Design for Casting

ˆ Minimize:
– Sharp corners, angles
– Sudden change in thickness
– Large flat areas
ˆ Allow shrinkage during solidification
ˆ Apply draft angle

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ENMF 417 5 PERMANENT CASTING & DESIGN FOR CASTING

Product Design Considerations

ˆ Riser ˆ Machining allowance
ˆ Geometric simplicity ˆ Shrinkage

Selection of Casting Processes

ˆ Quantity ˆ Accuracy ˆ Cost ˆ Automation
ˆ Surface finish ˆ Strength ˆ Size

Summary of Casting Process

Pros Cons

ˆ Large grain size

ˆ Cheap
Sand ˆ Poor surface finish
ˆ No size limitation
ˆ Low dimensional accuracy

ˆ Fast
Lost foam ˆ Better surface finish than sand ˆ PS foam (every casting)
casting

ˆ Expensive
ˆ Intricate shapes
Lost wax ˆ Part size is limited
ˆ Good surface
ˆ Long process

ˆ Excellent dimensional accuracy

ˆ Low melting point metal
Die casting ˆ High production rate
ˆ Expensive molds & machine
ˆ Small grain size, Thin sections

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ENMF 417 6 - Introduction to Bulk Deformation and Forging

6 Introduction to Bulk Deformation and Forging

Forming and Shaping
ˆ Significant change in dimensions and overall geometry.
ˆ Permanent (plastic) deformation of the metal work piece occurs under tension, compression,
shear, or combinations.
ˆ Classification:
– Working temperature: Hot, warm, cold
– Size and shape change

Cold Forming
ˆ Metal forming performed at room temperature (T < 30%Tm )
ˆ Plastic deformation: work hardening

ˆ σy ′ > σy , ˆ Ductility decreases

ˆ Materials suitable for cold work:
– Low yield stress
– Lower energy needed for plastic deforma-
tion
– High work hardening
– Respond well with annealing

Advantages Disadvantages
Better Accuracy Higher forces and power
Better surface finish Limitation in amount of forming
High strength Additional annealing for some materials is required
Hardness of the part Some materials are not capable of cold work
No heating is required

Hot Forming
ˆ Pre-heated material deformation
ˆ Above the re-crystallization temperature (T > 60%Tm )

– Al-alloys: 400-450 ◦ C – Steels: 925-1200 ◦ C

– Cu-alloys: 600-900 ◦ C – Ti-alloys 750-795 ◦ C

Advantages Disadvantages
Big amount of forming is possible Lower accuracy and poor surface finish
Lower forces and power Higher product cost
Forming materials with low ductility Possibility of warping during cooling
No work hardening/No annealing Surface quality rough, machining required.

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ENMF 417 6 - Introduction to Bulk Deformation and Forging

Why use Forming?

Forming can be preferable to casting due to

ˆ Geometrical: Components having significant different dimensions are difficult to cast (e.g.
long rails, thin sheets)
ˆ Microstructure:
– In forming → easier to control microstructure than casting
– Deformation process alleviates compositional gradients and inhomogenity of grain size
ˆ Refractory Materials: materials which have high melting points can not be processed by
casting

Bulk Deformation Process

Input: Bulk materials in a Process: Large plastic defor- Output: Work materials for
form of cylindrical bars and mation - Rolling, forging, extru- subsequent processes or final
billets, rectangular billets and sion, and wire and bar drawing products (net shaping)
slabs or elementary shapes under cold, warm and hot work-
ing conditions

Types of Bulk Deformation Processes

ˆ Forging - plastic deformation of workpiece ˆ Extrusion - Production of long lengths solid
by compressive forces or hollow products with constant-section
by pushing the material

ˆ Rolling - reducing thickness or changing

cross-section profile
ˆ Drawing - Production of long rod, wire or
tubing by pulling

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ENMF 417 6 - Introduction to Bulk Deformation and Forging

Forging
Differences in Grain Structure

ˆ Forged chain link features true grain flow to yield maximum strength potential of material
ˆ In contrast, grain flow in link made from plate is broken by machining and cask link has no
grain flow
Casting Forging
Temp Work is done above melting temp Below melting temp
Microstructure Isotropic Anistropic → undirectional fiber lines
Shape Complex shape Relatively simple shape

Open Die Forging

ˆ The simplest forging operation
ˆ A metal workpiece (blank) is placed be-
tween two flat dies, and reduced in height
by compressing it (upsetting or flat-die
forging)

Impression Die Forging

ˆ The workpiece takes the shape of the die tween the two dies.
cavity while being forged between two
shaped dies
ˆ Impression-die forging can achieve close
tolerance
ˆ Advantages compared to machining from
solid stock:
– Higher production rates, less waste,
greater strength
– Favorable grain orientation in the
metal
ˆ Flash: excess metal which is squeezed out
from the die cavity into the outer space be-

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ENMF 417 6 - Introduction to Bulk Deformation and Forging

F = Kp Yf A

→ F = forging load → Yf = flow stress → Kp = pressure multiplying

factor

ˆ Simple without flash 3-5

ˆ Simple with flash 5-8
ˆ Complex 8-12

Flow stress: instantaneous value of stress required to continue plastically deforming of material
(to keep flowing)
σY < Yf , σf < σf,U T S → Yf = f (ε, ε̇, T )
Power low: Yf = kεp (Holloman’s equation)

Progressive Die Design

Progressive die: High amount of plastic deformation/complex shapes
Connecting rod: In internal combustion engine

Edging: Distributes the material properly when

pre-shaping the blank
Blocking: Making the rough shape (blocker die)
Impression die: Final shape
Trimming: Removing flash

Why Progressive Die

ˆ Costs 50-75% more than single die ˆ Less:
ˆ Easier to trim – Force
ˆ High accuracy – Elastic deflection (spring back) after
deformation
– Die wear or breakage

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ENMF 417 6 INTRODUCTION TO BULK DEFORMATION AND FORGING

Flashless Forging
ˆ Precision forging process
ˆ Process control: special and more complex dies, precise control of blank’s volume and shape,
accurate positioning of the blank
– More demanding than impression die forging
ˆ Best suited to part geometries that are simple and symmetrical
ˆ to reduce the number of additional finishing operations (net-shape forming)
ˆ Higher forces required to obtain fine details on part
– Requires higher capacity equipment

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ENMF 417 7 - Forging Analysis

7 Forging Analysis
Open Die Forging
Due to friction:

Yield Criteria
ˆ Metals: Dislocations moving around
ˆ Polymers: Molecules sliding against each other
ˆ Difficult to characterize the start of plasticity (yielding)
– Work hardening etc. Changes constantly
ˆ τmax ≥ K Approximations required:
→ K = Shear Yield Strength
σy
→ Tresca (Max. Shear Stress): K =
2
σ
→ Von Mises (Distortion energy) K = √ = 0.57σy
3

Plane Strain (ε2 = 0)

Workpiece cannot freely move in direction 2:
σ1 + σ3
σ2 = when ε2 = 0
2

Plane Strain - Von Mises

2
Sub in plane strain: (σ1 − σ2 )2 + (σ2 − σ3 )2 + (σ3 − σ1 )2 = 2σy2 → σ1 − σ3 = √ σy = 1.15σy = Y ′
3

Forging Analysis (rectangular Piece)

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ENMF 417 7 - Forging Analysis

ˆ P = Forming pressure ˆ x = a distance between the centre and edge

ˆ Y = Yield of workpiece
ˆ µ = Coefficient of friction for tool/material ˆ F = Forging force
interface
ˆ h = Height of work piece Friction Hill Equation:
ˆ a = Width of work piece P = Y ′ e2µ(a−x)/h

Friction Hill Example

Force required for forging:
F = Pavg × 2a × width

Friction Hill:
σy = P = Y ′ e2µ(a−x) /h

ˆ P = forming pressure
ˆ Y ′ = yield criterion
ˆ µ =coefficient of friction for tool/material
interface
ˆ h =Height of workpiece
ˆ a =width of workpiece
ˆ x =a distance between the centre and edge
of workpiece

Sticking Friction
ˆ Forging metal begins to ”stick” to the tool surface µσy = K
 
a−x
ˆ The average forming pressure under conditions of sticking friction is given by: P = σy = Y 1 +
′
h

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ENMF 417 7 FORGING ANALYSIS

Forging Presses
ˆ Hydraulic ˆ Mechanical
– Load limited – Stroke-limited
– For constant low speed operation – 2.7MN 107MN
– Open die (125MN) and closed die – Forging parts with high precision
forging (450 730 MN)

Forging Defects
Surface cracking:

ˆ Increase web thickness to avoid

ˆ Internal defects due to an oversized billet
ˆ Die cavities are filled prematurely, materials flow past the filled region.

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ENMF 417 8 - Rolling, Extrusion & Drawing

8 Rolling, Extrustion & Drawing

Rolling
A bulk deformation process of reducing the thick-
ness or changing the cross section of a long work-
piece by compressive force applied through a set
of rolls.
ˆ Changes in the grain structure of cast or
of large-grain wrought metals during hot
rolling
ˆ Reduced grain size in metals for improved
strength and ductility
ˆ Hot rolling
ˆ Cold rolling: high strength plate & sheet
– plates > 6 mm thick
* Ship hulls
* boilers
* bridges
* heavy machines
– sheets ≤ 6 mm thick
* Aircraft bodies
* applicances
* beverage containers

Mechanics of Flat Rolling

→ ∆h = h0 − hf = µ2 R
R = radius of rolls

ˆ Vs < Vr
ˆ Vs = Vr Neutral point: No slip point.
ˆ Vs > Vr
ˆ L = Roll gap. Friction force
Higher friction & larger the roll radius → greater
maximum possible draft

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ENMF 417 8 - Rolling, Extrusion & Drawing

Rolling Equations (Simple)

p √
ˆ Length of contact: (Roll gap) L = R(h0 − h1 ) = R∆h
ˆ Roll force; F = LwYavg
– Ya vg = Average true stress
Kεn
ˆ Average flow stress: Ya vg =
n+1
FL
ˆ Roll per torque: T =
2
2πF LN
ˆ Total power (for two rolls): Power (kW) =
60000
– N = rpm


1
ε n
ˆ True strain: σ= kεn → kε dε
ε0

Reducing Roll Force

ˆ Roll force can cause significant:
– deflection – flattening of the rolls

ˆ Can be reduced by:

– using smaller diameter rolls – applying back and/or front tensions to
– rolling at elevated temp strip
– taking smaller reductions per pass (mul- – reducing friction at the roll-strip inter-
tiple passes) face

Various Roll Arrangements

Smaller diameter rolls are preferable for thin strips.
→ Can easily deflect, requiring other rolls to support

Three-high mill: Tandem rolling: Planetary mill:

Cluster (Sendzimir) mill: Four mill:

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ENMF 417 8 - Rolling, Extrusion & Drawing

Defects in Rolled Products

ˆ Caused by inclusions and impurities in the original cast material or by material preparation
and the rolling operation
ˆ Structural defects:
a) Roll deflections: wavy edges
– Low ductility:
b) Zipper cracks in the centre of strip
c) Edge cracks
d) Inhomogeneity → Non-uniform bulk deformation: Alligatoring

Extrusion
Compressive forming process in which the work metal is forced to go through a die opening is a
shape of desirable cross-section

ˆ Direct extrusion (Forward extrusion) ˆ Indirect Extrusion (Reverse or backward

extrusion)
– No relative motion at the billet-
container interface

Extrusion Examples
ˆ Solid, hollow and semi-hollow parts
ˆ Advantages:
– Variety of shapes but a uniform cross-section
– no waste of material

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ENMF 417 8 - Rolling, Extrusion & Drawing

Metal Flow in Extrusion

A) Homogeneous flow pattern

B) When friction along interfaces is high, a dead metal zone develops. High
shear area as the material flows into the die exit.

C) High shear zone extends farther back due to frictions

*By increasing T, the flow stress drops rapidly

Extrusion Force
ˆ Force depends on:

– Strength of the billet material – Friction

– Extrusion ratio D0 >> Df – Process (i.e. temp, speed)

Extrusion Analysis
Ideal deformation (no friction): → A0 = initial area
→ Af = extruded area
A0
ˆ Extrusion ratio: R = → L0 = travel distance
Af → F = Force
ˆ Energy dissipated in plastic deformation → p = extrusion pressure at the ram
(Extrusion Pressure): → Y = yield stress
 
A0 → α = die angle
p = u = Y ln = Y ln R
Af
ˆ Work = F L0 = pA0 L0

ˆ Ideal deformation
 with friction

tan α
p=Y 1+ [Rµ cot α − 1]
µ
 
2L
p = Y 1.7 ln R + (45◦ die ∠)
D0
ˆ Actual forces (empirical)
– Friction coefficient variation
– Stress flow is not uniform
p = Y (a + b ln R) , a = 0.8, b = 1.2 1.5

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ENMF 417 8 - Rolling, Extrusion & Drawing

Optimum Die Angle

ˆ Die angle: Important effect on forces in extrusion
1. Ideal work of deformation is independent of the die angle
2. ↓ Frictional work with ↑ die angle because length of contact at
the die interface increases
3. Redundant work caused by inhomogeneous deformation increases
with die angle

Die Angle & Orifice Shape

ˆ Optimum angle depends on work material, billet temperature, and lubrication
– Low die angle: surface are is large, leading to increased friction at die-billet interface,
which results in larger ram force
– Large die angle: More turbulence in metal flow during reduction (inhomogeneous
deformation), which increases ram force required
ˆ Shape of die orifice affects ram pressure
– Simplest shape = circular die orifice
– As cross-section becomes more complex, higher pressure and greater force are required

Defects in Extrusion
ˆ Surface cracking (tearing) ˆ Extrusion defect
– Occurs when extrusion temp., fric- – Draw surface oxides and impurities to-
tion, or speed is too high ward the centre
– Surface temp. rise significantly – Reduced by modifying the pattern

Chevron Cracking (internal defects)

ˆ Due to hydrostatic tensile stress at the centre line of the deformation zone
ˆ Similar to necked region in the tensile test

Drawing
ˆ The cross section of a long rod or wire is reduced or changed by pulling it through a die called
a draw die.
ˆ Extrusion: Material is pushed through a die
ˆ Drawing: Pulled through the die

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ENMF 417 8 ROLLING, EXTRUSTION & DRAWING

Drawing Analysis
ˆ Drawing stress (ideal)
 
A0
σd = Y ln
Af
 
A0
F = Y Af ln
Af
ˆ Drawing stress (with friction)
 "  µ cot α #
tan α Af
σd = Y 1 + 1−
µ A0

Drawing Practice
ˆ Usually cold working & round cross-sections
ˆ Cold-drawn pieces contains residual stress due to inhomogeneous deformation
ˆ Bar drawing: Large diameter bar and rod stock
ˆ Wire drawing: Small diameter stock - wire sizes down to 0.03 mm are possible
ˆ Annealing: ↑ ductility of the stock
ˆ Cleaning: Prevent damage to work surface and draw die

33 Soohee Park
ENMF 417 9 - Orthogonal Cutting

9 Orthogonal Cutting
Machining
ˆ Remove materials using tools to achieve de-
sired shapes
ˆ Conventional Machining Sharp Tools
– Turning
– Milling – Sawing
– Driling – Broaching
– Facing – Reaming

ˆ Abrasive:
– Grinding – Honing
– Polishing – Lapping

ˆ Non-traditional Machining
– Laser, e-beam
– EDM (Electrical Discharge Machin-
ing)
– ECM (Electro Chemical Machining)
– Waterjet - plastic, metals

Pros and Cons of Machining

Pros Cons

ˆ Dimensional Accuracy ˆ Can be expensive for large batches

ˆ Complex Shapes ˆ Waste of materials
ˆ Surface Finish ˆ Lubricants
ˆ Can process a variety of materials ˆ Can be longer compared to shaping
ˆ Can be economical for small batches ˆ May have adverse effects of surface integrity

Orthogonal (2D) and Oblique (3D) Cutting

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ENMF 417 9 - Orthogonal Cutting

Cutting Forces
Parameters affection forces: RPM, depth, width, feed-rate, tool geometries, work-piece, lubri-
cants, etc,...

→ Fn = Normal Force (normal to shear plane)

→ Fu = Friction Force
→ Fv = Normal Force (normal to tool face)
→ Ft = Tangential Force (cutting force)
→ Ff = Feed Force (Thrust force)
→ αr = Rake Angle
→ ϕc = Shear Angle
→ βa = Friction Angle
→ h = Depth of cutting
→ hc = Deformed chip thickness
→ vs = shear velocity
→ Cs = Specific Heat
→ Tr = room temperature
→ b = width of cut
→ M RR = b · h · v · ρ = Material Removal
Rate
Ps
→ Ts ∼ = Shear Temperature
→ F = Resultant Force M RR · Cs
→ Fs = Shear Force → F⃗ = F⃗f + F⃗t = F⃗u + F⃗v = F⃗s + F⃗n

Equations
Shear Force: Fs = F cos(ϕ + β − α) = Ft cos ϕ − Ff sin ϕ
Fs
Shear: τs =
As
bh
Area of Shear: As =
sin ϕ
Cutting Ratio/Chip Rate
(from velocity diagram):
vc sin ϕ h
= = = rc
v cos(ϕ − α) hc

cos α sin ϕ
Shear Velocity: vs = v Chip Velocity: vc = v
cos(ϕ − α) cos(ϕ − α)

Shear Power: Ps = Fs · vs ∼
= M RR · Cs · (Ts − Tr )
rc cos α
Shear Angle: ϕ = tan−1
1 − rc sin
 α
Ff
Friction Angle: β = α + tan−1
Ft
Ff → Fv = Ft cos α − Ff sin α
→ = tan x
Ft → Fu = Ft sin α + Ff cos α
→ x=β−α

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ENMF 417 9 ORTHOGONAL CUTTING

Fu
Friction Coefficient: µ = tan β =
Fv
h hc
Shear Plane Length: Lc = =
sin ϕ cos(ϕ − α)
Friction Power: Pu = Fu · vc
Total Power: Ptotal = Ps + Pu = Fs vs + Fu vc = Ft · v
Fu vc Fu rc
Specific Energy for Friction: uf = =
bhv bh
Fs vs
Specific Energy for Shear: us =
bhv
Total Specific Energy: ut = us + uf
τ sin(β − α)
Tangential Cutting Coefficient: Ktc =
sin ϕ cos(ϕ + β − α)
τs sin(β − α)
Feed Cutting Coefficient: Kf c =
sin ϕ cos(ϕ + β − α)

Trends
↑ velocity → ↑ energy ↑ α →↓ F

Theoretical Shear Angle with

Minimum Energy Principle: Shear plane angle ϕ adjusts itself to minimize energy
π β α
ϕtheoretical ∼ − + → Affect force & Power requirement, chip thickness, temperature
4 2 2

36 Soohee Park
ENMF 417 10 - Turning, Milling, and Drilling

10 Turning, Milling, and Drilling

Machining Category
ˆ Conventional Machining ˆ Abrasive Machining ˆ Non-Traditional Machin-
– Milling – Grinding ing
– Sawing – Polishing – EDM
– Turning – Lapping – ECM
– Broaching – Waterjet
– Drilling – Laser
– Boring
Single Point Machining
ˆ Workpiece is rotating
ˆ Single point tool is stationary
ˆ Turning/Facing

– Reduce outer diameter – Make flat surface

ˆ Boring
– To enlarge the hollow workpiece
– Typically bigger holes than drilling
F l3
– Deflection: δ = (Young’s modulus
3Ez
should be high)

Milling Machine
CAD → CAM → gcode → CNC → Part

Horizontal Vertical

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ENMF 417 10 TURNING, MILLING, AND DRILLING

f
C=
nN

→ C = feed per tooth (mm/tooth)

→ n = Rotational speed (rev/min)
→ N = # of tooth
→ f = Linear feed (mm/min) → feed rate
→ t = time
→ h ≈ c sin ϕ
→ ϕ=ω·t

38 Soohee Park
ENMF 417 11 - Tool Wear, Machinability, Tool Materials

11 Tool Wear, Machinability, Tool Materials

Drilling
ˆ Chisel Edge: induces plastic deformation
of the workpiece
ˆ Helix angle: < α is beter for plastic

Broaching

X
Total Depth of Cutting = Depth of each cut

Sawing

Tool Wear & Breakage

ˆ High localized pressure
ˆ High temperatures
ˆ Friction between chip & rake face and tool & newly cut surface
ˆ Adversely affect:

– Tool life – Dimensional accuracy

– Quality of machined surface – Economics of cutting operations

ˆ Solution: Optimal parameters (e.g., width, speed, rpm, tool materials, coolant)

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ENMF 417 11 - Tool Wear, Machinability, Tool Materials

Abrasion Wear (Frank Wear)

ˆ When the hard tool material wears away
ˆ Rubbing of the tool along the machined
surface

Tayler’s Equation
V · tn = C
Empirical equation of tool life: t = C 1/n V −1/n d−x/n f −y/n

→ V = Cutting speed
→ t = tool life
→ n = tool & workpiece materials variable
→ C = Constant
→ d = depth of cut
→ f = feed
→ Typical machining operation:
n = 0.15
x = 0.15
y = 0.6

Adhesion Wear
ˆ Soft workpiece material adheres to tools
ˆ BUE (Built up edge) at low speed
ˆ Solution:
– ↑ Speed (RPM)
– Sharp tool
– Cooling coolants

Diffusion Wear (Crater wear)

ˆ High temp at tool-chip interface
ˆ Chemical affinity between tool & workpiece
material

– Chemical reactions
– Binding material migrate to chip

ˆ Solution: Protective coating (titanium car-

bide, titanium nitride, aluminum oxide)

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ENMF 417 11 TOOL WEAR, MACHINABILITY, TOOL MATERIALS

Machinability
ˆ A relative measure of how easily a material can be machined
ˆ Longer tool life, lower force, better surface finish, easier chip disposal, high MMR (Material
removal rate) means good machinability
ˆ MR: Machinability rating
ˆ Example:
– AISI 1112 steel: MR (Machinability rating) = 1
– Titanium: MR = 0.2 (poor machinability)
– Aluminum: MR = 2 (good machinability)
Tool Materials
Important Properties
ˆ Toughness - avoid fracture ˆ Chemical stability and inertness (diffusion
ˆ Hot (high temp) hardness - resist abrasion wear)
ˆ Wear resistance
Materials
ˆ High Speed Steel (HSS) → Drill bits, and ˆ Diamond (Polycrystalline Diamond - PCD)
mills
– Polycrystalline: Random orienta-
– Cheap
tion of crystal structure
– High toughness
– Hardest material
– Low hardness
– ↓ friction
– Regrind & reuse
– ↑ wear resistance - expensive
ˆ Carbides (most common) – Non-ferrous metal due to high affinity
– WC (Tungsten Carbide) → Powder to carbon
metallurgy
– ↑ compressibe strength ˆ Cubic Boron Nitride (CBN)
– ↑ hardness
– Second hardest
– ↑ wear resistance
– ↑ wear resistance
– ↑ thermal conductivity
– ↓ toughness
– Lower toughness compared to HSS
– Chemically inert to iron & nickel
ˆ Ceramics/Cermets (Ceramic and metal)
– Aluminum Oxide (Alumina)
– ↑ wear resistance and hot hardness
– Chemical stability is better HSS &
carbide
– Used for finishing off harder steel
(turning)

Cutting
ˆ Reduces heat generation at shear and friction zones (coolants)
ˆ Reduce friction between tool and chip (Lubricants)
ˆ Aid chip removal
ˆ Protect from environmental corrosion
ˆ Types of cutting fluids: Oil and oil & water mixture (less usage)
ˆ Application: Flood, mist, and coating (minimum quantity lubrication [MQL])

41 Soohee Park
ENMF 417 12 - Non-Traditional Machining

12 Non-Traditional Machining
Apply non-traditional machining if:
ˆ The strength and hardness of the workpiece material are very high
ˆ Too brittle
ˆ Too flexible or too slender
ˆ The shape of the part is complex
ˆ Special surface finish and dimensional tolerance requirements
ˆ The temperature rise during processing and residual stresses developed in the workpiece

Mechanical
Pros Cons
ˆ Can process any materials (hard & brittle) ˆ Hard to control depth
ˆ No heat ˆ Not as accurate compared to conventional
ˆ No deflection machining

Ultrasonic
ˆ Material is removed by micro chipping or
erosion with abrasive particles
ˆ 20 kHz (Dentist Scaling)
ˆ Grains are in a water slurry
ˆ Best suited for hard and brittle materials

Abrasive Water Jet

ˆ Act as saw (pressure as high as 400 MPa
or 60 ksi)
ˆ Commonly used for variety of materials in-
cluding food & fabric processing
ˆ No heat is produced, no deflection
ˆ Powders are mixed (SiC or aluminum ox-
ide)

Chemical Machining
ˆ Typical semiconductor fabrication process
ˆ Printed circuit board, microelectronic com-
ponents
ˆ Often used for deburring process
ˆ Not environment friendly
ˆ Remove materials by chemical dissolution ˆ Pains, elastomer, plastics (PVC, PE, PS)
using etchant (acids or alkaline solutions) → Solvent (different from etchants)

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ENMF 417 12 - Non-Traditional Machining

Electrochemical Machining (ECM)

ˆ Reverse of electroplating
ˆ Shape tool is made of brass, copper,
bronze, or SS.
ˆ Electrolyte is a highly conductive inorganic
salt solution. Often used for nickel-based
aerospace components (turbine blades, jet
engine parts, nozzles)

Chemical Pros Chemical Cons

ˆ Process layer materials (printed circuit
boards) ˆ Require masks (CM)
ˆ Burr-free process ˆ Can be expensive
ˆ Can process very hard materials (e.g. ˆ Under cuts (CM)
Nikel-based alloys) ˆ Environmentally harmful process

Electrical-Discharge Machining (EDM)

ˆ Very common for delicate components
ˆ When a voltage is applied to the tool, a
magnetic field causes suspended particle
in dielectric fluid to concentrate and form
bridge for current to flow to the workpiece
ˆ Dielectric fluid work as insulator and act as
ˆ Spark erosion machining a flushing agent
ˆ Arc is produced and removes materials ˆ Limited for electric conducting
(erosion)

Wire EDM
ˆ Similar to contour cutting with a band saw

Pros Cons
ˆ Minimal forces ˆ Limited for electrically conducting work-
ˆ Delicate components pieces
ˆ Slow
ˆ Shaped electrodes (graphite, brass, and
copper) to forming, powder metallurgy
casting.
ˆ Electrode wear
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ENMF 417 12 NON-TRADITIONAL MACHINING

Laser Beam Machining

ˆ Highly focused optical energy
ˆ High density energy melts and evaporates
ˆ CO2 or Nd:YAG (neodymium: yttrium-
aluminum-garnet): metals
ˆ Excimer: plastics and ceramics

Laser Beam Machining

ˆ 50-200 kV to accelerate electrons (speeds
of 50-80% of the speed of light)
ˆ Produces X-rays
ˆ Requires vacuum

Pros Cons
ˆ Can process very small features (micro & ˆ Expensive (EBM)
nano-meter scale) ˆ Limited workpiece (EBM)
ˆ Very accurate ˆ Require vacuum (EBM)

Stent Manufacturing
Braiding or knitting thin metal wires.

44 Soohee Park
ENMF 417 13 - Polymers: Structure, General Properties and Applications

13 Polymers (a.k.a Plastics)

Derived from Greek ”Plastikos” - it can be molded and shaped

ˆ Cast, machined, minimal surface

ˆ Film, sheet, plate finishing rods, tubing

Characteristics of Polymers
ˆ Relatively low cost
ˆ Corrosion resistance and resistance to chemicals
ˆ Low electrical and thermal conductivity
ˆ Low Density
ˆ High strength-to-weight ratio, particularly when reinforced
ˆ Noise reduction
ˆ Wide choice of colors and transparencies
ˆ Complexity of design possibilities and ease of manufacturing

Structure of Polymers
ˆ Polymer (poly - ”many” + mer ”part)
ˆ Repeated in a chainlike structure formed by polymerization reactions
ˆ monomer: Basic building block of a polymer.
ˆ Most monomers are organic materials (C-C), in which carbon atoms are joined in covalent
(electron-sharing) bonds with other atoms
ˆ 2 polymerization processes are important: condensation & addition polymerization
ˆ The polymer chains held together by secondary bonds, such as van der Waals bonds, hydrogen
bonds, and ionic bonds.

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ENMF 417 13 - Polymers: Structure, General Properties and Applications

Molecular Structure of Various Polymer

Polymerization Reactions

46 Soohee Park
ENMF 417 13 - Polymers: Structure, General Properties and Applications

Polymer Chains
a) Thermoplastics: acrylics, polyethylene, ny-
lons, PVC

b) Thermoplastics: polyethylene
- Green: resistance to deformation
Lower density than linear polymer

c) Thermosets and rubbers, elastomer, vul-

canized rubber
- 3 dimensional structures

d) Thermosets: epoxies, phenolics

Crystallinity
ˆ Amorphous: The polymer chains exist
without long-range (spaghetti like)
ˆ Crystalline: The polymers are formed
when the long molecules arrange them-
selves in an orderly manner.
ˆ The higher the crystallinity → harder,
stiffer, and less ductile the polymer
ˆ Optical Properties:
– Opaqueness comes from the boundary
between amorphous and crystalline

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ENMF 417 13 - Polymers: Structure, General Properties and Applications

Behavior of Polymers

Glass-transition Temperature
ˆ Glass-transition temperature Tg , also
called the glass point or glass temperature
at which a transition occurs.
ˆ Tg a plot of the specific volume of the poly-
mer as function of tempearture is produced
ˆ Tg occurs where there is a sharp change
in the slope of the curve.

Types of Polymers
ˆ Thermoplastic
– Reversible
– Weak secondary bonds
– Increase temp, weakens the secondary bonds
– Examples: acrylics, ceullulosic, PE, PS, PVC
ˆ Thermosets
– Long chain molecules are cross-linked in a three-dimensional arrangement
– Strong covalent bonding
– Non-reversible
– Curing (cross-linking) reaction
– Examples: epoxy, polyester, urethane

48 Soohee Park
ENMF 417 13 POLYMERS (A.K.A PLASTICS)

ˆ Elastomers (Rubber)
– Comprise a large family of amorphous polymers
– Low glass transition temp
– Undergo large elastic deformation without rupture (low E)
– Can be cross-linked (vulcanization) - cannot be reshaped (i.e., tire) (named after Vulcan
- Roman God of fire)
– Hardness increase with cross-linking of molecular chain
ˆ Reinforced Plastics (Composites)
– Offer outstanding properties for aircraft, offshore structure, piping, electronics, cars,
sporting goods
– Combination of two or more chemically distinct and insoluble phases
– Increase strength, stiffness and creep resistance
– Examples: glass, graphite fibers

Vulcanization
ˆ Natural rubber deteriorate after a few days
ˆ Due to sunlight and UV, polymer molecules are linked to other polymer molecules by atomic
bridges and more resistant to chemicals, etc.
ˆ Actual chemical cross-linking is done by heating the rubber with sulfur
ˆ Vulcanization can be defined as the curing of elastomers; the terms ’vulcanization’ and ’curing
are used interchangeably.

General Recommendations for Plastic Products

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ENMF 417 14 - Polymer Processes

14 Polymer Processes
Characteristics

Different Materials
TP: Thermoplastic TS: Thermoset E: Elastomer

50 Soohee Park
ENMF 417 14 - Polymer Processes

Extrusion
For continuous production of products.

ˆ Raw materials: thermoplastic pellets

granules, powders
ˆ Feed zone: Convey materials
ˆ Melting zone: Heat generated by shear-
ing of plastic pellets
ˆ Friction heat: Additional shearing &
pressure building

Die design

ˆ Polymer will swell at the exit of the die.

ˆ Openings are smaller than the extruded
cross sections.

Reinforcing Fibers

ˆ Melt-spinning process: Produces polymer fibers, used in fabrics

and as reinforcements for composite materials
ˆ Spinneret: Has one to several hundred holes. Polymers are pushed
through.
ˆ Stretching box: Right roll rotates faster than the left roll.

Injection Molding
Similar to hot-chamber die casting. For the production of plastic parts.
a) Hydraulic plunger
b) Rotating screw injection molding

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ENMF 417 14 - Polymer Processes

Sequence of Operations

Build up polymer in front of sprue bushing; pressure pushes the screw

backward

When the mold is ready, the screw is pushed forward by a hydraulic

cylinder

After polymer is solidified/cured, the ejector pins remove the molded

part

Process Capabilities
ˆ Versatile process capable of producing complex shapes, with good dimensional accuracy
ˆ Mold design and the control of material flow in the die cavities are important factors
ˆ Defects observed in injection molding are similar to those in metal casting
ˆ Shrinkage (1.5 ∼ 7%) for thermoplastics

Mold Features

Types of molds:

ˆ Two-plate mold ˆ Three-plate mold ˆ Hot-runner mold

(cold runner) (cold runner)

Reaction Injection Molding

Epoxy polyurethane (bumpers, fenders, steering wheels, instrument panels)

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ENMF 417 14 - Polymer Processes

Rotational Molding

ˆ Thermoplastics or thermosets with curing

agents
ˆ Large and hollow parts

Thermo-Forming Methods
ˆ Packaging containers ˆ Trays for cookies and ˆ Advertising signs
candy

a) Heater
a) Clamp
a) Plastic sheet
a) Mold
a) Vacuum line

Blow Molding
ˆ Combines continuous extrusion and mold-
ing
ˆ Modified version of extrusion and injection
molding
ˆ Plastic beverage bottle, hollow containers
ˆ Parison: Small tubular piece

Pros and Cons of Polymer Process

Advantage Disadvantage

ˆ Very economical for mass production ˆ Expensive die & molds

ˆ Comparable strength & toughness ˆ Sensitive to temp. & UV light
ˆ Light ˆ Thermoset → cannot recycle
ˆ No need to paint ˆ Environmental concerns

53 Soohee Park
ENMF 417 14 POLYMER PROCESSES

Design Modifications to Avoid Distortion

a) A high coefficient of thermal expansion is important factors

a) Stiffening the bottoms of thin plastic containers by doming
a) Design change in a rib to minimize pull-in (sink mark caused by shrinkage during the cooling
of thick sections in molded parts

Design Guidelines for Plastic Processes

ˆ Avoid sharp corners
ˆ Use uniform wall thickness
ˆ Use draft angles
ˆ Use ribs to improve part stiffness and minimize warpage
ˆ Consider shrinkage

54 Soohee Park
ENMF 417 15 - Rapid Prototyping and Powder Metallurgy

15 Rapid Prototyping
ˆ Capital cost for developing new products is high due to time and production tooling.
ˆ Before mass production, a working prototype is required for design evaluation and trouble
shooting.
ˆ Rapid Prototyping: Speeds up the iterative product-development process considerably
ˆ AKA Desktop or digital manufacturing, or solid free-form fabrication

Rapid-prototyping Processes & Materials

ˆ Subtractive: removing material from a ˆ Virtual: using advanced computer-based
workpiece that is larger than the final part visualization technologies
ˆ Additive: building up a part by adding ˆ Polymers: are the most commonly used
material incrementally material today, followed by metals and ce-
ramics

Additive Rapid-Prototyping
ˆ Stacking and bonding individual slices which are typically 0.1 - 0.5 mm thick
ˆ All additive operations require dedicated software
ˆ Obtain a 3D CAD (IGES) file, then the software constructs slices of the 3-D part (STL)

ˆ Fused Deposition Modeling (FDM): ˆ Stereolithography (SLA): Cures (hardens)

3D-printer a liquid photopolymer into a specific shape

ˆ Laminated Object Manufacturing:

– Desired shapes are burned into the sheet

with a laser, part is built layer by layer
– Lamination implies: laying down layers
that are bonded adhesively to one an-
other

ˆ Selective Laser Sintering: Based on the

sintering of nonmetallic or (less commonly)
metallic powders selectively into an individ-
ual object.

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ENMF 417 15 - Rapid Prototyping and Powder Metallurgy

ˆ Inkjet Based 3D Printing: Deposits an in-

organic binder material onto a layer of poly-
mer, ceramic, or metallic powder (instead of
ink)

Advantages of RP Disadvantages of RP
ˆ Reduce product development time & cost ˆ Part acccuracy - staircase appearance
ˆ Get products to market soon ˆ Shrinkage
ˆ Enhance communication between other de- ˆ Limited materials
partments ˆ Often time consuming
ˆ Present physical model at design review ˆ Water absorption
ˆ Perform functional prototype testing be- ˆ Sensitive to UV light & heat
fore tooling
ˆ Generate precise production tooling

15.1 Powder Metallurgy

ˆ Make complex parts by compacting metal powders in dies and
sintering them to net - or near-net-shape products
ˆ Sintering: Heating without melting, compacted metal powder
heated to a temperature below melting point (70 ∼ 90% of Tm )

Solid state material transport Vapor-phase material transport

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ENMF 417 15 RAPID PROTOTYPING

Situations for PM PM Process (Compaction)

ˆ Melting point of a metal is too high
ˆ Unwanted reaction occurs when melting a
metal
ˆ To control porosity
ˆ To mix different metal powders

Examples
ˆ WC inserts for machining tools
ˆ Balls for ball point pens and bearing
ˆ Graphite bushings impregnated by copper
ˆ Magnetic materials
ˆ Automobile parts
ˆ Surgical implants

Pros and Cons of PM

Advantage Disadvantage

ˆ A wide range of powder compositions ˆ High cost of tooling & powder materials
ˆ Near net shape ˆ Powders are difficult to handle
ˆ No waste ˆ Size limitation
ˆ Control porosity ˆ Density variations
ˆ Dimension control better than casting

57 Soohee Park
ENMF 417 16 - Sheet Metal Process

16 Sheet Metal Process

ˆ Usually performed as cold working
ˆ Sheet metal = 0.4 (1/64) to 6 mm (1/4 in) thick
ˆ Processes: ˆ Typical parts:
– Cutting (Shearing) – Car bodies
– Bending – Aircraft fuselages
– Drawing – Trailers
– Stretch Forming – Appliances
– Spinning – Cookware

Sheet Metal Characteristics

ˆ High ratio of surface to thickness
ˆ Avoid: Thickness decreases in sheet metal → leads to necking and failures
ˆ A specimen undergoes uniform elongation up to UTS, followed by further nonuniform elon-
gation (post-uniform elongation), until the specimen fractures
ˆ Factors affecting sheet metal:

– Yield-point elongation
– Lüders bond:
* Observed in low carbon steel
* Can be minimized by cold rolling
0.5 - 1.5 % in thickness
– Anistropy (directionality):
* Grain size
* Residual stress (non-uniform deforma-
tion)
* Spring back (significant in bending)
* Wrinkling (deep drawing)

Shearing

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Shearing (Cutting)

ˆ Edge quality can be improved by punch

speed: high shear rate
ˆ Burr increases with increasing clear-
ance and ductility of metal

Other Shearing Operations

ˆ Cutoff ˆ Parting ˆ Slotting

ˆ Perforating ˆ Notching ˆ Fine Blanking

ˆ Trimming: ˆ Shaving:
Punching away excess materials Improve accuracy of finished part

Bending
ˆ V-bending ˆ Edge Bending

Cracks due to Rolling Direction

Choosing the proper direction of bending is important

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Springback
Due to elastic recovery

(
= 1, No spring back
Ks Spring back factor =
= 0, Complete elastic recovery

ˆ Amount of recovery is based on E (Young’s Modulus)

ˆ After springback:
→ αf < αi
→ Rf > Ri

Compensation for Springback

ˆ Over-bending ˆ Stretch bending - subject ˆ Coining - High localized stress

to tension

ˆ Elevated temp. - decreases yield stress

Stretch Forming Spinning

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Deep Drawing
Process Defects (wrinkling & cracking)

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