Manufacturing Engineering - Metal forming

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MANUFACTURING
ENGINEERING
MECHANICAL WORKING OF METALS
• Rolling
• Extrusion
• Forging
• Drawing
• Sheet Metal

INTRODUCTION – Scope of the course
Rolling Extrusion Wire drawing
Forging Sheet metal

INTRODUCTION – Scope of the course
SN Unit/Section Contents
1. Introduction Types of metal forming, Recrystallization, Flow stress
2. Rolling
Terminology, Rolling mechanism, Slip, Maximum
reduction, Roll pass design, Rolling defect
3. Extrusion & Drawing
Types of extrusion, Important formulas, Wire drawing
and tube drawing
4. Forging
Types of forging, forgeability, Analysis of forging,
forging defects, forging operations
5. Sheet Metal Punching,Blanking & other sheet metal operations.

INTRODUCTION – What is metal forming ?
Dough making Metal Forming

Application of force changes
the shape of metal
Force

Metal forming is a process in which
load is applied on the metal
inducing a stress “” such that
y


y <  < ut
Provided
• Low yield strength
• Good ductility
• Good malleability

Metal Forming
Hot working Warm working Cold working
Above recrystallization At recrystallization Below recrystallization
T > TR T = TR T < TR

INTRODUCTION – Recrystallization
Grains
Grain boundary

INTRODUCTION – Recrystallization
Work
Normal grains
Elongated grains
Rollers
Grain boundary
Grains

INTRODUCTION – Recrystallization temperature
According to ASM – “Recrystallization temperature is the approximate minimum temperature at which the
complete recrystallization of a cold worked metal occurs within a specified period of approximately one hour.”
TR = Recrystallization temperature = 0.4 to 0.6 X melting point

INTRODUCTION – Recrystallization temperature
Factors
affecting
TR
Prior small
grains
Type of
metal
Extent of
prior cold
work
f(t)
2nd phase
particles
Rate of
deformation

INTRODUCTION – Hot VS Cold Working
Hot Working Cold Working
Lesser force required Comparatively more force is required
Lesser surface finish Better surface finish
Lesser dimensional tolerance Better dimensional tolerance
Thorough cleaning is required all along Moderate cleaning is required
No residual stresses Residual stresses are prevalent
Strength depends (Vary) on temperature Strength increases due to strain hardening

INTRODUCTION – Flow stress
y


y = Yield strength
In materials science and engineering,
the yield point is the point on a stress-
strain curve that indicates the limit of
elastic behavior and the beginning of
plastic behavior. Prior to the yield
point, a material will deform elastically
and will return to its original shape
when the applied stress is removed.

A B C
Cold working
Further working
Load > (y)A
Load > (y)B

y


y = Yield strength
T = K T
n Flow curve equation
K = Strength coefficient
T = True stress
T = True strain
n = Strain hardening exponent (0-1)

Flow stress = Instantaneous value of stress (load) required to continue deforming the metal or basically keep the
metal flowing (Hence the name flow stress). “Flow stress is YIELD STRENGTH of a metal as a function of strain.”
L0
L
P
A0
A
Engineering stress = P/A0
True stress = P/A Instantaneous

FLOW STRESS IS TRUE STRESS IN THE PLASTIC REGION
T = K T
n
f = K T
n

Several flow stresses are operating
f = K T
n f = Average flow stress
f =
𝐾 𝑇
𝑛
𝑛+1
1.No strain hardening
f = y
2.At UTS
𝑻 = n
Governing conditions

ROLLING - Terminology
• Rolling is the process in which metals and alloys are plastically deformed into finished or semi-finished
products, by passing them between rotating cylinders (Called as ROLLS).
• Rolling is the most widely used mechanical working process.
• 75 % of total steel output is treated in rolling mills. Rest 25 % by other mechanical working processes.
Work
Rolls
Output

ROLLING - Terminology
Ingot
Bloom
Billet
Slab
Plate
Bar
Beam
Channel
150 X 150 OR 250 X 300 mm
t = 50 to 150 mm
b = 600 to 1500 mm
50 X 50 OR 125 X 125 mm
Sheet
Strip
Angle
Foil

ROLLING - Mechanism
v
v0
v1
h0
h1
v

ROLLING - Mechanism
v
v0 v1
h0 h1
v
V Top Roller = V Bottom Roller
(DN)Top = (DN)Bottom
Now, to avoid unbalanced forces, the diameter of top and
bottom roller should be same.
Viz. D Top = D Bottom
i.e N Top = N Bottom
h0 = Initial thickness of work
h1 = Final thickness of work
v0 = Initial velocity of work
v1 = Velocity of work after rolling
V = Surface velocity of rollers

ROLLING - Mechanism
∆h = Reduction in thickness = h0 – h1
l0 = Initial length of work
l1 = Final length of work
b0 = Initial width of work
b1 = Final width of work
 = Angle of bite = Angle subtended by
center of rollers over deformation zone.
v0 v1
h0
h1
v
LD

b0 b1

ROLLING - Mechanism
Assumptions
• Volume is constant
• Width is constant
h0 b0 l0 = h1 b1 l1
i.e
ℎ0
ℎ1
=
𝑙0
𝑙1
• Flow rate is constant
A0 v0 = A1 v1
h0 b0 v0 = h1 b1 v1
i.e
ℎ0
ℎ1
=
𝑣1
𝑣0
> 1
 = Angle of bite = Angle subtended by center of
rollers over deformation zone.
v0 v1
h0 h1
v
b0
b1
v1 > v0

ROLLING - Mechanism
Assumptions
• No extended push/pull required.
The work is simply pulled because of
friction between the rollers.
v > v0 (To pull the work)
i.e v > v0 < v1
 = Angle of bite = Angle subtended by center of
rollers over deformation zone.
v0 v1
h0 h1
v
b0
b1
v1 > v > v0

ROLLING - Mechanism
O
A
B

C
From triangle OAB,
Cos  =
𝑂𝐵
𝑂𝐴
BC =
ℎ0 −ℎ1
2
= ∆h/2
OB = OC – BC = R - ∆h/2
Now, Cos  =
𝑂𝐵
𝑂𝐴
=
𝑅 −∆h/2
𝑅
 = Cos -1 (
𝑅 −∆h/2
𝑅
) Angle of bite
h0 h1
∆h = h0 – h1
∆h/2
∆h/2
Point of contact
Maximum possible draft

ROLLING - Mechanism


P
P
P

ROLLING - Mechanism
P = Normal force
P = Tangential force (Frictional force)
In the limiting case,
P Sin  = P Cos 
 = Tan 
 = Tan-1 


P
P
P
If  > Tan-1 , The work will not enter the
Space between the rolls automatically.

ROLLING - Mechanism
v0 v1
h0
h1
v
LD

b0 b1
O
A
B
C
C
A = Arc length of deformation
= R  = Length of contact
A B = Length of deformation zone
= Up to which deformation
takes place
Now, AB = 𝑂𝐴2 − 𝑂𝐵2 = 𝑅2 − (𝑂𝐶 − 𝐵𝐶)2
= 𝑅2 − 𝑅 − ∆h/2 2 = 𝑅2 − (𝑅2 +
∆h2
4
− ∆h𝑅)
= 𝑅∆h −
∆h2
4

ROLLING - Mechanism
∆h2
4
<< 𝑅∆h
i.e AB = 𝑅∆h = Length of deformation zone = LD
Now, Tan  =
𝑨𝑩
𝑶𝑩
=
𝑅∆h
𝑅 −∆h/2
Again, ∆h/2 << R & hence can be neglected
i.e Tan  =
𝑅∆h
𝑅
OR Tan  =
∆h
𝑹

O
A
B
C
Tan  =
∆h
𝑹
 = Cos -1 (
𝑅 −∆h/2
𝑅
)
& Angle of bite

ROLLING - Mechanism
 = 30 to 40 for cold rolling of steel and other metals with lubrication on well-ground rolls.
= 60 to 80 for cold rolling of steel and other metals with lubrication on rough rolls.
= 180 to 220 for hot rolling steel sheets.
= 200 to 220 for hot rolling aluminium at 3500 C.
= 280 to 300 for hot rolling steel (blooms and billet) in ragged or well-roughed rolls.

ROLLING - Slip
v0 v1

h0 h1
Neutral Point

ROLLING - Slip
Lagging zone Leading zone
Neutral Point
The portion between entry and neutral point is
known as Lagging Zone.
The portion between neutral point and exit (Of
work being rolled between rollers) is known as the
Leading Zone.

ROLLING - Slip
Lagging
zone
Leading
zone
Neutral
Point
Lagging
zone
Maximum slip occurs at entry point where difference in
velocity between work (Velocity v0) and roller (Surface
velocity V) is maximum.
=
𝑉 −𝑣0
𝑉
X 100 , This is called Backward slip.
Leading
zone
Maximum slip occurs at exit point where difference in
velocity between work (Velocity v1) and roller (Surface
velocity V) is maximum.
=
𝑉 −𝑣0
𝑉
X 100 , This is called Forward slip.

ROLLING - Slip
Lagging
zone
Leading
zone
Neutral
Point
Neutral
Point
NO SLIP occurs that means pure rolling can be seen.
Minimum would be the contact area between the work and
the rollers.
= Maximum pressure
Pressure 
1
𝑆𝑙𝑖𝑝

ROLLING – Maximum Reduction


90 - 

90 - 
F
N
Total horizontal force acting in the direction of
motion of work = F Cos  - N Cos (90 - ) = RX
Now RX > 0 (Always)
i.e F Cos  - N Sin  > 0
i.e F Cos  > N Sin 
i.e N Cos  > N Sin 
i.e  > Tan 
Let  be the angle of friction,
Tan  = 
i.e Tan  > Tan 
For the component to get pulled
Under force of friction
Angle of friction is greater than
the angle of bite.



90 - 

90 - 
F
N
For the component to get pulled
For maximum possible reduction in thickness,
Cos  = (
𝑅 −∆h/2
𝑅
)
R Cos  = 𝑅 − ∆h/2
∆h/2 = R - R Cos 
∆h = 2 (R - R Cos )
h0 – h1 = ∆h = 2 (R - R Cos )
As  increases, Cos  decreases
& hence ∆h increases
 =  For maximum reduction

Now  = 
viz, Tan  = Tan 
i.e Tan  = 
i.e
∆h
𝑹
=  
∆hmax
𝑹
∆hmax = 2R

ROLLING – Force and power
FAvg
LD
Average rolling force = PAvg X Area
PAvg =
2
3
𝑓 1 +
𝐿
4ℎ
h =
ℎ0
+ℎ1
2

ROLLING – Force and power
Favg = Pavg X b X LD
Torque (T) = Favg X L
Rolling power =
𝟐 𝝅𝑵𝑻
𝟔𝟎
X n
b = Width of work
L = Length of deformation
 = arm factor
n = Number of rollers

ROLLING – Reducing rolling force
Reduce
Power
Reduce
Torque
Reduce FAvg
Reduce
rolling
force
Decrease
Yield
strength
Reduce
roller
radius
Reduce 
Reducing
front and
back
tension

Backup Rollers
Work
Actual Rollers

Front
Tension
Back
Tension

ROLLING – Cambering of Rolls
Fixed support
UDL
Bending of roll
Non-Uniform thickness
of desired outcome

ROLLING – Cambering of Rolls
Convex shaped rolls
Cambering of Rolls

ROLLING – Types of rolling mills
Types
2 High
Reversing
3 High 4 High Cluster Planetary Tandem

2 High Rolling mill

3 High Rolling mill
Tilting
table
1st Pass
2nd Pass

4 High Rolling mill

Cluster Rolling mill

Planetary Rolling mill

Tandem Rolling mill

ROLLING – Roll pass design
Top Roll
Bottom Roll
Neck Neck
Grooves
Groove

Passes
Breakdown OR
Roughing Leader Finishing

Breakdown passes

The famous
Oval-Square series

ROLLING – Defects
Defects
Surface based
Scale
Rust
Scratches
Cracks
Pits
Gouges
Internal structure
Wavy edges
Zipper cracks
Edge cracks
Alligatoring
Folds
Lamitations

ROLLING – How to make production report in a rolling mill

EXTRUSION – Understanding extrusion
Extrusion may be defined as the manufacturing process
in which a block of metal enclosed in a container is
forced to flow through the opening of a die.

EXTRUSION – Understanding extrusion
• Most widely used in the manufacture of solid
and hollow sections from non-ferrous metals
and their alloys.
• The initial material (raw material) in extrusion
is cast or rolled billet.
Billet
• Range of extruded items is very wide, rods
from 3 to 250 mm in diameter, Pipes of 20 to
400 mm diameter & wall thickness of 1 mm can
be extruded.
• Complicated shapes can be obtained.

EXTRUSION – Types of extrusion process
Plunger
Extruded component
Die opening
Raw material
Die
DIRECT/FORWARD Extrusion
• Motion of plunger & extruded
component is in the same direction.
• More friction between raw material
and die wall.
• Easier handling.
• Can’t extrude hard material.

Plunger
Extruded component
Raw material
Die
INDIRECT/BACKWARD Extrusion
• Motion of plunger & extruded component is
in opposite direction.
• Less friction between raw material and die
wall.
• Difficult to handle extruded component.
• Difficult to design since ram is hollow.

Direct
Load
Ram movement
Indirect

Glycerin,SAE oil,Liquid glass,Polymers
HYDROSTATIC Extrusion
Extruded component
Raw material
Hydrostatic fluid
Plunger Die
• Modification of forward extrusion,
now hard material can also be
extruded.
• Size of raw material is lesser.
• Pressure is uniform due to fluid
pressure.
• Container wall friction gets
eliminated.
• Not recommended for soft
material since leakage of
hydrostatic fluid will be there.

Raw material Desired outcome
R
A
M
IMPACT Extrusion

EXTRUSION – Important formulas
1. Extrusion stress (0)
0 = 𝒇 (
𝟏+𝑩
𝑩
) (1 – (
𝑨𝟏
𝑨𝟎
)B)
𝒇 = Average flow stress
B =  Cot  (Where  = coefficient of friction &  = Half die angle)
A1 = CSA of extruded component
A0 = CSA of raw material (Billet)
2

2. Extrusion Force (FE)
FE = (0 + Pf) X A0
Pf = Extra pressure required to overcome friction
A0 = Billet area (Raw materials’s)
FE = 0 X A0 (For backward extrusion, Pf = 0)
FE = K A0 ln (
𝑨𝟎
𝑨𝟏
) (Based on extrusion constant)
K = Extrusion constant – Based upon the type of extrusion, raw material etc.

3. Ideal Conditions (No friction viz.  = 0)
 = 0, B = 0
0 = 𝒇 (
𝟏+𝑩
𝑩
) (1 – (
𝑨𝟏
𝑨𝟎
)B) =
𝟏
𝟎
format
Applying L.Hospital’s rule,
0 = 𝒇 ln (
𝑨𝟎
𝑨𝟏
) and Extrusion force, FE = 0 X 𝑨𝟎
4. Extrusion ratio =
𝑪𝑺𝑨 𝑩𝒊𝒍𝒍𝒆𝒕
𝑪𝑺𝑨 𝒐𝒇 𝒆𝒙𝒕𝒓𝒖𝒅𝒆𝒅 𝒄𝒐𝒎𝒑𝒐𝒏𝒆𝒏𝒕
= (
𝑨𝟎
𝑨𝟏
)

EXTRUSION – Advantages & Drawbacks
Drawbacks Advantages

DRAWING
Drawing is a cold working process in which workpiece
(wire,rod,tube) is pulled through a tapered hole in a die
so as to reduce its diameter.
THIS
Converts to
THIS

DRAWING – Wire drawing
Die
Raw material
Lubrication box Draw
box

I II III IV
Die
Raw material
Lubricant
catchers
Rod
Wire
2

I
II III
IV
Zone I – No contact with work, lubrication is supplied to prevent wearing of die and work.
Zone II – Approach region/Contact region, drawing starts here. Cone shaped with angle 6 – 200+
Zone III – Determines the size of final outcome.
Zone IV – Relief/Safety/Exit zone. Also called back relief zone. It is provided with a back relief angle
which is about 25 - 300

DRAWING – Force and power
Let A0 = CSA of rod =
𝜋
4
d0
2
A1 = CSA of drawn wire =
𝜋
4
d1
2
Drawing stress (D) = 𝒇 (
𝟏+𝑩
𝑩
) (1 – (
𝑨𝟏
𝑨𝟎
)B) , The stress with which material is pulled.
If D > 𝒇 then it means exact shape can’t be drawn.
Therefore, D  𝒇
Drawing force = D X A1
Drawing power = Drawing force X Wire velocity
1. For maximum possible reduction,
D = 𝒇

DRAWING – Force and power
2. Under ideal condition,
 = 0 & B = 0
D = 𝒇 (
𝟏+𝑩
𝑩
) (1 – (
𝑨𝟏
𝑨𝟎
)B) = 𝒇 ln (
𝑨𝟎
𝑨𝟏
)
3. For maximum possible reduction under ideal condition,
D = 𝒇
1 = ln (
𝑨𝟎
𝑨𝟏
) i.e
𝑨𝟎
𝑨𝟏
= e = 2.72
% reduction in area would be =
𝑨𝟎 −𝑨𝟏
𝑨𝟎
X 100
= (1 -
𝑨𝟏
𝑨𝟎
) X 100 = (1 -
𝟏
𝑨𝟎
𝑨𝟏
) = (1 -
𝟏
𝟐.𝟕𝟐
)
= 63 %

DRAWING – Tube drawing
Die
Fixed
support
Mandrel
Raw material
Tube

DRAWING – Tube drawing
Types
No
Mandrel
Fixed
Mandrel
Floating
Mandrel
Moving
mandrel

Forging
Forging may be defined as a metal working process by
which metals & alloys are plastically deformed to
desired shape by the application of compressive force.
The only process used for
producing non-uniform cross
section components.

Forging
Why forged components have comparatively high strength-to-weight ratio ?
Casting Machining Forging

Forging – Types
Types
Based on load
Drop
Hammer
Press
Forging
Based on die used
Open
Closed
Semi-
closed

Forging – Types
Drop hammer Press Forging

Forging – Types
OPEN Die Forging
Forged component
Top Die
Bottom Die
Initial
Position
Final
Position

Forging – Types
CLOSED Die Forging
Forged component
Top Die
Bottom Die

Forging – Types
Semi - CLOSED
Die Forging
Forged component
Top Die
Bottom Die

Forging – Types
Raw material
Top Die
Bottom Die
Gutter
Forged component
Flash

Forging – Forgeability
Factors
affecting
Crystal
structure
Purity
Phase
Grain
size
Melting
point
Yield
strength
The term “forgeability” is the word used to
Express forging ability both qualitatively &
quantitively.
It can be defined as metal’s tolerance or
relative ability to deform before cracks
appear.

Forging – Analysis
Forged
component
Top die movement
Inward frictional force
Outward expansion force
Sticking friction model Sliding friction model
Barrell
Barrelling effect

Forging – Operations
Basic operations
Upsetting Heading Fullering Edging Drawing down Miscellaneous
Bending
Flattening
Blocking
Cut-Off
Piercing
Punching
Coining

Forging – Defects
Forging defects
Cold shuts/Laps Pitting Die shift Dents Hair cracks Flakes Decarburization

Sheet Metal
Sheet metal OR Press working may be defined as a
chipless manufacturing process by which various
components are made from sheet metal.
THIS
Converts to
THIS

Sheet Metal

Sheet Metal
Advantages
Small weight of fabricated
parts
High efficiency Size accuracy
High
productivity
No further
machining is
required mostly

Sheet Metal – Punching and blanking
Die
Sheet Metal
RAM
Die
BLANK
HOLE
Shear stress
HOLE = Outcome = Punching
BLANK = Outcome = Blanking
A
B C
D
Die size > Punch size

Sheet Metal – Punching and blanking
c c
A
B C
D
c
Brass 5% of t
Mild steel 6% of t
Hard steel 7% of t
Al 10% of t
t Optimum clearance = 0.0032 t 𝜏𝑆
𝜏𝑆 = Ultimate shear strength (Mpa)

Sheet Metal – Operations
Press
operations
Blanking Punching Notching Perforating Trimming Shaving Slitting Bending Squeezing

Sheet Metal – Energy in press work
Energy in press work or the work done to make a cut is given by ;
E = Fmax X punch travel
E = Fmax X K X t (K = % of penetration required to cause rupture & t = thickness of sheet metal)
To allow for energy lost in machine friction and in pushing blank through the die, The equation gets modified
E = Fmax X K X t X Cf
Cf = Factor accounting for the amount of extra energy required.

Manufacturing Engineering - Metal forming

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