Bulk deformation processes are metal forming operations that cause significant shape change through plastic deformation of initially bulk metal parts like bars, billets, and slabs. The main bulk deformation processes are rolling, forging, extrusion, and drawing. Rolling reduces the thickness of metal by passing it through opposing rolls. Forging shapes metal by compressing it between dies under impact or gradual pressure. Extrusion forces metal through a die opening to take on its cross-sectional shape. Drawing reduces the diameter of wires or bars by pulling them through a die. These processes are commonly done hot to facilitate greater plastic deformation.

1. BULK DEFORMATION
PROCESSES
IN METALWORKING
Ch# 19 By: Groover
1

2. Bulk Deformation
Metal forming operations which cause
significant shape change by deformation in
metal parts whose initial form is bulk rather
than sheet
Starting forms are cylindrical
bars,billets,slabs etc.
These processes work by stressing metal
sufficiently to cause plastic flow into desired
shape
Performed as cold, warm, and hot working
operations
2

3. Cold and warm working is suitable when shape
changes is less severe and need to improve
mechanical properties and good finish.
Hot working is required when massive
deformation of large work involved.
Importance of bulk deformation processes:
 In hot working, significant shape change can be
accomplished
 In cold working, strength can be increased during
shape change
 Little or no waste - some operations are near net
shape or net shape processes
 The parts require little or no subsequent machining
3

4. Four Basic Bulk Deformation
Processes
1. Rolling – slab or plate is squeezed between
opposing rolls
2. Forging – work is squeezed and shaped
between opposing dies
3. Extrusion – work is squeezed through a die
opening, thereby taking the shape of the
opening
4. Wire and bar drawing – diameter of wire or bar
is reduced by pulling it through a die opening
4

5. Rolling
Deformation process in which work
thickness is reduced by compressive
forces exerted by two opposing rolls
The rolling process (specifically, flat rolling)
5

6. The Rolls
The rotating rolls perform two main
functions:
1. Pull the work into the gap between
them by friction between work-part and
rolls.
2. Simultaneously squeeze the work to
reduce cross section .
6

7. Types of Rolling
 By geometry of work:
◦ Flat rolling - used to reduce thickness of a
rectangular cross-section
◦ Shape rolling - a square cross-section is
formed into a shape such as an I-beam
 By temperature of work:
◦ Hot Rolling – most common due to the large
amount of deformation required
◦ Cold rolling – produces finished sheet and
plate stock
7

8. Soaking Pits: for steel desired temperature for
rolling is achieved around 1200°C.the heating
operation is called soaking and furnace is called
soaking pits.
Bloom: has a square cross section
150mm*150mm or larger.
Slab: is rolled from ingot or bloom and has
rectangular shape width of 250mm and
thickness 40mm or more.
Billet: is rolled from a bloom and square in
dimensions 40mm onside or larger.
8

9. Some of the steel products made in a rolling
mill
9

10. A rolling mill for hot flat
rolling; the steel plate is seen
as the glowing strip
extending diagonally from
the lower left corner
(photo courtesy of
Bethlehem Steel Company)
10

11. Shape Rolling
Work is deformed into a contoured cross
section. Products of shape rolling are I- beams,
U-channels, railroad,bars and rods. Most of the
principles that apply in flat rolling is also
applicable for shape rolling.
Shaping rolls are more complicated several
rolls are used.
Designing the sequence of intermediate
shapes & corresponding roll is called roll pass
design for uniform deformation.
Non uniform reduction result as warping &
cracking
11

12. Various configurations of rolling mills
(a) 2-high rolling mill it can be reverse or no reverse
mills
12

13. Various configurations of rolling mills
(b) 3-high rolling mill
13

14. Various configurations of rolling mills
(c) four-high rolling mill
14

15. (d) cluster mill
Various configurations of rolling mills
15

16. Various configurations of rolling mills
(e) tandem rolling mill
16

17. Thread Rolling
Bulk deformation process used to form threads on cylindrical parts
by rolling them between two dies
 Most important commercial process for mass producing bolts and
screws
 Performed by cold working in thread rolling machines
 Dies used of two types flat dies & round dies
 Advantages over thread cutting (machining):
1. Higher production rates
2. Better material utilization
3. Stronger threads due to work hardening
4. Better fatigue resistance due to compressive stresses
introduced by rolling
17

18. Thread Rolling
Thread rolling with flat dies:
(1) start of cycle, and (2) end of cycle
18

19. Ring Rolling
Deformation process in which a thick-walled ring of
smaller diameter is rolled into a thin walled ring of
larger diameter
 As thick-walled ring is compressed, deformed
metal elongates, causing diameter of ring to be
enlarged
 Hot working process for large rings and cold
working process for smaller rings
 Applications: ball and roller bearing races, steel
tires for railroad wheels, and rings for pipes,
pressure vessels, and rotating machinery
 Advantages: material savings, ideal grain
orientation, strengthening through cold working
19

20. Ring Rolling
Ring rolling used to reduce the wall thickness and
increase the diameter of a ring:
(1) start, and (2) completion of process
20

21. Gear Rolling
Gear rolling is cold working process to
produce gears for automotive industry.
Setup features are like thread rolling
disk or cylindrical blank are oriented
parallel to its axis and at an angle in
case of helical gears.
 Advantages are higher production,
better strength, fatigue strength & less
material waste.
21

22. Roll piercing
 Hot working process for making seamless thick
wall tubes. It utilize two opposing rolls hence
grouped with rolling process.
 When a solid cylindrical part is compressed
high tensile stresses are developed. if
compression is very high internal cracks can be
produced.
 Compressive stresses on cylindrical billet are
applied by two rolls whose axis are oriented at
slight angle 6°.
 A mandrel is used to control size and finish
hole created by action. Rotary tube piercing &
Mannesmann process used for tube making.
22

23. 23

24. Forging
 Deformation process in which work is compressed
between two dies using impact or gradual
pressure.
 Oldest of the metal forming operations, dating
from about 5000 B C
 Components: engine crankshafts, connecting
rods, gears, aircraft structural components, jet
engine turbine parts
 In addition, basic metals industries use forging to
establish basic form of large components that are
subsequently machined to final shape and size
24

25. 25

26. Classification of Forging
Operations
Cold vs. hot forging:
Hot or warm forging – most common, due to
the significant deformation and the need to
reduce strength and increase ductility of work
metal
Cold forging - advantage is increased strength
that results from strain hardening
Impact vs. press forging:
Forge hammer - applies an impact load
Forge press - applies gradual pressure
26

27. Types of Forging Dies
(a) Open- die forging - work is compressed between two flat
dies, allowing metal to flow laterally without constraint
(b) Impression/closed- die forging - die surfaces contain a
cavity or impression that is imparted to work part, thus
constraining metal flow - flash is created
(c) Fleshless forging - work part is completely constrained in die
and no excess flash is produced
27

28. Open- Die Forging
Compression of work part with cylindrical cross-section
between two flat dies
 Similar to compression test
 Deformation operation reduces height and increases
diameter of work
 Common names include upsetting or upset forging
28

29. Impression- Die Forging
Compression of work part by dies with inverse of desired
part shape
 Flash is formed by metal that flows beyond die cavity
into small gap between die plates
 Flash must be later trimmed from part, but it serves an
important function during compression:
 As flash forms, friction resists continued metal flow
into gap, constraining material to fill die cavity
 In hot forging, metal flow is further restricted by
cooling against die plates
29

30. Sequence in impression-die forging:
(1) just prior to initial contact with raw work
piece,
(2) partial compression, and
(3) final die closure, causing flash to form in
gap between die plates
30

31. Impression- Die Forging
Advantages and Limitations
Advantages compared to machining from
solid stock:
Higher production rates
Conservation of metal (less waste)
Greater strength
Favorable grain orientation in the metal
Limitations:
Not capable of close tolerances
Machining often required to achieve accuracies and
features needed, such as holes, threads, and mating
surfaces that fit with other components
31

32. Flash less Forging
Compression of work in punch and die tooling whose
cavity does allow for flash
 Starting work part volume must equal die cavity
volume within very close tolerance
 Process control more demanding than
impression-die forging
 Best suited to part geometries that are simple and
symmetrical
 Often classified as a precision forging process
32

33. Flash less forging:
(1) just before initial contact with work piece,
(2) partial compression, and
(3) final punch and die closure
Coining
It is special application of closed die forgining fine
details in die are impressed on top and bottom of
work part give us good surface finish & accuracy.
33

34. Forging Hammers (Drop
Hammers) Apply an impact load against work part - two types:
 Gravity drop hammers - impact energy from falling weight of a
heavy ram
 Power drop hammers - accelerate the ram by pressurized air
or steam
 Disadvantage: impact energy transmitted through anvil into floor
of building
 Most commonly used for impression-die forging
Diagram
showing details
of a drop
hammer for
impression-die
forging
34

35. Forging Presses
Apply gradual pressure to accomplish
compression operation - types:
Mechanical presses - converts rotation of
drive motor into linear motion of ram
Hydraulic presses - hydraulic piston
actuates ram
Screw presses - screw mechanism drives
ram
35

36. Forging Dies
Proper die design is important principles
and limitations in knoweledge.some
terminologies and guidelines are used to
design a die.
Parting line
Draft
Webs & Ribs
Fillet & Radii
Flash
Figure 19.21 consult from book
36

37. Upsetting & Headings
Upsetting also called upset forging is deformation
operation in which a cylindrical work part dia is
increased and length is reduced. Upsetting used in
fastener industry to make heads on nail & bolts.
Heading is used to denote the operation heading
application indicating various die
configuration(fig.19.23)
Performed as mass production operation
cold,warm,hot on special machines called headers.
Limitation max.length of stock to be forged.
Max.length is 3 times of starting stock upset in blow
otherwise metal will bends or buckle instead of
compressing properly.
37

38. Swaging and Radial Forging
Swaging process& radial process is used to
reduce dia of tube or solid rod.
Swaging is accomplished by means of rotating
dies that hammer a work piece radially inward to
taper.(fig:19.25)
A mandrel is also used to control shape & size
of internal dia of tubular parts.
Radial forging is similar to swaging in its action
against work & used to make similar parts.die
will not rotate around the work piece instead
work is rotated.
38

39. Roll forging
Used to reduce cross section of a cyliderical/rectangle
work piece by passing it through a set of opposing rolls
have grooves matching the desired shape of final
part.(fig19.26)
Roll forging is classified as forging although utilize rolls.
Rolls do not turn continuously but rotate only a portion of
one revolution for desire deformation. Roll forging is
stronger and favorable grain structure s compare to
machine.
Orbital forging: deformation occurs by means of cone
shaped upper die rolling & pressing work part.(fig:19.27)
Work is supported on lower die, die is cone only small area
is compressed. Upper die revolves & area under
compression also revolves. Press load requirement is
reduced.
39

40. Hubbing
Deformation process hardened steel form is pressed
into soft steel block used to make mold cavities for
plastic molding and die casting.(fig:19.28)
The hardened steel form called hub is machined to
geometry of part to be molded. Hydraulic press are
used for hub.
Hubbing followed by annealing to recover strain
hardening.
Advantage is that it is easier to machine positive form
than mating negative cavity.
This advantage is multiple in case of when more than
one cavity are made in one block.
40

41. Isothermal & Hot die forging
Isothermal forging is a term applied to hot forging
in which work part is maintained near or at its starting
elevated temperature during deformation usually by
heating forging dies.
Metal flows more readily & force applied to perform
process is reduced.
Isothermal is more expensive than conventional forging.
Titanium& super alloys are forged. Carried out in
vacuum to avoid rapid oxidation.
Hot die forging in which dies are heated to a
temperature that is somewhat below that of work metal
41

42. Trimming
Trimming is operation to remove flash on
work part in impression die forging.
Trimming is accomplished by shearing
when a punch forces the work through a
cutting die.
Trimming is usually done work part is still
hot separate trimming press are included at
each forging hammer or press
If work part is damaged then trimming is
done by grinding or sawing.
42

43. Extrusion
 Compression forming process in which the work
metal is forced to flow through a die opening to
produce a desired cross-sectional shapes.
 Process is similar to squeezing toothpaste out of
a toothpaste tube.
 In general, extrusion is used to produce long parts
of uniform cross-sections.
Advantages:
 A variety of shapes are possible
 Grain structure & strength properties are
enhanced.
 Fairly close tolerance is possible
 Little or no waste material is created.
43

44. Extrusion products
44

45. 45

46. 46
Direct extrusion
 Also called forward extrusion
 As ram approaches die opening, a small portion
of billet remains that cannot be forced through die
opening.
 This extra portion, called the butt, must be
separated from extruded product by cutting it just
beyond the die exit.
 Starting billet cross section usually round, but
final shape is determined by die opening.

47.  Starting billet is prepared with a hole parallel to
its axis.
 This allows passage of a mandrel attached to
dummy block. Billet is compressed and
material is forced to flow through the clearance
between the mandrel and die opening.
 Semi hollow also extruded in same way.
Indirect Extrusion
 Also called backward extrusion and reverse
extrusion.
 Die is mounted to the end of ram rather than at
opposite side of container. 47
Direct Extrusion of Hollow Cross
Sections

48. 48
(a) Direct extrusion to produce a hollow or semi- hollow cross-section; (b)
hollow and (c) semi- hollow cross- sections .
But friction exist between the work surface & walls of the
container causes substantial increase in ram force required.
In hot extrusion friction problem is solved by presence of
oxide layer on surface of billet.
A dummy block is used smaller than billet dia. So that a
narrow ring of oxides layer left in container leaving free
oxides product.

49.  Also called backward extrusion and reverse extrusion.
 Die is mounted to the end of ram rather than at opposite side
of container.
 Ram penetrates into work metal is forced to flow through
clearance in a direction opposite to motion of ram.
 Billet is not forced to move relative to container. No friction of
container walls and ram force is lower than direct extrusion.
 Limitations of indirect extrusion are imposed by the lower
rigidity of hollow ram and difficulty in supporting extruded
product as it exits die.
 For hollow cross sections Ram is pressed into billet forcing
material to flow around the ram and take a cup shape.
49
Indirect Extrusion

50. 50
Indirect extrusion to produce
(a) a solid cross-section and (b) a hollow
cross-section
There are practical limitation of the extruded part made
by this method. Support of the ram is also a problem as
work length increases.

51. Hot Extrusion
 Hot extrusion: prior heating of billet to above its
recrystallization temperature
 Reduces strength and increases ductility of the
metal, permitting more size reductions and more
complex shapes.
 Advantage include
less force ram,
increased ram speed
 Cooling of billet as contacts with container walls is
a problem isothermal extrusion is used.
 Lubrication is also critical in hot extrusion for certain
metals e.g. steel. To reduce friction.
52

52. Cold extrusion: generally used to produce discrete
parts .The term impact extrusion is used to
indicate high speed cold extrusion.
Advantages :
Strength, close tolerance, surface finish, absence of
oxides layer, high production rate. Cold extrusion
eliminates need for heating billet.
Continues vs. Discrete Processing
A true continuous process operates in steady state
mode give ideal extrusion by producing long
sections in one cycle but limited due to size of billet
better than semi continuous process.
In discrete process a single part is produced in each
cycle. Impact extrusion is example of discrete
processing case. 55
Cold Extrusion

53. Extrusion Ratio
The ratio cross sectional area of starting billet
to final cross sectional area of extruded
section. The term applies for both direct &
indirect extrusion.
Rx=Ao/Af
Shape factor:
The ratio of pressure required to extrude a
cross section of a given shape relative to
extrusion pressure of a round cross section of
same area. Kx=0.98+0.02(Cx/Cc)2.25
56

54. Die Material
 For hot extrusion tool & alloy steels. For cold extrusion die
is made of tool steels & cemented carbides.
 Properties of hot extrusion dies high wear résistance, high
hot harness, high thermal conductivity.
 Properties of hot extrusion dies Carbides are used for high
production, long tool life &good dimensional control.
 Presses may be
 horizontal & vertical but horizontal are more common.
 hydraulic & mechanical driven.
57

55. 58
Horizontal extrusion presses
(15- 50 MN capacity or up to 140
MN)
Vertical extrusion
presses (3- 20 MN
capacity)

56. A complex extruded cross-section for a heat sink
(photo courtesy of Aluminum Company of
America)
59
FFT is it hot or cold extrusion

57. Other Extrusion Processes
Impact extrusion
 High speed,
 shorter strokes
 can be carried out for forward, backward or combination
 Thin walls are possible with impact.
 Large reduction & production rate making it important
at commercial process.
Hydrostatic Extrusion
 Billet container interface friction reduction by surrounding
the billet with fluid inside the container and
pressurizing fluid by ram.
 No friction inside the container so ram force will be lower.
 Carried out at room temperature or at elevated
temperature. Special fluids are used adaptation of direct
extrusion.
60

58. 61

59. Defects in Extruded Products
Centerbrust:defect due to internal crack develops as a
result of tensile stresses along centerline of work part
during extrusion. Difficult to detect it. This defect include
arrowhead fracture, canter cracking & chevron cracking.
Piping: defect associated with direct extrusion, formation
of sink hole in the end of billet. Use of dummy block helps
to avoid piping. Tailpipe & fish tailing is given other names.
Surface cracking: defect occurs due to high work part
temperature that cause crack occurred due to high speed of
extrusion leading high strain rate & heat generation. High
friction & surface chilling of high temperature billets.
62

60. Wire and Bar Drawing
 Cross-section of a bar, rod, or wire is reduced by
pulling it through a die opening.
 Similar to extrusion except work is pulled
through die in drawing (it is pushed through in
extrusion).
 Although drawing applies tensile stress,
compression also plays a significant role since
metal is squeezed as it passes through die opening.
Figure 19.40 - Drawing of bar, rod, or wire
63

61. Wire Drawing vs. Bar Drawing
Difference between bar drawing and wire drawing is stock size
Bar drawing - large diameter bar and rod stock
Wire drawing - small diameter stock - wire sizes down to 0.03 mm
(0.001 in.) are possible
Bar Drawing
 is completed as single draft operation stock is pulled through
die opening.
 Beginning stock has larger dia.
 Limits the length of the work can be drawn meeting a batch
type operation.
Wire Drawing
 is drawn from coils passed through a series of dies.
 Dies varies between 4 to 12.
64

62. Continuous drawing is used for long production achieved with wire
coils can be butt welded each to the next to make the operation
truly continuous.
Area reduction in drawing change in size of the work is given as
r= Ao – Af / Ao
Draft is simply a difference between original & final stock diameters
d=Do- Df .
Drawing practice:
Usually performed as cold working
Most frequently used for round cross-sections
Products:
Wire: electrical wire; wire stock for fences, coat hangers, and
shopping carts
Rod stock for nails, screws, rivets, and springs
Bar stock: metal bars for machining, forging, and other processes6
5

63. Advantages of Drawing
 Close dimensional control
 Good surface finish
 Improve mechanical properties
 Economical mass production
Drawing Equipment
 Bar drawing is accomplished on a machine is called a draw
bench consist of entry table, die stand,carriage,exist rack.
 Carriage is used to pull the stock through draw die
powered by hydraulic cylinders or motor driven.
 Die stand can hold more than one die several bars can be
pulled through respective dies.
66

64. 67
Hydraulically operated draw bench for drawing metal bars

65. Wire Drawing
Continuous drawing machines consisting of multiple draw dies
(typically 4 to 12) separated by accumulating drums
◦ Each drum (capstan) provides proper force to draw wire
stock through upstream die
◦ Each die provides a small reduction, so desired total
reduction is achieved by the series
◦ Annealing sometimes required between dies
Continuous drawing of wire 68

66. Draw Dies
Four regions of the die can be distinguished
 Entry (region usually a bell shaped mouth does
not contact the work)
 Approach angle (drawing processes occurs)
 Bearing surface (land or bearing surface
represents the size of final drawn stock)
 Back relief(the exit zone with an back relief
angle)
 Draw dies are made of tool steels, cemented
carbide and for high speed made of diamond.
69

67. Preparation of the work
 Annealing (to increase ductility)
 Cleaning (to prevent damage of work surface)
 Pointing (reduction in diameter of starting end of
stock so can be inserted through draw die)
Tube Drawing:
Drawing can be used to reduce dia. Or wall
thickness of tubes or pipes produced by extrusion.
Tube can be drawn with and without mandrel(tube
sinking) is applied. Fixed mandrel and floating plug
used.
70

68. Rolling
72

69. Forging
73

70. Extrusion
74

71. BULK DEFORMATION PROCESSES
IN METALWORKING
1. Rolling
2. Forging
3. Extrusion
4. Wire and Bar Drawing
75

72. Wire and Bar Drawing
76

73. 77

74. 78