The document discusses various bulk metal forming processes including forging, rolling, extrusion, and drawing. It provides classifications and examples of forging types like open die and closed die forging. Rolling processes are categorized by geometry like flat or shape rolling and temperature like hot or cold rolling. Extrusion can be direct or indirect and produces parts with uniform cross-sections. Drawing reduces the diameter of wires or bars by pulling them through a die. These bulk forming methods involve compressive and tensile forces to plastically deform metals into net or near-net shapes.

1. SRI RAMAKRISHNA INSTITUTE OF TECHNOLOGY,
COIMBATORE-10
An Autonomous Institution
(Approved by AICTE, New Delhi – Affiliated to Anna University, Chennai)
Manufacturing processes- UMECOO2
I.Karthikeyan
Assistant Professor,
Mechanical Department .
6/10/2021 1

2. FORGING
Forging - defined as metal working
process by which metals and alloys
are plastically deformed to the
desired shapes by the application
of compressive forces.
Classification:
 Open Die Forging
 Impression / closed die forging
2

3. Metal Forming
• (a) Ideal deformation of
a solid cylindrical
specimen compressed
between flat frictionless
dies.
• (b) Deformation in
upsetting with friction at
the die-workpiece
interfaces.
Open-Die Forging
3

4. Metal Forming
Impression (Closed) Die Forging
• Schematic illustration of stages in impression-die forging. Note
the formation of flash, or excess material that is subsequently
trimmed off.
4

5. Metal Forming
Load-Stroke Curve in Closed-Die Forging
• Typical load-stroke
curve for closed-die
forging. Note the
sharp increase in load
after the flash begins
to form. In hot-forging
operations, the flash
requires high levels of
stress, because it is
thin-that is, it has a
small h-and cooler
than the bulk of the
forging.
5

6. Metal Forming
Heading
• Forging heads on
fasteners such as bolts
and rivets. These
processes are called
heading.
Piercing Operations
• Examples of piercing
operations.
6

7. Metal Forming
Cogging Operation
• Schematic illustration of a cogging operation on a rectangular
bar. With simple tools, the thickness and cross-section of a bar
can be reduced by multiple cogging operations. Note the
barreling after cogging. Blacksmiths use a similar procedure to
reduce the thickness of parts in small increments by heating the
workpiece and hammering it numerous times.
7

8. Metal Forming
Forging A Connecting Rod
• Stages in forging a connecting rod for an internal combustion
engine. Note the amount of flash that is necessary to fill the die
cavities properly.
8

9. Metal Forming
Features Of A Forging Die
Hot-Forging Temperature Ranges
Metal °C Metal °C
Aluminum alloys
Copper alloys
Nickel alloys
400-450
625-950
870-1230
Alloy steels
Titanium alloys
Refractory alloys
925-1260
750-795
975-1650
9

10. Metal Forming
Presses Used In Metalworking
• Schematic illustration of various types of presses used in
metalworking. The choice of the press is an important factor in
the overall operation.
10

11. Metal Forming
Flat-And-Shape-
Rolling Processes
11

12. Metal Forming
Flat-Rolling Process
• Schematic illustration of the
flat-rolling process. A greater
volume of metal is formed by
rolling than by any other
metalworking process.
• Relative velocity distribution
between roll and strip surfaces.
Note the difference in the
direction of frictional forces. The
arrows represent the frictional
forces acting on the strip.
12

13. Metal Forming
Roll Bending and Workpiece Spreading
• (a) Bending of straight
cylindrical rolls because of the
roll force. (b) Bending of rolls,
ground with camber, that
produce a sheet of uniform
thickness during rolling.
•Increase in the width of a
strip (spreading) in flat
rolling.
13

14. Metal Forming
Defects In Flat Rolling
• Schematic illustration of typical defects in flat rolling: (a) wavy
edges; (b) zipper cracks in the center of strip; (c) edge cracks;
(d) alligatoring.
14

15. Metal Forming
Shape Rolling
• Stages in shape
rolling of an H-
section part.
Various other
structural
sections, such
as channels and
I-beams, are
also rolled by
this process.
15

16. Metal Forming
Ring-Rolling
• (a) Schematic illustration of a ring-rolling operation. Reducing
the thickness results in an increase in the part’s diameter. (b)
Examples of cross-sections that can be formed by ring rolling.
16

17. Metal Forming
Types Of Extrusion
• Types of
extrusion.
(a) direct;
(b) indirect;
(c) hydrostatic;
(d) impact.
17

18. Metal Forming
Extrusion
• Extrusion and examples
of products made by
sectioning off extrusions.
• Schematic illustration of three
different types of metal flow in
direct extrusion.
18

19. Metal Forming
Chevron Cracking
• (a) Deformation zone in extrusion, showing rigid and plastic
zones. Note that the plastic zones do not meet, leading to
chevron cracking. The same observations are also made in
drawing round bars through conical dies and drawing flat sheet
plate through wedge-shaped dies. (b) Chevron cracking in round
steel bars during extrusion. Unless the part is inspected
properly, such internal detects may remain undetected and
possibly cause failure of the part in service.
19

20. Metal Forming
Drawing
• Variables in drawing
round rod or wire.
• Variation in strain and flow stress
in the deformation zone in drawing.
Note that the strain increases
rapidly toward the exit. The reason
is that when the exit diameter is
zero, the true strain reaches infinity.
The point Ywire represents the yield
stress of the wire.
20

21. Metal Forming
Forming Processes For Rocket Casings
• The forming processes involves in the manufacture of solid
rocket casings for the U.S. Space Shuttle.
21

22. 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: cylindrical bars and billets,
rectangular billets and slabs, and similar
shapes
• These processes work by stressing metal
sufficiently to cause plastic flow into desired
shape
• Performed as cold, warm, and hot working
operations
22

23. Why do we use bulk processes?
• Produces common shapes inexpensively
• Good mechanical properties
23

24. Common shapes
24

25. Basic principle
25
v, F
Reduction in
size
• Push or pull
• Single shot or
continuous
• Hot or cold
• Malleable material
• Refine and redirect the
grain
• Alters geometry
• Alters material property

26. Importance of Bulk Deformation
• 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
26

27. Four Basic Bulk Deformation
Processes
1. Rolling – slab or plate is squeezed
between opposing rolls
2. Forging – work is squeezed and shaped
between 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
27

28. Rolling
Rolling process in which work thickness is
reduced by compressive forces exerted by two
opposing rolls
28
Figure 19.1 - The rolling process (specifically, flat rolling)

29. The Rolls
The rotating rolls perform two main
functions:
• Pull the work into the gap between them
by friction between workpart and rolls
• Simultaneously squeeze the work to
reduce cross section
29

30. 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
30

31. Figure 3 - Some of the steel products made in a rolling mill
31

32. Figure 4 - Side view of flat rolling, indicating before and after
thicknesses, work velocities, angle of contact with rolls, and
other features
32

33. Flat Rolling – Terminology
Draft = amount of thickness reduction
33
f
o t
t
d 

where d = draft; to = starting thickness; and tf = final thickness

34. Flat Rolling – Terminology
Reduction = draft expressed as a fraction of
starting stock thickness:
34
o
t
d
r 
where r = reduction

35. Shape Rolling
Work is deformed into a contoured
cross-section rather than flat (rectangular)
• Accomplished by passing work through
rolls that have the reverse of desired
shape
• Products include:
– Construction shapes such as I-beams,
L-beams, and U-channels
– Rails for railroad tracks
– Round and square bars and rods
35

36. Figure 19.5 - 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)
36

37. Rolling Mills
• Equipment is massive and expensive
• Rolling mill configurations:
– Two-high – two opposing large diameter rolls
– Three-high – work passes through both
directions
– Four-high – backing rolls support smaller work
rolls
– Cluster mill – multiple backing rolls on smaller
rolls
– Tandem rolling mill – sequence of two-high
mills 37

38. Figure 5 - Various configurations of rolling mills:
(a) 2-high rolling mill
38

39. Figure .6 - Various configurations of rolling mills:
(b) 3-high rolling mill
39

40. Figure 7 - Various configurations of rolling mills:
(c) four-high rolling mill
40

41. Cluster Mill
Multiple backing rolls allow even smaller roll
diameters
41
Figure 8 - Various configurations of rolling mills: (d) cluster mill

42. Tandem Rolling Mill
A series of rolling stands in sequence
42
Figure 9 - Various configurations of rolling mills:
(e) tandem rolling mill

43. 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
• Advantages over thread cutting (machining):
– Higher production rates
– Better material utilization
– Stronger threads due to work hardening
– Better fatigue resistance due to compressive
stresses introduced by rolling
43

44. Figure 10 - Thread rolling with flat dies:
(1) start of cycle, and (2) end of cycle
44

45. 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
45

46. Figure 11 - Ring rolling used to reduce the wall thickness and
increase the diameter of a ring:
(1) start, and (2) completion of process
46

47. Swaging
Accomplished by rotating dies that
hammer a workpiece radially inward to
taper it as the piece is fed into the dies
• Used to reduce diameter of tube or solid
rod stock
• Mandrel sometimes required to control
shape and size of internal diameter of
tubular parts
47

48. Figure 12 - Swaging process to reduce solid rod stock; the dies
rotate as they hammer the work In radial forging, the workpiece
rotates while the dies remain in a fixed orientation as they
hammer the work
48

49. Trimming
Cutting operation to remove flash from
workpart in impression-die forging
• Usually done while work is still hot, so a
separate trimming press is included at the
forging station
• Trimming can also be done by alternative
methods, such as grinding or sawing
49

50. Figure 13 - Trimming operation (shearing process) to remove the flash
after impression-die forging
50

51. Extrusion
Compression forming process in which the
work metal is forced to flow through a die
opening to produce a desired cross-sectional
shape
• Process is similar to squeezing toothpaste
out of a toothpaste tube
• In general, extrusion is used to produce long
parts of uniform cross-sections
• Two basic types of extrusion:
– Direct extrusion
– Indirect extrusion
51

52. Figure 14 - Direct extrusion
52

53. Comments on 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
53

54. Figure 15 - (a) Direct extrusion to produce a hollow or semi-hollow
cross-section; (b) hollow and (c) semi-hollow cross- sections
54

55. Figure 16 - Indirect extrusion to produce
(a) a solid cross-section and (b) a hollow cross-section
55

56. Comments on Indirect Extrusion
• Also called backward extrusion and
reverse extrusion
• Limitations of indirect extrusion are
imposed by the lower rigidity of hollow ram
and difficulty in supporting extruded
product as it exits die
56

57. General Advantages of
Extrusion
• Variety of shapes possible, especially in hot
extrusion
– Limitation: part cross-section must be uniform
throughout length
• Grain structure and strength enhanced in
cold and warm extrusion
• Close tolerances possible, especially in cold
extrusion
• In some operations, little or no waste of
material 57

58. Hot vs. Cold Extrusion
• Hot extrusion - prior heating of billet to
above its recrystallization temperature
– This reduces strength and increases ductility
of the metal, permitting more size reductions
and more complex shapes
• Cold extrusion - generally used to produce
discrete parts
– The term impact extrusion is used to indicate
high speed cold extrusion
58

59. Extrusion Ratio
Also called the reduction ratio, it is defined
as
where rx = extrusion ratio; Ao = cross-
sectional area of the starting billet; and Af
= final cross-sectional area of the extruded
section 59
f
o
x
A
A
r 

60. Figure 17
(a) Definition of die angle in direct extrusion;
(b) effect of die angle on ram force
60

61. Comments on Die Angle
• Low die angle - surface area is large,
leading to increased friction at die-billet
interface
– Higher friction results in larger ram force
• Large die angle - more turbulence in metal
flow during reduction
– Turbulence increases ram force required
• Optimum angle depends on work material,
billet temperature, and lubrication
61

62. Comments on Orifice Shape
of Extrusion Die
• Simplest cross section shape = circular die
orifice
• Shape of die orifice affects ram pressure
• As cross-section becomes more complex,
higher pressure and greater force are
required
62

63. Figure 18 - A complex extruded cross-section for a heat sink (photo
courtesy of Aluminum Company of America)
63

64. Extrusion Presses
• Either horizontal or vertical
– Horizontal more common
• Extrusion presses - usually hydraulically
driven, which is especially suited to
semi-continuous direct extrusion of long
sections
• Mechanical drives - often used for cold
extrusion of individual parts
64

65. 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
65

66. Figure 19 - Drawing of bar, rod, or wire
66

67. Area Reduction in Drawing
Change in size of work is usually given by
area reduction:
where r = area reduction in drawing; Ao =
original area of work; and Ar = final work
67
o
f
o
A
A
A
r



68. 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
• Although the mechanics are the same, the
methods, equipment, and even
terminology are different 68

69. Drawing Practice and Products
• 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 processes
69

70. Bar Drawing
• Accomplished as a single-draft
operation - the stock is pulled through one
die opening
• Beginning stock has large diameter and is
a straight cylinder
• This necessitates a batch type operation
70

71. Figure 20 - Hydraulically operated draw bench
for drawing metal bars
71

72. 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
72

73. Figure 21 - Continuous drawing of wire
73

74. The End
74