This document discusses various bulk deformation techniques including forging, rolling, and extrusion. It covers topics like hot working versus cold working, the advantages of each, and specific forging processes like closed-die forging. Forging refines grain structure and improves properties. It describes how grain flow follows the deformation pattern. The document also discusses forging equipment, defects, and provides examples of forging a connecting rod and crankshaft.

1. BULK DEFORMATION
COMPLIED BY
M.BALASUBRAMANIAN

2. Topics for Discussion
• Hot and Cold working
• Forging
• Rolling
• Extrusion
• Wire and Rod Drawing
• Tube Drawing

3. Cold Working:
Plastic deformation of metals below the
recrystallization temperature is known
as cold working. It is generally
performed at room temperature. In
some cases, slightly elevated
temperatures may be used to provide
increased ductility and reduced
strength.

4. Warm Working
• Metal deformation carried out at
temperatures intermediate to hot
and cold forming is called Warm
working .

5. Hot Working
• Plastic deformation of metal carried out at
temperature above the recrystallization
temperature, is called hot working. Under the
action of heat and force, when the atoms of metal
reach a certain higher energy level, the new
crystals start forming. This is called
recrystallization. When this happens, the old
grain structure deformed by previously carried
out mechanical working no longer exist, instead
new crystals which are strain-free are formed.

6. Advantages of Hot Working
• Lower working forces to produce a given shape, which
means the machines involved don't have to be as strong,
which means they can be built more cheaply;
• The possibility of producing a very dramatic shape
change in a single working step, without causing large
amounts of internal stress, cracks
• Sometimes hot working can be combined with a casting
process so that metal is cast and then immediately hot
worked. This saves money because we don't have to
pay for the energy to reheat the metal.
• Hot working can also remove some kinds of defects that
occur in cast metals. It can close gas pockets or voids in
a cast billet; and it may also break up inclusions which

7. The main problems (limitations), however, are
• If the recrystallisation temperature is high, methods are
needed to protect the machines that work the metal.
• The working processes are also dangerous to human operators
and very unpleasant to work near.
• Poor surface finish
• Dimensional change occurs as the worked object cools
• Problem of scale formation on the surface of the hot steel.

8. The Advantages of Cold Working
• A better surface finish may be achieved;
• Dimensional accuracy can be excellent because the work
is not hot so it doesn't shrink on cooling; also the low
temperatures mean the tools such as dies and rollers can
last a long time without wearing out.
• No scale formation.
• Strength and hardness are increased.
• OH & S problems related to working near hot metal are
eliminated.

9. LIMITATIONS
• There is a limit to how much cold work can be
done on a given piece of metal. Accumulation in
the form of piled up dislocations.
• Higher forces are required to produce a given
deformation, which means we need high
capacity machines and cost goes up.

10. Compare Hot & Cold Working
HOT WORKING COLD WORKING
Processing above recrystallization
temp.
Processing below recrystallization
temp.
Low forces required High forces required
New crystals are formed Recrystallization does not occur
No strain hardening Strain hardening takes place
Scale formation No scale formation
No residual stress Considerable residual stress can
occur
Lot of deformation possible Limited deformation.

12. Forging of Metals

13. • Forging is the process by which metal is heated
and is shaped by plastic deformation by suitably
applying compressive force. Usually the
compressive force is in the form of hammer
blows using a power hammer or a press.
• Forging refines the grain structure and improves
physical properties of the metal.
• Grain flow is in the direction of the pattern that
the crystals take during plastic deformation.
Physical properties (such as strength, ductility
and toughness) are much better in a forging than
in the base metal, which has, crystals randomly
oriented.

14. Grain Structure
Fig : A part made by three different procedures, showing grain flow (a) casting (b) machining (c) forging

15. Open-Die Forging
• Is the simplest forging process
• Sizes can very from very small
parts to very large parts
• Open-die forging is carried out
between flat dies or dies of
very simple shape.
• The process is used for mostly
large objects or when the
number of parts produced is
small.
• Open-die forging is often used
to preform the workpiece for
closed-die forging.
•

16. Advantages & Limitations
• Advantages
– Simplest type of forging
– Dies are inexpensive
– Wide range of part sizes
– Good strength
– Generally good for small quantities
• Limitations
– Simple shapes only
– difficult to hold close tolerances
– machining necessary
– low production rate
– poor utilization of material
– high skill required

17. Impression-Die & Closed-Die Forging
• The workpiece acquires the shape of
the die cavities while being forged
between the two shaped dies
• The workpiece is deformed between
two die halves which carry the
impressions of the desired final
shape.
• The workpiece is deformed under
high pressure in a closed cavity.
• Normally used for smaller
components.
• The process provide precision forging
with close dimensional tolerance.
• Closed dies are expensive

18. Advantages & Limitations
• Advantages
– Good utilization of material
– Better properties than Open Die Forgings
– Dies can be made of several pieces and inserts to create
more advanced parts
– Presses can go up to 50,000 ton capacities
– Good dimensional accuracy
– High production rates
– Good reproducibility
• Limitations
– High die cost
– Machining is often necessary
– Economical for large quantities, but not for small quantities

19. FORGING OPERATIONS
• UPSETTING
• EDGING
• FULLERING
• SWAGING
• COINING
• TRIMMING

20. Cross section is increased
and length is decreased

21. • Fullering is a forging operation performed to reduce the
cross section and increase the length by redistributing
the metal to other part. Fullering die cavities are often use
multi cavity impression dies so that the starting bar can
be rough formed before final shaping.
i.e., forging of connecting rod for an internal combustion
engine
• Edging is used to shape the ends of the bars and to gather
metal or in any localized area. The metal flow is confined
in the horizontal direction but it is free to flow laterally to
fill the die.
Fullering

22. Swaging is used to produce a bar with a Smaller
diameter.
• Swaging provides a reduced round cross section
suitable for tapping, threading, upsetting or
other subsequent forming and machining
operations.

23. Coining
• Special application of flashless forging in
which fine detail in the die are impressed
into the top and bottom surfaces of the
workpiece. There is a little flow of metal in
coining.
Examples
Medals, coins, etc

24. Trimming is an operation used to remove flash on
the workpart in impression-die forging. In most
cases, trimming is accomplished by shearing, in
which a punch forces the work through a cutting
die.

25. Other forging operations
• Drawing is used to reduce
the cross-sectional area of
the workpiece with
concurrent increase in
length
• Piercing and punching are
used to produce holes in
metals.
• A scrap is produced in
punching operations but
not in piercing work.

26. TYPES OF FORGING
EQUIPMENTS/MACHINERY
• Smith or Hand forging
• Drop Forging (board and power type)
• Press Forging (mechanical and hydraulic type)
• Roll Forging

27. FORGING MACHINES

29. DROP/BOARD HAMMER
• The upper die and ram are raised by
friction rolls gripping the board.
• After releasing the board, the ram falls
under gravity to produce the blow
energy.
• The hammer can strike between 60-150
blows per minute depending on size and
capacity.
• This is an energy restricted machine. The
blow energy supplied equals the potential
energy due to the weight and the height
of the fall.

30. POWER HAMMER
• Power hammer provides
greater capacity, in which
the ram is accelerated on the
downstroke by steam or air
pressure in addition to
gravity.
• Steam or air pressure is also
used to raise the ram on the
upstroke.
• Types of power hammer
Pneumatic, Steam, motor

31. MECHANICAL PRESS
• Crank press translates rotary motion
into reciprocating linear motion of
the press slide.
• The ram stroke is shorter than in a
hammer or hydraulic press.
• Presses are rated on the basis of the
force developed at the end of the
stroke.
• The blow press is more like squeeze
than like the impact of the hammer,
therefore, dies can be less massive
and die life is longer than with a
hammer.

32. Roll Forging
Roll forging is a deformation process used to reduce the
cross section of a cylindrical (or rectangular) workpiece
by passing it through a set of opposing rolls that have
grooves matching the desired shape of the part. Roll
forging is generally classified as a forging process, even
though it utilizes rolls. The rolls do not turn
continuously in roll forging, but rotate through only a
portion of one revolution corresponding to the desired
deformation to be accomplished on the part.

33. ROLL FORGING

34. FORGING DEFECTS
• Flash line crack, after trimming-
occurs more often in thin
workpieces.
• Cold shut or fold , due to flash or fin
from prior forging steps is forced
into the workpiece. Improper design
• Internal cracking, due to stress.
• Mismatching in forging, because of
mismatched dies
• In-complete die filling
• Buckling, in upsetting forging.
Subject to high compressive stress
• Pitted surface, due to oxide scales
occurring at high temperature stick
on the dies

35. Advantages & Limitations of Forging
Advantages
• Superior mechanical properties
• Close dimensional tolerance
• Forgings can be easily welded
Limitation
• Intricate shapes made by casting is not possible
by forging
• Cost of forging is more because of its
equipment and tooling

36. FORGING A CONNECTING ROD
BLOCKING. A forging operation often used to impart an intermediate shape in
the finishing impression of the dies. Blocking can ensure proper “working” of
the material and contribute to great die life.

38. FORGING A CRANK SHAFT

39. Properties of Die Materials
• Thermal shock resistance
• Thermal fatigue resistance
• High temperature strength
• High wear resistance
• High toughness and ductility
• High hardenability
• High dimensional stability during hardening
• High machinability

40. Raw Material
• Blooms - 150x150 to 320x320 mm
• Billets - 60 x 60 to 110x110
• Slab - 200x1250 to 320x1500
• Blank is the derived product from the above
for various process.(raw material)

41. Manufacture of Bolts
• Shearing
• Heading
• Chamfering
• Threading
• Pickling

42. Manufacture of Nuts
• Shearing (Slugs)
• Heating
• Hot Forging
• Hammering or heading to form
hexagon
• Piercing for hole
• Threading
• Oven for strength

43. Comparison
• Rolling: Compressive deformation process in
which the thickness of a plate is reduced by
squeezing it through two rotating cylindrical
rolls.
• Forging: The workpiece is compressed between
two opposing dies so that the die shapes are
imparted to the work.
• Extrusion: The work material is forced to flow
through a die opening taking its shape. (push)
• Drawing: The diameter of a wire or bar is
reduced by pulling it through a die opening.

44. Rolling of Metals

46. DEFINITION
Flat rolling or Rolling is defined as the
reduction of the cross-sectional area of the
metal stock, or the general shaping of the
metal products, through the use of the rotating
rolls.
Capable of providing high-quality, close
tolerance starting material for various
secondary sheet metal working processes at a
low cost

47. This chapter describes
Flat rolling
 Shape rolling
Production of seamless tubing & pipe
Rolling – process of reducing the thickness of a
long work piece
Plates – having thickness greater than 6mm
Sheets – generally less than 6mm thick
Introduction

48. Flat Rolling
Many hot working processes and other processes that occur at high
temperatures leave a discoloring oxide layer or scale on the surface.
In order to remove the scale the workpiece is dipped into hydrochloric
or sulfuric acid

49. Flat-Rolling Practice
• Hot rolling
– The initial break down of an ingot
– Continuously cast slab
– Structure may be brittle
– Converts the cast structure to a wrought structure
• Finer grains
• Enhanced ductility
– Reduction in defects
• Billets – smaller than blooms and rolled into bars and rods
• Cold rolling
– carried out at room temperature
– Produces sheet and strip metal
– Better surface finish – less scale

50. Flat-Rolling Practice Con’t
Changes in grain structure during hot-rolling

51. Defects in Rolled Plates & Sheets
• Wavy edges (a) – result of roll bending
• Zipper cracks (b) - Due to low ductility of the material
• Edge Cracks (c) - Due to low ductility of the material
and barelling
• Alligatoring (d) - Occurs in nose and tail of the slab due
to inhomogenity of the material

52. Shape-Rolling Operations
• Various shapes can be produced by shape rolling
– Bars
– Channels
– I-beams
– Railroad rails
• Roll-pass design requires considerable experience in order
to avoid external and internal defects

54. Ring Rolling
• A thick ring is expanded into a large diameter ring
– The ring is placed between the two rolls
– One of which is driven
– The thickness is reduced by bringing the rolls together
• The ring shaped blank my be produced by
– Cutting from plate
– Piercing
– Cutting from a thick walled pipe
• Typical applications of ring rolling:
– Large rings for rockets
– Gearwheel rims
– Ball-bearing and roller-bearing races

55. RING ROLLING
(a) Schematic illustration of Ring-
rolling operation. Thickness
reduction results in an increase in
the part diameter.
Powder Rolling

56. Thread Rolling
• Cold-forming process
• Straight or tapered threads are formed on round rods by passing the pipe
though dies
• Typical products include Screws and Bolts
• Threads are rolled in the soft condition
• Threads may then be heat treated, and subjected to final machining or
grinding
• Uncommon or special-purpose threads are machined

57. ROLLING MILL
Various configurations of rolling mills:
(a) two high, (b) three high, (c) four high,
(d) cluster mill, and (e) tandem rolling mill.

58. Cluster Mill
Planetary Mill

59. • The basic rolling mill consists of two opposite
rotating rolls, referred as a two-high rolling
mill. In the three-high rolling mill, there are
three rolls in a vertical column. To achieve a
series of reductions, the work can be a passed
through from either side by raising or lowering
the strip after each pass.
• Roll-work contact length is reduced with a
lower roll radius, and this leads to lower
forces, torque, and power. The four-high
rolling mill uses two smaller diameter rolls to
contact the work and two backing rolls behind
them.

60. SKEW ROLLING
Similar to roll
forging, used for
making ball
bearings. Rod
stock is fed in to
the roll gap and
spherical blanks
are formed
continuously by
the rotating rolls.

61. Production of Seamless Pipe & Tubing
• Rotary tube piercing (Mannesmann process)
– Hot-working process
– Produces long thick-walled seamless pipe
– Carried out by using an arrangement of rotating rolls
• Tensile stresses develop at the center of the bar when it is subjected to compressive forces

62. ROLL PASS DESIGN
Long products are normally rolled in several passes, whose numbers are determined by the
ratio of the initial input steel material (square or round billet or bloom) and final cross
section of finished product. The cross section area is reduced in each pass and form and size
of the steel material being rolled gradually approach to the desired profile.
Rolling is carried out between grooved rolls. Two opposite grooves in the collaborating
rolls form a pass, which corresponds to a work piece’s cross section shape expected after
the pass. After every pass, the cross section decreases and its shape becomes closer to a
shape of the final product. Development of subsequent pass shapes and its proper location
on the rolls is called the roll pass design. Roll pass design generally means the cutting of
grooves in the roll body through which steel to be rolled is made to pass sequentially to
get the desired contour and size.

64. EXTRUSION

65. Extrusion
A compression forming process in which the work metal is forced
to flow through a die opening to produce a desired cross-
sectional shape. The cross section varies from solid, round,
rectangular, L-shape, T-shape, I-section, hollow section, etc.
Raw material is forced through a die at a speed of 5 to 50m/min
and to a length of 25 to 40m.
Extrusion pressure is the force divided by the CSA of the billet.
At the initial stage the extrusion pressure rises rapidly due to
initial compression on the billet that fills the container.
In direct extrusion, at maximum pressure the metal starts to flow
and the pressure required decreases with decreasing length of
the billet. In in-direct extrusion, since there is no relative
motion between the billet and the container wall, the pressure
required is almost constant. At the end again the pressure rises
rapidly, because the metal starts to flow in perpendicular
direction to the direction of the applied force.

66. Ram Force
Variation of Ram Force with ram
stroke and die angle.

67. STANDARD EXTRUSIONS

68. Advantages
– variety of sections possible (hot extrusion)
– grain structure and strength enhancement (cold)
– close tolerance (cold)
– no material wastage.
– Improved Surface finish

69. Classification of Extrusion Processes
There are several ways to classify metal extrusion processes;
By direction
• Direct / Indirect extrusion
• Forward / backward extrusion
By operating temperature
• Hot / cold extrusion
By equipment
• Horizontal and vertical extrusion

70. Extrusion Processes
Hot extrusion
Processing temperature to above the re-crystalline
temperature.
Reduction in ram force & increase in the ram speed
Controlling the cooling rate is a problem.
Cold extrusion
Processing temperature below the re-crystalline
temperature
Increased strength due to strain hardening
close tolerances, improved surface finish, absence
of oxide layer and high production rates.

71. Types of Extrusion
Direct Extrusion
The ram forces the work billet metal to move
forward to pass through the die opening.
Indirect Extrusion
The die is mounted to the ram rather than at the
opposite end of the extruder container housing.

72. Direct Extrusion
The metal billet is placed in a
container and driven through
the die by the ram.

73. Indirect Extrusion
• The hollow ram
containing the die is kept
stationary and the
container with the billet
is caused to move.
• The material is forced to
flow through a die in a
direction opposite to
ram’s motion.

74. Forward and Backward Extrusion
Forward Extrusion
•Metal is forced to flow in the same
direction as the punch.
• The punch closely fits the die cavity to
prevent backward flow of the material.
Backward Extrusion
• Metal is forced to flow in the direction
opposite to the punch movement.
• Metal can also be forced to flow into
recesses in the punch.

75. Hydrostatic Extrusion
Hydrostatic extrusion is a form of impact extrusion, uses
a fluid hydrostatic pressure instead of a mechanical ram.
This is useful for making parts out of materials such as
Molybdenum, Tungsten that are relatively hard to extrude
using normal extrusion methods.
Using hydrostatic system to reduce the friction and lower
the power requirement. Sealing is the major problem.

76. Lateral Extrusion

77. Extrusion Temperature Ranges for
Various Metals
C
Lead 200–250
Aluminum and its alloys 375–475
Copper and its alloys 650–975
Steels 875–1300

78. Impact Extrusion
Impact extrusion is performed at higher speeds and
shorter strokes than conventional extrusion.
For making thin wall-thickness items by permitting
large deformation at high speed.
It is commonly used to make collapsible tubes such
as toothpaste tubes, cans usually using soft materials
such as aluminum, lead, tin.

79. Figure 15.14 Schematic illustration of the impact-extrusion process. The extruded parts are stripped by
the use of a stripper plate, because they tend to stick to the punch.
Impact Extrusion

80. Extrusion Defects
a) Centre-burst: internal crack due to excessive tensile stress at
the centre possibly because of high die angle.
b) Piping: sink hole at the end of billet under direct extrusion.
c) Surface cracking: High part temperature due to low extrusion
speed and high strain rates.

81. Factors Influencing the Forces
• Friction
• Material Properties
• Reduction in Area
• Speed
• Temperature
• Geometry of the Die

82. WIRE
DRAWING

83. WIRE DRAWING

84. Principle of Rod/Wire Drawing
• Drawing operation involves pulling of a
metal through a die by applying a tensile
force from outer side of the die. Most of the
plastic flow is caused by compression force
that arises from the reaction of the metal with
the die.
• Reduction in diameter of a solid bar by
successive drawing is shown as bar, rod or
wire depending upon the diameter of the final
product.
• When a hollow tube is drawn with a mandrel,
it is called as tube drawing.

85. • The rod is cold drawn through a carbide die of a
smaller diameter and recoiled. The cold drawn rod is
now smaller in diameter, longer in length, brighter in
appearance, higher in tensile strength and called
WIRE. Our wire is then sent on to be straightened
and cut to length or formed directly from the coil.
Wire Drawing Benefits:
• Manufacturing wire from rod to a specific size
diameter
• Improving the finished surface and removing scale
from the rod
• Improving tensile strength in the finished material
• Providing more consistent round shape of the
material.

86. Die Materials Overview
• Tungsten Carbide:
– Lowest cost, shock resistance, ease of production, large sizes available.
– Lower life expectancy.
• Natural Diamonds:
– Wear resistance, gives excellent wire surface, high thermal conductivity,
longer life expectancy
– Susceptible to fractures from shock or wear, limited availability in
required high quality and quantity, constantly escalating price.
• Synthetic Single Crystal:
– high thermal conductivity, predictable wear schedule, uniform wear
pattern gives longer life expectancy.
• Polycrystalline Diamond:
– Excels in life expectancy, wear resistance of diamond, shock resistance
of carbide, high availability, cost effectiveness

87. Tube Drawing
Tube drawing is also similar to wire drawing,
except that a mandrel of appropriate diameter
is required to form the internal hole.
• Here two arrangements are shown in figure
(a) with a floating plug and
(b) with a moving mandrel
• The process reduces the diameter and
thickness of the tube.

88. Drawing Equipment

89. THE END