It explains about the hot and cold working process

1. METAL FORMING PROCESS
BY
ARAVINDKUMAR B
1

2. BULK DEFORMATION PROCESSES:
 Metal forming operations which cause significant shape
change by deformation in metal parts whose initial form
is bulk rather than sheet.
 These processes work by stressing metal sufficiently to
cause plastic flow into desired shape.
 Performed as cold, warm, and hot working operations.
 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 2

3. METAL FORMING:
 It refers to changing the shape of materials by
mechanical without addition or deletion of materials in
solid or semi-solid condition.
 It reduces the internal cavities or voids present.
 These processes are used to achieve optimum
mechanical properties in the metal.
 These processes are to convert raw materials to the
required useful shapes.
 Applications: Aluminium/Steel frame of doors and
windows, coins, springs, elevator doors, cables, wires.
 Examples: Forging, Rolling, Extrusion, Drawing.
3

4. HOT WORKING OF METALS:
o Mechanical working of a metal above the
recrystallization temperature but below the melting point
is known as hot working.
o Normally, the recrystallization temperature of metal will
be about 30 to 40 % of its melting temperature.
RECRYSTALLIZATION TEMPERATURE:
o It is defined by American Society of Metals: “ the
approximate minimum temperature at which
complete recrystallization of a cold worked metal
occurs within a specified time “.
o Normally, the recrystallization temperature will range
from 0.4 Tm to o.5 Tm.
o Where, Tm = Melting point of the metal in absolute
scale.
4

5. Advantages of Hot Working:
o Force requirement is less when compared to cold working
process for making the required shape.
o It is quick and economical process.
o Porosity is eliminated and density of the metal is
increased.
o This process is very suitable for all metals.
o As grain structure is refined, toughness, ductility, and
resistance can be improved.
Disadvantages of Hot Working:
o Tooling and handling cost are high.
o Surface finish may be poor due to oxidation and scaling.
o Sheets and wires cannot be produced.
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6. TYPES OF HOT WORKING PROCESSES:
 Hot Forging
a) Hammer Forging
b) Drop Forging
c) Upset Forging
d) Press Forging
e) Roll Forging
 Hot Rolling
 Hot Extrusion
 Drawing
 Swaging
 Hot Spinning 6

7. COLD WORKING OF METALS:
o Mechanical working of a metal below the recrystallization
temperature is known as cold working.
o The recrystallization temperature is about one half of the
absolute melting temperature but generally cold working
is carried out only at room temperature.
Materials Used for Cold Working:
 Low and Medium Carbon Steel
 Copper and Light Alloys
 Materials like Al, Mg, Titanium
7

8. Advantages of Cold Working:
o Better surface finish is being obtained.
o This process provides higher dimensional accuracy
o Widely applied as a forming process for steel.
o Thin material can be obtained.
o More suitable for mass production.
Disadvantages of Cold Working:
o Close tolerances cannot be achieved.
o Brittle materials cannot be cold worked.
o Stress formation in the metal during cold working is
higher.
o Heavy force is required to accomplish deformation of the
material.
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9. TYPES OF COLD WORKING PROCESSES:
 Drawing
a) Blank Drawing b) Wire Drawing
c) Tube Drawing d) Metal Spinning
e) Embossing
 Squeezing
a) Coining b) Sizing c) Swaging
d) Knurling e) Extrusion
 Bending
a) Plate Bending
b) Angle Bending
c) Roll Forming
d) Seaming 9

10. COMPARISON BETWEEN HOT & COLD WORKING:
S. No. HOT WORKING COLD WORKING
1 Working above
recrystallization temperature
Working below recrystallization
temperature
2 New crystal are formed after
hot working
No recrystallization
3 Harden the metal No hardening
4 Impurities are removed from
the metal
Impurities are not removed
5 Large size metals also
deformed
Limited to size
6 Surface finish is not good Good surface finish can be
obtained
7 Elongation of metal takes
place
Elongation decreases
8 Internal stress is not formed Stress formation in the metal
will occur
10

11. HOT AND COLD WORKING:
11

12. FORGING:
 In this process, the desired shape is obtained by the
application of a compressive force.
 In hot forging, the metal is heated above the
recrystallization temperature.
 Then it is compressed and squeezed to the required shape
by using hammer or press tool.
TYPES OF FORGING:
 Smith or Open Die Forging
a) Hand Forging b) Power Forging
 Impression or Closed Die Forging
a) Drop Forging b) Press Forging c) Upset Forging
 Roll Forging
12

13.  SMITH OR OPEN DIE FORGING:
o In this process, the forging is done in a heated work at
the proper temperature by placing on flat surface of anvil
through hammering the metal piece.
 Deformation operation reduces height and increases
diameter of work.
13

14. o Heavy forgings weighing up to 25,000kg are produced.
o This forging is very simple and flexible.
o Much useful for producing simple shapes like U bolts,
Chisels, Rectangular, Circular, Hexagonal shapes.
a) HAND FORGING:
o The metal is heated and placed over the anvil by using
tongs.
o One side of the former is held on the parts to be forged
while the other side is struck with a sledge by a helper.
o Repeated blows are given by a sledge hammer to obtain
the metal into required shape.
14

15. b) POWER FORGING:
o In forging, power hammer or power presses are used.
o Machines, which work on forging by blow are called
hammers where as those working by pressure are called
presses.
o In power hammer, a suddenly falling weight which
strikes on the metal makes into required shape.
o In power press, the compressive force is used to shape
the metal.
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16.  ADVANDAGES & DISADVANTAGES SMITH OR
OPEN DIE FORGING :
Advantages
 Simple, inexpensive dies;
 Wide range of sizes;
 Good strength
Limitations
 Simple shapes only;
 Difficult to hold close tolerances;
 Machining necessary;
 Low production rate;
 Poor utilization of material;
 High skill required
16

17.  IMPRESSION OR CLOSED DIE FORGING:
o In this process, the forging is done by squeezing the
work piece between two shaped and closed dies.
17

18. a) DROP FORGING:
o In this, impression dies called closed dies are used.
o The upper die is fitted on the ram and the lower die is
fitted on the anvil.
o Both the dies have impressions.
o Two rollers are fixed on the board when the rolls rotate
opposite to each other.
o It drives the board upward and lifting the ram.
o When the rolls are released, the ram will falls down and
producing a working stroke.
o A single blow of press makes small and simple parts and
large complicate shapes are made by no. of steps.
o Applications: Spanner, Automobile & Machine parts.
18

19. b) PRESS FORGING:
o It is done by a press. The press may be operated either
mechanically or hydraulically.
o The action is relatively slow squeezing rather than
delivering heavy blows.
o There is anvil to fix the lower die and the upper die is
fitted fix in the ram.
o The ram is allowed to move down slowly and presses the
metal slowly with high pressure.
o The finished component may be automatically removed
by providing ejectors in the die set.
o The capacity range from 50 x 10³ to 80 x 10^5 kg and
speeds vary from 34 to 40 strokes per minute.
o Applications: Spanner, Connecting Rod, Machine
Components
19

20. c) UPSET FORGING:
 Upset forging increases the diameter of the work piece by
compressing its length.
o It is process of increasing the cross sectional area of the
bar at the expense of its height.
o It is used to form head of bolt and rivet or pins.
o The head may be square, hexagonal or hemispherical.
o The machine is having a die set.
o The die set consists of a fixed die and movable punch.
o The heated metal bar is held inside the solid die and the
force is given to the punch.
o So, the punch will squeeze the heated metal to the shape
of the die cavity.
20

21.  ADVANDAGES & DISADVANTAGES
IMPRESSION OR CLOSED DIE FORGING :
Advantages
 Good utilization of material;
 Better properties than open die forging;
 Good dimensional accuracy;
 High production rate;
 Good reproducibility
Limitations
 High die cost for small quantities;
 Machining often necessary
21

22.  ROLL FORGING:
o Roll forging is a process where round or flat bar stock is
reduced in thickness and increased in length.
o In this process, heated metal bar is passed between the
two rolls. Roll forging is performed by an impression die
forging operation.
o A piece of heated stock is passed between the two rolls.
As the rolls rotate, the heated metal is squeezed.
22

23. FORGING OPERATIONS:
* Upsetting * Punching
* Fullering * Drawing Down
* Bending * Setting Down
* Welding * Cutting
* Trimming * Coining
* Ironing * Blocking
* Cold Forging * Extrusion
* Swaging 23

24.  SWAGING
Process that reduces/increases the diameter, tapers, rods
or points round bars or tubes by external hammering.
 Mandrel sometimes required to control shape and size of
internal diameter of tubular parts
24

25.  COLD FORGING
Process in which slugs of material are squeezed into
shaped die cavities to produce finished parts of precise
shape and size.
25

26.  EXTRUSION
Process which is commonly used to make collapsible
tubes such as toothpaste tubes, cans usually using soft
materials such as aluminum, lead, tin. Usually a small
shot of solid material is placed in the die and is impacted
by a ram, which causes cold flow in the material.
26

27.  FORWARD EXTRUSION
Forward extrusion reduces slug diameter and increases its
length to produce parts such as stepped shafts and
cylinders.
 BACKWARD EXTRUSION
In backward extrusion, the steel flows back and around
the descending punch to form cup-shaped pieces.
27

28.  UPSETTING OR HEADING
Upsetting, or heading, a common technique for making
fasteners, gathers steel in the head and other sections
along the length of the part.
 Product examples: Bolts, Nails, Engine valves
28

29. IRONING
 Ironing is the process of smoothing and thinning the
wall of a shell or cup (cold or hot) by forcing the shell
through a die with a punch.
29

30. COINING
 In sheet metal working, coining is used to form
indentations in the part. It uses dies to press fine detail
into both sides of the work piece.
 It is widely used for lettering on sheet metal or
components such as coins.
30

31. TRIMMING:
 Cutting operation to remove flash from work part in
impression die forging
 Usually done while work is still hot, so a separate
trimming press is included at the forging station
31

32. TOOLS USED IN FORGING :
32

33. TOOLS USED IN FORGING :
33

34. FORGING 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
34

35. FORGING HAMMERS:
35

36. 36

37. AIR AND STEAM HAMMER:
37

38. 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. (See next slide)
 SCREW PRESSES - screw mechanism drives ram
38

39. 39

40. FORGING PRESSES:
40

41. FORGING DEFECTS:
41

42. ROLLING:
 Deformation process in which work thickness is reduced
by compressive forces exerted by two opposing rolls.
 The metal is squeezed between two hard rollers effecting
change in thickness and the length is increased, since
volume is conserved.
42

43. ROLLS:
The rotating rolls perform two main functions:
 Pull the work into the gap between them by friction
between work-part and rolls
 Simultaneously squeeze the work to reduce cross section
ROLLING MILLS:
 A rolling mill consists basically of rolls, bearings,
housing for containing these parts and a drive for
applying power to the rolls and controlling their speed.
 Rolls are made of Cast Steel with or without alloys.
 Finishing rolls are made of Chilled Cast Iron.
 Various arrangement of rolls in the rolling mill
depending on the application.
43

44. ROLLING MILLS:
TWO HIGH ROLLING MILL
THREE HIGH ROLLING MILL 44

45. ROLLING MILLS:
FOUR HIGH ROLLING MILL
CLUSTER MILL
TANDEM ROLLING MILL
45

46. Some of the steel products made in a rolling mill:
46

47. 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 – Metal is rolled at a temperature
above its recrystallization temperature. Higher
reduction in the cross-section is achieved.
• COLD ROLLING – Metal is rolled at a temperature
below its recrystallization temperature. Better strength
and control of dimensions are achieved 47

48. FLAT (STRIP) ROLLING:
 It utilizes a series of rolls to gradually change the shape of
the metal.
 As the fast moving continuous strip passes between the
rolls, the cross-sectional shape is changed to the desired
form.
48

49. SHAPE ROLLING:
 Various shapes can be produced by shape rolling.
 Straight and long structural shapes such as solid bars
with various cross-sections, channels, I-beams, railroad
rails are rolled by passing the stock through a set of
specially designed rolls.
 Rolling mills can use a variety of roller shapes to get
different cross-sections of the rolled bars.
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50. SHAPE ROLLING:
50

51. 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
51

52. THREAD ROLLING:
Thread rolling with flat dies:
(1) start of cycle (2) end of cycle
52

53. 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
53

54. RING ROLLING:
Ring rolling used to reduce the wall thickness and
increase the diameter of a ring:
(1) Start (2) completion of process
54

55. ROLLING DEFECTS:
(a) wavy edges; (b) zipper cracks in the center of
the strip; (c) edge cracks; and (d) alligatoring
55

56. 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
 The metal can forcing through a die in the same
direction or opposite direction.
hydraulic
piston
chamber
chamber
stock
die
extruded shape
hydraulic
piston
chamber
chamber
stock
die
extruded shape
hydraulic
piston
chamber
chamber
stock
die
extruded shape
56

57. TWO BASIC TYPES OF EXTRUSION:
 DİRECT EXTRUSİON: A metal billet is located into
a container, and a ram compresses the material, forcing
it to flow through one or more openings in a die at the
opposite end of the container.
 INDİRECT EXTRUSİON: The die is mounted to the
ram rather than at the opposite end of the container.
One advantage of the indirect extrusion process is that
there is no friction, during the process, between the
billet and the container liner.
57

58. DIRECT & INDIRECT EXTRUSION :
58

59. 59

60. HOT EXTRUSION:
 Keeping the processing temperature to above the re-
crystalline temperature.
 Reducing the ram force, increasing the ram speed, and
reduction of grain flow characteristics.
 Controlling the cooling is a problem. Glass may be used
as a lubricant.
COLD EXTRUSION:
 Keeping the processing temperature to below the re-
crystalline temperature.
 Often used to produce discrete parts. Increase strength
due to strain hardening, close tolerances, improved
surface finish, absence of oxide layer and high
production rates.
60

61. IMPACT EXTRUSION:
 Impact extrusion is performed at higher speeds and
shorter strokes than conventional extrusion. It is for
making discrete parts. For making thin wall-thickness
items by permitting large deformation at high speed.
61

62. ADVANTAGES OF EXTRUSION:
 Many shapes can be produced that are not possible with
rolling
 No draft is required
 Amount of reduction in a single step is only limited by
the equipment, not the material or the design
 Dies are relatively inexpensive
 Small quantities of a desired shape can be produced
economically
 High rate of production & Improved physical properties
 Economical and Design flexibility
DEFECTS OF EXTRUSION:
 Piping and Shape Error
 Internal Cracking
62

63. 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
63

64.  Large quantities of wires, rods, tubes and other sections
are produced by drawing process, which is basically a
cold working process.
 In this process the material is pulled through a die in
order to reduce it to the desired shape and size.
 In a typical wire drawing operation, once end of the wire
is reduced and passed through the opening of the die,
gripped and pulled to reduce its diameter.
64

65. DRAWING PRODUCTS:
 Electrical wire
 Cable
 Springs
 Welding Electrodes
 Metal bars
 Paper Clips
 Rods for shafts
ADVANTAGES:
- Close dimensional control
- Good surface finish
- Improved strength and hardness
- Adaptability to mass production
65

66. WIRE DRAWING:
 By successive drawing operation through dies of
reducing diameter the wire can be reduced to a very small
diameter.
 Tungsten Carbide dies are used to for drawing hard
wires, and diamond dies is the choice for fine wires.
66

67. DEEP DRAWING:
 This operation is extensively used to for making
cylindrical shaped parts such as cups, shells, etc from
sheet metal.
 As the blank is drawn into the die cavity compressive
stress is setup around the flange and it tends to wrinkle
or buckle (Fold) the flange.
67

68. STAGES OF DEEP DRAWING:
68

69. 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.
69

70. TUBE DRAWING:
70

71. ROD OR 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
71

72. ROD OR BAR DRAWING:
 The principles involved in the drawing of bar rod and
wire are the same, though the equipments used are
different for different sized products.
 Rods and tubes cannot be produced on draw benches.
 A long draw bench is used for drawing rods in straight
lengths. It consists of a die, a gripper and a lever for
pulling the rod and a chain used to transmit the power to
drive the cold drawing trolley.
72

73. DRAWING DEFECTS:
(a)Wrinkling in the flange or (b) in the wall
(c) Tearing, (d) Earing, (e) Surface scratches
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77. THANK YOU
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