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Metal Forming Processes
1. METAL FORMING PROCESSES
Hot working and cold working of metals â Forging processes â Open,
impression and closed die forging â Characteristics of the process â Types
of Forging Machines â Typical forging operations â Rolling of metals â
Types of Rolling mills - Flat strip rolling â Shape rolling operations â
Defects in rolled parts - Principle of rod and wire drawing -Tube drawing ââ
Principles of Extrusion â Types of Extrusion â Hot and Cold extrusion â
Equipments used.
2. HOT WORKING OF METALS
Mechanical working of a metal above the recrystallization temperature
but below the melting point.
Plastic deformation of metals and alloys under the condition of
temperature and strain rate.
Recrystallization temperature is 30 to 40% of melting temperature.
In this process, Metal is heated above the RT with 0.7 to 0.9 times of
the melting temperature.
TYPES OF HOT WORKING PROCESS
-Hot forging
-Hot Rolling
-Hot Extrusions
-Drawing
-Swaging
-Hot Spinning
7. Hot spinning
īMetal spinning, also known as spin forming or
spinning or metal turning most commonly, is a
metalworking process by which a disc or tube of
metal is rotated at high speed and formed into an
axially symmetric part. Spinning can be performed by
hand or by a CNC lathe.
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8. Hot spinning
īProcess:
īA block is mounted in the drive section of lathe and
supported with tailstock. And the disk is attached with
head stock.
īSpinning roller is attached with a T-rest lever bars.
īIt may suitable for both hot and cold working.
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9. Hot working- Advantages
īLower working force is enough to give shape.
īVery dramatic shape change is possible.
īProperties such as strength, ductility and toughness is
improved.
īDensity increases by removing voids.
īDesired shape can be easily obtained under plastic
deformation.
īEffect of impurities can be reduced.
īGood grain structure.
īAtoms in same direction leads to better strength.
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10. Hot working- disadvantages
īProcess takes place at higher temperature that Is above
7300
C, So special protection of machines is necessary
other wise machine and tool life is minimum.
īHandling cost is high.
īAutomation is difficult one.
īIf the die or the tool wears the surface finish also
affects.
īWhile the objects cools form its recrystallisation
temperature, due to shrinkage of the parts dimension
may vary.
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11. COLD WORKING OF METALS
Plastic deformation of a metal to the required shape being performed
below the recrystallization temperature.
Process will work under room temperature.
RT â âMinimum temperature at which the complete recrystallization
of a metal takes place with in a specified timeâ
TYPES OF COLD WORKING PROCESS
- Drawing
- Squeezing
- Bending
12. Cold working- Materials
īLow and medium carbon steels
īLow alloy steels
īCopper and light alloy such as aluminium,
magnesium, titanium.
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13. 1.0 Drawing
- Blank Drawing
Cutting a flat shape from the metal.
-Tube Drawing
Tube piercing is called tube drawing
-Embossing
Process of making raised or projected design
on the surface of the metal.
-Wire Drawing
Diameter less than 16mm has drawn in the
form of wire coil.
-Metal Spinning
14. 2.0 Squeezing
- Coining
-Sizing
Size the metal to required shapes
-Swaging
It is used for producing rounded
components through radial impact forces
by reciprocating dies.
-Knurling
The rolls are pressed radially against the
rotating work piece, to make grip on the
handles.
15. 3.0 Bending
Bend into Desired shape like rods, wires, bars
- Plate Bending
Large Plates are bent to shapes
- Roll Forming
-It carries three rolls, Two are fixed and the third one is adjustable.
Diameter of all rolls are same.
- Angle Bending
Angles, Circles, Ovals
16. Cold working- Advantages
īWidely applied as a forming process for steel.
īCold working is done at room temperature, so no
oxidation and scaling of work material occurs.
īExcellent surface finish, which reduces the secondary
machining process.
īHigh dimensional accuracy.
īHighly suitable for mass production and automation,
because of low working temperature.
17. Cold working- Disadvantages
īStrength of the metal is high, so large forces are needed
for deformation.
īComplex shapes cannot be formed.
īTool must be specially designed, so high tool cost.
īStress formation in the metal during cold working is
higher. So this requires stress relieving.
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18. Cold working- limitations
īIt depends on the Chemical composition (percentage of
carbon or alloying) of the material.
īThe maximum limit is usually 0.45% of carbon for steels
in cold extrusion &1.6% for cold forging.
īLarger Grain size is easy for cold working.
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19. Hot working Cold working
Working above recrystallization
temperature
Working below recrystallization
temperature
New crystals are formed New crystals are not formed
It hardens the metal No hardening
Impurities are removed from the metal Impurities are not removed from the
metal
Elongation of metal takes place Elongation decreases
Large size metals also deformed Limited to size
Internal stress is not formed Internal stress is formed.
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20. FORGING PROCESSES
The desired shape is obtained by the application of a compressive force.
Types
1.0 Smith or Open die Forging
The forging is done in a heated work at the proper temperature by
placing on flat surface anvil through hammering the metal piece.
a) Hand Forging
b) Power Forging
24. TYPES OF FORGING MACHINES
1.0 Air and Steam Hammer
a) Air Hammer
It using air or steam.
- Single acting hammer â Air pressure is used to lift the ram only.
- Double acting hammer â Air pressure is used to lift the ram and
Impact the work piece.
25. 1.0 Air and Steam Hammer
b) Steam Hammer
It using air or steam.
- Single acting hammer â Air pressure is used for light work.
- Double acting hammer â Air pressure is used for heavy work.
26. 2.0 Mechanical Hammer
a) Helve Hammer
b) Trip Hammer
The reciprocating ram is the main part and it is toggle. The stroke length
various from 175 to 400blows/min.
27. 2.0 Mechanical Hammer
c) Level Spring Hammer
d) Pneumatic Hammer
An elastic rod is used to operate the ram. The stroke length various from 40
to 200blows/min.
28. TYPES OF FORGING OPERATIONS
1.0 Upsetting
The metal is heated at one end and the force is applied on the
other end by using hammer. The cross sectional area will increase and
length will decrease.
29. TYPES OF FORGING OPERATIONS
3.0 Punching
In this process, making of a hole in a
given job.
4.0 Bending
In this process, shapes like angles,
ovals and circle can be made.
2.0 Drawing Down
In this process, the cross
sectional area will decrease and length will
increase.
30. TYPES OF FORGING OPERATIONS
6.0 Forge Welding
Joining the work pieces by forging
operation.
7.0 Piercing
Making a blind or through holes with the help of a punch in the metal.
5.0 Cutting
Removal of excess metal from the work.
31. TYPES OF FORGING OPERATIONS
8.0 Swaging
Reducing or changing the cross sectional area of the metal.
9.0 Flattering
Used to flat the stock and that the stock is fitted properly in the closed die.
10.0 Fullering
Reducing the stock and increasing the length of the work piece by applying
pressure.
33. Forging operations
īUpsetting:
The length is shortened and either or both its thickness
and width increased, the piece(stock) is said to be
upset. This operation is upsetting. Increase the cross
sectional area. (bolt manufacturing)
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37. Forging operations
īFullering:
Reducing the cross section at the center plane and
increases its length.
This technique is commonly used to make the internal
combustion of engines.
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38. Forging operations
īEdging OR Rolling:
Distribute the metal longitudinally by moving metal
from the portion of higher cross section and
increases its length by compressive force.
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39. Forging operations
Punching and blanking:
īThe most common shearing operations are punching-
where the sheared slug is scrap or may be used for some
other purpose-and blanking-where the slug is the part
to be used and the rest is scrap.
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44. FORGING TOOLS
44
âĸ TONGS :
Tongs are used mainly for
holding work of many
section.
âĸ FLATTER :
Flatter is used to give
smoothness & accuracy to
articles which have already
been shaped by fullers and
swages.
âĸ SWAGE :
Swage is used to
reduce/finish to round,
square/hexagonal form. It
consists of two parts-The
top part having a handle.
The bottom part having a
square shank.
45. 45
45
âĸ ANVIL :
Anvil is used for supporting hot job
while hammering is done for shaping
it into various shapes. It is made of
cast steel.
âĸ SWAGE BLOCK :
It is used for holding hot bars during
bending, support for punching holes
in a job & various holes.
âĸ FULLERS :
Fullers are used for necking down/to
form depressions.
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Defects of metal forged product include exterior cracking, interior
cracking, laps, cold shuts, warping of the part, improperly formed
sections and dead zones. Cracking both interior and exterior is caused by
excessive stress, or improper stress distribution as the part is being
formed. Cracking of a forging can be the result of poorly designed
forging die or excess material in the work piece. Cracks can also be
caused by disproportionate temperature distributions during the
manufacturing operation. High thermal gradients can cause cracks in a
forged part.
49. ī1.) Unfilled Section:
īAs the name implies in this type of defect some of the
forging section remain unfilled. This is due to poor design
of die or poor forging technic. This is also due to less raw
material or poor heating.
īThis defect can be removed by proper die design, proper
availability of raw material and proper heating.
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50. ī2.) Cold Shut:
īCold shut includes small cracks at corners. These defects occur
due to improper design of forging die. It is also due to sharp
corner, and excessive chilling in forge product.
īThe fillet radius of the die should be increase to remove these
defects.
ī3.) Scale Pits:
īScale pits are due to improper cleaning of forged surface. This
defect generally associated with forging in open environment. It
is irregular deputations on the surface of forging.
īIt can be removed by proper cleaning of forged surface.
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51. ī4.) Die Shift:
īDie shift is caused by misalignment of upper die and lower die.
When both these dies are not properly aligned the forged
product does not get proper dimensions.
īThis defect can be removed by proper alignment. It can be done
by provide half notch on upper die and half on lower die so at the
time of alignment, both these notches will matched.
ī5.) Flakes:
īThese are internal cracks occur due to improper cooling of forge
product. When the forge product cooled quickly, these cracks
generally occur which can reduced the strength of forge product.
īThis defect can be removed by proper cooling.
ī6.) Improper Grain Growth:
īThis defect occurs due to improper flow of metal in casting which
changes predefine grain structure of product.
īIt can be removed by proper die design
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52. ī7.) Incomplete Forging Penetration:
īThis defect arises due to incomplete forging. it is due to light or
rapid hammer blow.
īThis defect can be removed by proper control on forging press.
ī8.) Surface Cracking:
īSurface cracking occurs due to exercise working on surfaces at
low temperature. In this defect, So many cracks arise on work
piece.
īThis defect can be removed by proper control on working
temperature.
ī9.) Residual Stresses in Forging:
īThis defect occurs due to improper cooling of forged part. Too
much rapid cooling is main causes of this type of defects.
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53. Rolling
īRolling is the process in which the metals and alloys
are plastically deformed into semi finished or
finished condition by passing between circular
cylinders.
īDue to the frictional forces the metal is drawn into
the opening.
īMetal Changes its shape due to high compressive
forces.
īBoth hot(for drastic shape changing) and cold
rolling(for finishing) process are there.
īFrom the start ingot- blooms- billet- slaps which are
further rolled into plat, sheet, rod, bar, pipe, rails.
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58. Rolling mills classifications
Classifications based on number of rolls
īTwo high rolling mills
īThree high rolling mills
īFour high rolling mills
īMulti roll rolling mills
īUniversal rolling mills
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59. īTwo high rolling mills(single
direction)
īConstant direction rolling
īUpper rolls is moveable one to set the distance.
īFor single step reduction it is better one.
īIf successive reduction is need we have
to change the distance for each operations.
īLeast expensive
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60. īTwo high rolling mills(both
direction)
īFor successive reduction this is better than single
direction rolling.
īWe can set a different distance for each direction.
īTwo high reversing mills are often used for the first
rolling of an ingot into blooms and slabs.
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61. īThree high rolling mills
īThree rolls with constant direction
of rotation are arranged in a single vertical plane.
īLifting table used to rise or lower
the metal after each pass.
īBoth top and bottom rolls are driver rolls
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62. īFour high rolling mills
īThe bending of the roller is less if the diameter of the
roller is high. At the same time the power consumption
and force P value also very high for big diameter rollers.
īTo over come this problem small Diameter rollers
with larger diameter back up rollers are used. This
can be used for both directions.
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63. īMultiple roll mills
īBy reducing the work roll diameter will produce
bending effect on the back up rolls.
īSo in multiple roll mills a cluster of 6, 12, 20 rolls are
used to manufacturing strips. Form 0.001mm thick and
2000 mm wide.
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In four high rolling the diameter of the back up rolls can
not be greater that 2 to 3 times that of the work rolls.
65. īUniversal rolling mill
īMetal reduction occurs in both
horizontal and vertical rolls.
īVertical rolls are mounted either one
side or both sides
īHorizontal rolls may be either two, three
or four high arrangement.
īUsed for roll wide strips, sheets, plates
and slabs that requires both rolling edges
and also for rolling of H sectioins.
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70. Roll force
F= contact Length* width of strip * average ture stress
=L * w * True stress average
Power per roll
P= 2*3.14*Force* Length * speed in rpm / 6000
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74. SHAPE ROLLING OPERATIONS
1.0 Ring rolling
A thick ring is expanded into a large diameter ring with a reduced cross
section. The ring is placed in between two rolls and one of the roll is driven , ring
thickness is reduced.
Advantages:
-Close tolerances
-Material Saving
- Short production times
75.
76. SHAPE ROLLING OPERATIONS
2.0 Thread rolling
Straight or tapered threads are formed. Threads are formed on the rod ,
with each stroke of a pair of flat reciprocating dies
Advantages:
-Surface finish
good
-Long life
- Thread strength
is good
77. DEFECTS IN ROLLED PARTS
1.0 Surface Defects
It includes scale, rust, cracks and pits due to impurities and inclusion
2.0 Internal Structural Defects
Strain on the material should adjust.
78.
79. DEFECTS IN ROLLED PARTS
3.0 Other Defects
a)Homogeneous deformation of element across the width
Due to decrease in thickness for the elements near the centre will be mainly converted
into increase in length and near the edge the decrease in thickness is converted into
lateral spread.
b) Homogeneous deformation in the thickness section
Due to reduction in height is converted into increase in length and the thickness of the
sheet does not undergo the same lateral deformation.
c) Folds
It is created during plate rolling if the reduction per pass is very small.
d) Lamination
Due to incomplete welding of pipe and blowholes during the rolling process the internal
defects such as fissures are created.
81. Drawing of wire, rod and tube
īIt is a cold working process in which the workpiece
is pulled through a tapered hole in a die so, the
diameter is reduced.
īWire can not be hot rolled economically smaller
than 5mm dia. So cold working is mainly used in wire
production
īThe starting material input for drawing is from the
extruded or rolled rods of 5 to 9mm.
īPreparation of wire is important.(surface cleaning)
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82. Wire drawing
īThe die geometry is typically a bell shaped one.
īThe land serves to guide the wire or rod as it comes
out of the working zone of the die.
īMaterial below 16mm diameter are handled in coil
form.
īThe one end of the wire is gripped with a plier or
carriage which pulls the rod through all zones of the
die hole where it under goes deformation or
elongation. Then it is rolled on a power reel.
īThen the power reel rotates at a proper speed and
pulls the wire.
īCoil speed is 25m/s.
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85. Rod drawing
īSame as wire drawing process, here the product
must remain straight
īThe maximum length depends upon the carriage
movement distance
īHere a moving chain arrangement is used to pull
the rod with a help of hook.
īThe pull capacity is 10kN to 1500kN.
īDrawing speed may be
For larger size rod 0.15m/s
For smaller size rod 1.5m/s
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91. EXTRUSION
Heated metal is compressed
and forced through a suitable
shaped die â Hot Extrusion.
Cold extrusion is non heated
metal but force is required
and used for commercial
metals.
95. Seamless tube manufacturing process
OR
Mannesmann cross roll piercing mill
OR
Rotary tube piercing
īSTEP 1: the billet piercing
īSTEP 2: the shell elongation
īSTEP 3: the tube sizing
īSTEP 4: the tube finishing
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99. Seamless tube manufacturing
īļWhen a round bar is subjected to radial compressive forces,
stresses develop at the center of the bar.
īļWhen it is subjected continuously to these cyclic compressive
stresses, the bar begins to develop a small cavity at its
center, which then begins to grow.
īļThe axes of the rolls are skewed in order to pull the round bar
through the rolls by the axial component of the rotary motion.
īļAn internal mandrel assists the operation by expanding the
hole and sizing the inside diameter of the tube.
īļThe mandrel may be held in place by a long rod, or it may be a
floating mandrel without a support.
īļBecause of the severe deformation that the bar undergoes, the
material must be high in quality and free from defects (since
internal defects may propagate rapidly and cause premature
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