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MANUFACTURING PROCESS-I
1. METAL FORMING PROCESSES
Hot working and cold working of metals – Forging processes – Open,
impression and closed die forging – Characteristics of the process – Types of
Forging Machines – Typical forging operations – Rolling of metals – Types
of Rolling mills - Flat strip rolling – Shape rolling operations – Defects in
rolled parts - Principle of rod and wire drawing -Tube drawing –– Principles
of Extrusion – Types of Extrusion – Hot and Cold extrusion – 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
Metal 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
Process:
A block is mounted in the drive section of lathe and
supported with tailstock. And the disk is attached with
head stock.
Spinning roller is attached with a T-rest lever bars.
It may suitable for both hot and cold working.
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9. Hot working- Advantages
Lower working force is enough to give shape.
Very dramatic shape change is possible.
Properties such as strength, ductility and toughness is
improved.
Density increases by removing voids.
Desired shape can be easily obtained under plastic
deformation.
Effect of impurities can be reduced.
Good grain structure.
Atoms in same direction leads to better strength.
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10. Hot working- disadvantages
Process 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.
Handling cost is high.
Automation is difficult one.
If the die or the tool wears the surface finish also
affects.
While 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 – “Minimum temperature at which the complete recrystallization of
a metal takes place with in a specified time”
TYPES OF COLD WORKING PROCESS
- Drawing
- Squeezing
- Bending
12. Cold working- Materials
Low and medium carbon steels
Low alloy steels
Copper 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
Widely applied as a forming process for steel.
Cold working is done at room temperature, so no
oxidation and scaling of work material occurs.
Excellent surface finish, which reduces the secondary
machining process.
High dimensional accuracy.
Highly suitable for mass production and automation,
because of low working temperature.
17. Cold working- Disadvantages
Strength of the metal is high, so large forces are needed
for deformation.
Complex shapes cannot be formed.
Tool must be specially designed, so high tool cost.
Stress formation in the metal during cold working is
higher. So this requires stress relieving.
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18. Cold working- limitations
It depends on the Chemical composition (percentage of
carbon or alloying) of the material.
The maximum limit is usually 0.45% of carbon for steels in
cold extrusion &1.6% for cold forging.
Larger 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 – Air pressure is used to lift the ram only.
- Double acting hammer – 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 – Air pressure is used for light work.
- Double acting hammer – 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
Upsetting:
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
Fullering:
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
Edging 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:
The 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
• TONGS :
Tongs are used mainly for
holding work of many
section.
• FLATTER :
Flatter is used to give
smoothness & accuracy to
articles which have already
been shaped by fullers and
swages.
• 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
• ANVIL :
Anvil is used for supporting hot job
while hammering is done for shaping
it into various shapes. It is made of
cast steel.
• SWAGE BLOCK :
It is used for holding hot bars during
bending, support for punching holes
in a job & various holes.
• FULLERS :
Fullers are used for necking down/to
form depressions.
48. YoucaN
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. 1.) Unfilled Section:
As 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.
This defect can be removed by proper die design, proper
availability of raw material and proper heating.
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50. 2.) Cold Shut:
Cold 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.
The fillet radius of the die should be increase to remove these
defects.
3.) Scale Pits:
Scale 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.
It can be removed by proper cleaning of forged surface.
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51. 4.) Die Shift:
Die 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.
This 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.
5.) Flakes:
These 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.
This defect can be removed by proper cooling.
6.) Improper Grain Growth:
This defect occurs due to improper flow of metal in casting which
changes predefine grain structure of product.
It can be removed by proper die design
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52. 7.) Incomplete Forging Penetration:
This defect arises due to incomplete forging. it is due to light or
rapid hammer blow.
This defect can be removed by proper control on forging press.
8.) Surface Cracking:
Surface cracking occurs due to exercise working on surfaces at low
temperature. In this defect, So many cracks arise on work piece.
This defect can be removed by proper control on working
temperature.
9.) Residual Stresses in Forging:
This defect occurs due to improper cooling of forged part. Too
much rapid cooling is main causes of this type of defects.
This can be removed by slow cooling of forged part.
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53. Rolling
Rolling is the process in which the metals and alloys
are plastically deformed into semi finished or
finished condition by passing between circular
cylinders.
Due to the frictional forces the metal is drawn into the
opening.
Metal Changes its shape due to high compressive
forces.
Both hot(for drastic shape changing) and cold
rolling(for finishing) process are there.
From 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
Two high rolling mills
Three high rolling mills
Four high rolling mills
Multi roll rolling mills
Universal rolling mills
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59. Two high rolling mills(single
direction)
Constant direction rolling
Upper rolls is moveable one to set the distance.
For single step reduction it is better one.
If successive reduction is need we have
to change the distance for each operations.
Least expensive
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60. Two high rolling mills(both
direction)
For successive reduction this is better than single
direction rolling.
We can set a different distance for each direction.
Two high reversing mills are often used for the first rolling
of an ingot into blooms and slabs.
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61. Three high rolling mills
Three rolls with constant direction
of rotation are arranged in a single vertical plane.
Lifting table used to rise or lower
the metal after each pass.
Both top and bottom rolls are driver rolls
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62. Four high rolling mills
The 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.
To 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. Multiple roll mills
By reducing the work roll diameter will produce
bending effect on the back up rolls.
So 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. Universal rolling mill
Metal reduction occurs in both
horizontal and vertical rolls.
Vertical rolls are mounted either one side
or both sides
Horizontal rolls may be either two, three
or four high arrangement.
Used 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
It is a cold working process in which the workpiece is
pulled through a tapered hole in a die so, the
diameter is reduced.
Wire can not be hot rolled economically smaller
than 5mm dia. So cold working is mainly used in wire
production
The starting material input for drawing is from the
extruded or rolled rods of 5 to 9mm.
Preparation of wire is important.(surface cleaning)
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82. Wire drawing
The die geometry is typically a bell shaped one.
The land serves to guide the wire or rod as it comes out
of the working zone of the die.
Material below 16mm diameter are handled in coil
form.
The 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.
Then the power reel rotates at a proper speed and pulls
the wire.
Coil speed is 25m/s.
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85. Rod drawing
Same as wire drawing process, here the product
must remain straight
The maximum length depends upon the carriage
movement distance
Here a moving chain arrangement is used to pull
the rod with a help of hook.
The pull capacity is 10kN to 1500kN.
Drawing 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 – 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
STEP 1: the billet piercing
STEP 2: the shell elongation
STEP 3: the tube sizing
STEP 4: the tube finishing
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99. Seamless tube manufacturing
When a round bar is subjected to radial compressive forces,
stresses develop at the center of the bar.
When 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.
The axes of the rolls are skewed in order to pull the round bar
through the rolls by the axial component of the rotary motion.
An internal mandrel assists the operation by expanding the
hole and sizing the inside diameter of the tube.
The mandrel may be held in place by a long rod, or it may be a
floating mandrel without a support.
Because 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
failure of the part during forming).
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