Metal forming

1. Unit I
Metal Forming
Prof. Karthik Silaipillayarputhur
School of Mechanical Engineering
SASTRA Deemed to be University
Thanjavur, TN
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2. Forging
 It is the forming of metal into the required shape
 It can be accomplished by hammering or pressing
 It is the oldest metal working art
 It can also be seen as a process where the desired shape is obtained through
plastic deformation of material. Plastic deformation is defined as a process in
which the object due to applied force changes its size or shape in a way that is
not reversible.
 Jobs produced by forging – clamps, bolts, nuts, rivets, automotive parts
 Wrought iron, mild steel, carbon steel, and alloy steel are used as raw materials
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3. Forging Classification
 Hot working
The mechanical working of metals above re-crystallization temperature is called
hot working
 Cold working
The mechanical working of metals below re-crystallization temperature is called
cold working
 Re-crystallization temperature is typically 0.3–0.4 times the melting point for
pure metals and 0.5 times for alloys
 The re-crystallization temperature is that temperature at which the crystal lattice
structure of the metal becomes reoriented. Consequently, the metal becomes
more workable and ductile.
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4. Forging – Hot working
 Hot working process may be generally classified as
Hand forging
Power forging
 Hand forging
These are mainly carried out in smithy shop
In smithy, small parts are first heated in in a furnace
Thereafter, the parts are shaped using forging tools under hand control
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5. Forging – Hot working
 Hand forging operations
Bending – it is an operation where a rod or pipe may bent.
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6. Forging – Hot working
 Hand forging operations
Drawing down - it is an operation of increasing the length of the bar and
reducing its thickness or width
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7. Forging – Hot working
 Hand forging operations
Swaging – it is a process that's used in the manufacturing industry to change the
size and shape of a work piece by exposing it to compressive forces
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8. Forging – Hot working
 Hand forging operations
Upsetting – it is a process of increasing the cross-section of a metal piece by
reducing its length
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9. Forging – Hot working
 Hand forging operations
Punching – it is a process of making holes by using a hot punch
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10. Forging – Hot working
 Hand forging operations
Fullering – process of reducing the diameter of work piece. Bottom fuller is held in
the hard die hole of the anvil and heated work piece is placed over it. Then top fuller
is placed over it and hammering operation is carried out till the work piece gets its
required thickness.
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11. Forging – Hot working
 Hand forging operations
Flattening – process of removing hammer and corrugation marks. This is done for
obtaining a smooth surface on the job. A flatter is used. This process is known as
flatting or setting down.
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12. Forging – Hot working
 Hand forging disadvantages
Not suitable for mass production
Components produced may not be uniform in dimensions
These defects are overcome by using machine forging
 Power forging
Forging machines are used to deform metallic work piece under the
action of repeated blows (hot working) or gradually increasing
pressure (cold working)
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13. Forging – Hot working
 Power Forging - Hammers in hot working
operations
 Drop hammer
In drop hammer, a piece of hot metal is
placed between specifically shaped dies.
A hammer is allowed to freely fall or drop
freely (when rollers are released) delivering a
blow which shapes the metal to the desired
form in one direction.
The hammer is termed as drop hammer
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14. Forging – Hot working
 Power Forging - Hammers in hot working operations
 Drop hammer
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15. Forging – Hot working
 Power Forging - Hammers in hot working operations
 Pneumatic hammer
Pneumatic hammer uses high pressure air developed by a compressor
The compressed air is delivered to the ram cylinder through the control
mechanism
The pressure air moves the ram downwards causing the top die to strike the
work piece placed between the top and bottom dies.
When the compressed air is delivered at the bottom of the ram cylinder, the
ram is lifted up
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16. Forging – Hot working
 Power Forging - Hammers in hot working operations
 Pneumatic hammer
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17. Forging Videos
https://www.youtube.com/watch?v=zskg3xKAR0Q
https://www.youtube.com/watch?v=aEatTMQsGtg
Drop hammer
https://www.youtube.com/watch?v=AdypXNcBaqU
Pneumatic hammer
https://www.youtube.com/watch?v=JNcf0Hej2Qk
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18. Rolling
 Rolling is a manufacturing process in which metal is passed through rollers to create
sheets or bars
 The rollers are power driven and the metal is regulated through an opening between the
rollers
 During rolling plastic deformation of the metal takes place
 The crystals of the metal are elongated in the direction of rolling
 The cross section of the work piece is reduced
 When the metal is heated and then rolled it is called hot rolling. When the metal is rolled
in cold condition it is called cold rolling. For hot rolling, steels are subjected to a
temperature of ~1000°C (above re-crystallization temperature). For cold rolling, metals
are below re-crystallization temperature 18

19. Rolling – Two high rolling mill
 It consists of two rolls in a housing. The upper roll is driven.
Two high rolling mill – non-reversing type
The two rolls revolve continuously in same direction therefore every time material is to
be carried back over the top of the mill for again passing in through the rolls. Such an
arrangement is used in mills through which the bar passes only once
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20. Rolling – Two high rolling mill
 It consists of two rolls in a housing. The upper roll is driven.
Two high rolling mill – reversing type
In two high reversing rolling mills the rolls rotate first in one direction and then in the
other, so that rolled metal may pass back and forth through the rolls several times.
These mills are also called multi pass rolling mills as rolling takes place in more than one
pass.
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21. Rolling – Three high rolling mill
 It consists of three rolls in a housing
 The rolls are of the same diameter arranged one over the other
 Gap between the middle roll and upper roll is less than the gap between middle and
lower roll
 The work piece is first passed through lower and middle rolls. Then, it is passed through
middle and upper rolls in the opposite direction
https://www.youtube.com/watch?v=KRn73gKQ2YU
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22. Extrusion - Direct
 Extrusion is a technique where a block of very hot metal is forced through a die to
produce components of a fixed cross-sectional area such as tubes and rods
 The extrusion ratio is defined as the starting cross-sectional area divided by the cross-
sectional area of the final extrusion
 The principle of extrusion is similar to the act of squirting tooth paste from a tube
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23. Extrusion - Direct
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24. Extrusion - Direct
 Extrusion is a process where a material undergoes plastic deformation by the application
of a force causing that material to flow through an orifice or die
 The material adopts the cross-sectional profile of the die
 The extruded part will be a solid piece.
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Extruded part
will be a solid
piece

25. Extrusion - Direct
 The extruded part can be a hollow piece depending upon the presence or absence of a
mandrel in the ram.
 All these are known as direct extrusion. In the direct process, the heated metal (billet) is
pushed by the ram through a stationary die to create the specified shape
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Extruded part
will be a hollow
piece

26. Extrusion - Indirect
 In the indirect method, the ram carries the die and applies pressure on to the stationary
billet, in the opposite direction of extrusion
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27. Wire Drawing
 It is a process of stretching a rolled rod through a die hole into small diameter wires
 The raw material is in the form of coiled rods
 The raw material is placed in hot dilute sulphuric acid to remove rust and scales
 Thereafter, they are washed with water
 After that, the coils may be dipped in lime
 The lime helps in keeping the lubricant thick and viscous
 The coils may be kept in baking ovens so that lime coating may harden and later act as a
lubricant during drawing
 The treated coil is passed through the die hole and drawn into fine wires 27

28. Wire Drawing
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29. Sheet Metal Forming
 In sheet metal work galvanized iron, aluminum, stainless steel, copper and tin plates or
sheets are used
 The sheets are specified in thickness by standard gauge numbers. Higher the gauge
number, smaller is the thickness
 Shearing is the operation of cutting off a sheet metal between a punch and a die
 Some shearing operations are
Blanking
Punching
Bending
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30. Shearing
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31. Sheet Metal Forming - blanking
 Blanking is the operation of cutting off a flat sheet of desired shape
 As punch descends upon the plate, high pressure is exerted by the punch
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32. Sheet Metal Forming - punching
 Punching is a type of sheet metal cutting process where scrap metal is removed from
larger pieces of sheet metal stock
 Shearing force is applied
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33. Sheet Metal Forming - bending
 Bending is the operation of straining a metal without change in thickness
 Angle bending - bending a sheet metal to a sharp acute angle
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34. Sheet Metal Forming - bending
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35. Introduction to CNC machining
 Computer Numerical Control (CNC) machining is a manufacturing process in which pre-
programmed computer software dictates the movement of factory tools and machinery
 Numerical control means a set of instructions (program) in the form of numbers, letters
and symbols. Program is directly fed into a computer by means of a keyboard
 The process can be used to control a range of complex machinery, from grinders and
lathes to mills
 CNC (Computer Numerical Control) machining is a subtractive manufacturing process
that uses computerized machine tools to make a custom-designed part
 A computer uses programming codes to direct machine tools to chip at (subtract) a
material. This is until the material forms the input designed part
 Very tight tolerances can be obtained 35

36. Introduction to CNC machining
 CNC machining’s mechanism can be divided into four different stages
 Create CAD design
 Convert CAD design to a CNC program
 Set up CNC machine
 Execute operation
https://www.youtube.com/watch?v=lEyNWtM6MW4
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38. Introduction to CNC machining
 CAD drawing is first created and checked for errors
 Based on the CAD drawing, CNC program (code) for the machining operation is done.
The code serves as an input
 The input is fed to the machine control unit (MCU)
 MCU controls the machine operation. Driving system provides precise motion control
for the tool and work piece
 Feedback helps the machine correct its speed or machining operation so that the desired
machining is precisely executed
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