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F O R G I N G & E X T R U S I O N
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Transcript of F O R G I N G & E X T R U S I O N
- 1.FORGING & EXTRUSION
BULK DEFORMATION PROCESSES
2. FORGING
Simple forgings can be made with a heavy hammer & an anvil by
blacksmiths for centuries.
Nowadays a set of dies & a press are used.
We have open-die forging & closed-die forging.
Drawing out or reducing the cross-section of an ingot or billet to
lengthen it.
Upsetting or reducing the length of an ingot or billet to a larger
diameter.
Upsetting, drawing out, and piercing--processes sometimes combined
with forging over a mandrel for forging rough-contoured
rings.
3. OPEN-DIE FORGING
This form of forging generally involves placing a solid cylindrical
work piece between two flat dies (platens) and reducing its height
by compressing it. This is known as upsetting.
The specimen will develop a barrel shape. Barreling is caused by
frictional forces at die-workpiece interfaces that oppose the
outward flow of material at these interfaces. Barreling also occurs
in upsetting hot work pieces between cold dies.
4. UPSETTING A RECTANGULAR WORK-PIECE
The increase in thelength of the specimen is 40% the increase in
the width is 230%.
The reason for this is that the material flows in the direction of
least resistance.
a/h ratio is important & effects value of friction.
5. IMPRESSION-DIE FORGING
The sample adopts the shape of the die cavities (impressions) while
it is being upset between the closed dies.
Some of thematerial flows out radially & forms a flash.
The flash has a high (length/thickness ratio) a/h ratio, because of
which it is subjected to high pressure.
This means there is high frictional resistance tomaterial flow in
the radial direction in the flash gap. The high friction plays an
important role in the filling of the die cavities. Hence flash is
an important thing.
The flash also cools down more quickly. Hence it resists
deformation & encourages to fill cavity.
6. IMPRESSION-DIE FORGING
Complex shapes can be made.
The forging force increases gradually until flash starts to
form.
Then the forging load increases rapidly as the dies close
gradually.
The flash has a finite contact length with the die called land. The
land ensures that the flash generates enough resistance to the
outward flow of material which aids in die filling.
7. CLOSED-DIE FORGING
Similar to impression die but no flash forms. Work piece is
completely surrounded by dies & no excess metal is present for
flash.
Since no flash can form, proper control of material volume is
essential.
Under-sized blanks prevent complete filling of die. Over-sized
blanks may cause premature die failure or jamming.
Precision/flashless forging=near-net-shape production
Aluminum & Magnesium alloys are particularly useful for
precision forging because of the low forging loads, &
temperatures used.
8. OPEN-DIE FORGING
IMPRESSION-DIE FORGING
9. CLOSED-DIE FORGING
Steels & other alloys are more difficult to precision forge.
The choice between conventional & precision forging requires an
economical analysis.
Precision forging requires special dies.
Conventional forging requires machining steps to get final product
of desired shape.
10. MISCELLANEOUS FORGING
COINING: Minting of coins. High pressures of up to 5-6x material
yield point. Produces fine detail & surface finish.
HEADING: forming the heads of bolts, screws & nails. Buckling
may occur if the l:thick ratio is too high.
COGGING: Drawing out. Thethickness of the bar is reduced in
successive steps, without using large forces.
ROLL FORGING: cross-sectional area of bar is reduced & altered
in shape by passing it through rolls with grooves of various
shapes. Final products like tapered shafts, table knives produced.
Also used as a preliminary process followed by other forging
processes.
11. MISCELLANEOUS FORGING
SKEW ROLLING: similar to roll forging. Used for making ball
bearings. Round wire or rod is used. You can also upset a
cylindrical piece cut form a round bar.
FULLERING & EDGING:
12. ROLL FORGING
FORGING AN INGOT
COINING
13. DEFECTS
Surface cracking
Excessive material in the web can buckle during forging & form
a lap.
If the web is thick, the excess material can flow past the forged
parts & form internal cracks.
Small fillets & large filets. The material can fill large
radius better.
With small radii, the material folds over itself & produces a
lap called cold shut which can later on lead to failure of
part.
14. A FORGING DIE.
RIB, WEB, LAND, FILLET, FLASH, GUTTER, PARTING LINE, EXTERNAL (30
-50) & INTERNAL DRAFT ANGLES (70 - 100)
Common parts made by forging: crankshafts, connecting rods for
engines, turbine disks, gears, bolt heads, hand tools etc.
15. CRANKSHAFT
CONNECTING ROD
16. EXTRUSION
The basic extrusion process, a round billet is placed in a chamber
& forced through a die opening by a ram. The die may be of
various shapes.
Four basic types of extrusion:
Direct
Indirect
Hydrostatic
Impact
17. Hydrostatic Extrusion
Indirect Extrusion
Direct Extrusion
18. 19. IMPORTANT FACTORS
The extrusion ratio: R = AO /Af
AO =billet cross-sectional area
Af =area of extruded product
The pressure/force acting on material is dependent on R &
material yield point.
Any friction present will increase the amount of extrusion force.
Friction increases if die angle increases. At a certain angle,
friction is minimum.
20. IMPORTANT FACTORS
As extrusion speed & temperature increase, pressure increases.
Rate of work done. Sample gets heated up very quickly.
Incipient melting causes defects. Circumferential cracks due to hot
shortness may also develop.
The value of R can range from 10 to 100.
Ram speeds can go up to 100ft/min (0.5m/s)
Lower speeds are maintained for Al, Mg & Cu alloys. Steels, Ti
& other refractory metals can use higher speeds.
21. HOT EXTRUSION
Cooling of billet from high temperature needs to be uniform to
avoid inhomogeneous deformation.
Oxide layers very easily form which will affect the friction
coefficient between metal & container. Also, final product may
have oxide layer on it. Hence dummy block is made small.
22. SEAMLESS TUBES
23. SUMMARY