me2030_20160329- metal forming- extrusion
TRANSCRIPT
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S. Suryakumar, ME, IITH ME2230: Manufacturing Processes – 1 1
ME2030: Manufacturing Processes – 1
Metal Forming: Extrusion & Drawing
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S. Suryakumar, ME, IITH ME2230: Manufacturing Processes – 1 2
Extrusion
Rolling Forging
Extrusion Stamping
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S. Suryakumar, ME, IITH ME2230: Manufacturing Processes – 1 3
Extrusion – It is a process where a billet is forced
through a die.
• Parts have constant cross-section
• Typical Products of Extrusion – Sliding Doors, tubing
having various cross-sections, structural andarchitectural shapes and door and window frames.
Drawing – It is a process where a cross-section of solid
rod, wire, or tubing is reduced or changed in shape
by pulling it through a die.
Extrusion & Drawing
Video
http://c/Users/Surya/Desktop/Vids/12a.%20Extrusion%20Processes.mp4http://c/Users/Surya/Desktop/Vids/12a.%20Extrusion%20Processes.mp4
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S. Suryakumar, ME, IITH ME2230: Manufacturing Processes – 1 4
Some Extruded Parts
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S. Suryakumar, ME, IITH ME2230: Manufacturing Processes – 1 5
Some Extruded Parts
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S. Suryakumar, ME, IITH ME2230: Manufacturing Processes – 1 6
Direct Extrusion
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Extrusion Analysis
Extrusion ratio, f
o x
A
Ar
Assuming all sections
are circular, ideal
deformation, no friction,
no redundant work: xr ln
Ram pressure
x f r Y p ln
Taking into account friction,where a =0.8 and b =1.2 to 1.5.
)ln( x f r baY p
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Extrusion Analysis
For direct extrusion, additional pressure, p f , required by the
extruder to overcome the wall friction is related as follows:
(1) [equilibrium equation]
For the worst case that the friction shear stress at the wall
equals to the shear yield strength of the work metal:
(2)
Subs. (2) into (1), the additional pressure:
The total ram pressure:
The power required:
L D p D p
oc
o f
4
2
/c s f p Y Y
o
f f D
LY p 2
o
x f D
LY p
2
Fv P
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• A billet 75mm long and 25mm in diameter is to be extruded in
a direct extrusion operation with extrusion ratio rx = 4.0. The
extrudate has a round cross section. The die angle (half angle)
= 900. The work metal has a strength coefficient = 415 MPa,
and strain-hardening exponent = 0.18. Use the Johnsonformula with a = 0.8 and b = 1.5 to estimate extrusion strain.
Determine the pressure applied to the end of the billet as the
ram moves forward.
Example
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Example
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Extrusion Dies
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Extrusion Dies
For the case of non-circular extruded section, a shape factor
has to be introduced:
where K x = shape factor C x = perimeter of the non-circular extruded section
C o = perimeter of a circle that has the same cross-
sectional area as the extruded section.
For direct extrusion, the extrusion force
25.2
02.098.0
c
x
x
C
C K
o
x f x D
LY K p 2
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• 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.
Impact Extrusion
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• The pressure required for extrusion is supplied through and incompressible
fluid medium surrounding the billet
• Brittle materials are extruded generally by this method
• Sealing is the major problem.
Hydrostatic extrusion
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a) Centre-burst: internal crack due to excessive tensile stress at the centre
possibly because of high die angle, low extrusion ratio.
b) Piping: sink hole at the end of billet under direct extrusion.
c) Surface cracking: High part temperature due to low extrusion speed and high
strain rates.
Extrusion Defects
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Wire and Bar Drawing
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