ME2030_20160329- Metal Forming- Extrusion

8/18/2019 ME2030_20160329- Metal Forming- Extrusion

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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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Extrusion

Rolling Forging

Extrusion Stamping


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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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Some Extruded Parts


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Some Extruded Parts


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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



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



• 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



Example



Extrusion Dies



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



• 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



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



Wire and Bar Drawing


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Documents

ME2030_20160329- Metal Forming- Extrusion