Mechanical Working of Metals (Extrusion and Drawing)

7/29/2019 Mechanical Working of Metals (Extrusion and Drawing)

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Extrusion and Drawing

Mechanical Working of Metals


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Definition of Extrusion

The basic

process of

forcing a metal

billet through ashaped die

Mainly used forSoft Metals such

as Aluminum or

Copper and

done hot


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EXTRUSION


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Tools in Extrusion

RAM DIE
http://www.precision-terrafirma.com/images/extrusiondies/ExtrusionDies2.jpghttp://www.kamkiu.com/My%20Webs/kk-English/extrusion_ram.jpg


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Extrusion Products


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SOLID

Cross Sections

HOLLOW

Cross Sections

PRODUCTS OF

EXTRUSION


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Types of Extrusion

Direct Extrusion

ram is separate

from the die

IndirectExtrusion

ram is with die


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Direct and Indirect Extrusion


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Difference between Direct and

Indirect Extrusion

Indirect Extrusion

requires lower

extrusion loads

since less frictionis encountered!

Disadvantage in Indirect

Extrusion:

a) Difficulty in supporting

extruded products

b) Lower rigidity of die


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Extrusion Load Profile

Increases initially

as metal is being

upset into die

Increases

after 85% of

the metal hasbeen

extruded

Load

Decreases

during

extrusion

proper


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Extrusion Ratio

rx= extrusion ratioAo = area initial

Af = area final

Extrusion ratio of 35:1

to 100:1 is done in the

industry!


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Extrusion Work

Work = Force x Distance

Wx = xV lnr

Extrusion ratio affects the

amount of work required to

do extrusion!


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Effect of Die Angle on

Extrusion Load


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Effect of Die Angle

Low die angle

surface area is large, leading to:

increased friction at die-billet interface & higher

friction results in larger ram force

Large die angle

more turbulence in metal flow during reduction:

Turbulence increases ram force required


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Optimum Die Angle

Optimum angle depends on work material, billet

temperature, and lubrication!


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Redundant Work

Refers to work required to bend the metal one way

and then bend it back to its original direction!


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Effect of Die Shape on

Extrusion Load

VS

As the die orifice shape becomes more

complex, higher loads are required!


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Extrusion Load Analysis

USE SLAB METHOD TO DETERMINE

EXTRUSION LOAD


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Actual Extrusion Pressure

044

2

0

2

0 d

ddPd

d xxoxx

o

oxd

x

4exp

Summation of Forces along the horizontal:

x = extrusion pressure profile

when length x is inside the

container

o = yield stress

= coefficient of friction

do = initial diameter

x = length of billet inside thecontainer

o

oxd

x

41


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Sample Problem

A 4 long billet with diameter = 1.25 is direct

extruded to a diameter of 0.50. For the work

metal, y = 45,000 lb/in2 and coefficient of

friction is 0.30.

Determine:

(a) extrusion ratio

(b) extrusion strain

(c) ram pressure at L = 4.0, 2.5, 1.0 and 0.


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Mean Extrusion Pressure

o

oxd

x

41

o

oo

dL 41max o min

o

omeand

L

21

2

minmax

When L = Lo When L =0


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Extrusion Load

o

o

oox A

d

LF

21

Extrusion Force = Mean Pressure x Area of Contact


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Extrusion Work

rVd

LWo

oextrusion ln21

This work equation may also betransformed to calculate for the

power required to extrude a metal!

Wx = xV lnrRECALL:


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Sample Problem

For the given extrusion problem, if the ram was

moved at a rate of 1.0 per 150 seconds,

determine:

(a) mean extrusion load

(b) extrusion work

(c) power required for this operation(1 HP = 33,000 ft-lb/min)


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Sample Problem

During the extrusion of a steel billet 1.5 m

long, 640 mm diameter it was noted that

the extrusion load was 128 MN when the

ram was 1/3 of the way through the cycleand 111.6 MN when through. Calculate

the coefficient of friction in the chamber.


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Wire Drawing


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Definition of Wire Drawing

Wire drawing is a metal-reducing process

in which a wire rod is pulled through a

single die or a series of continuous dies,

thereby reducing its diameter.

Various wire temperscan be produced by

a series of drawing and annealing

operations. (Temperrefers to toughness.)


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Wire Drawing


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Deep Drawing


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Products of Deep Drawing
http://images.google.com.ph/imgres?imgurl=http://www.alfed.net/images/Pots.jpg&imgrefurl=http://www.alfed.net/health.htm&h=337&w=484&sz=28&tbnid=Pq16L_ePl0sJ:&tbnh=87&tbnw=125&start=6&prev=/images%3Fq%3Dmetal%2Bcooking%2Bpots%26hl%3Dtl%26lr%3Dhttp://images.google.com.ph/imgres?imgurl=http://www.txantiquemall.com/2step/c2_bullets.gif&imgrefurl=http://www.txantiquemall.com/2step/2step_c.htm&h=142&w=150&sz=17&tbnid=Dehvz-Ifs2EJ:&tbnh=85&tbnw=90&start=2&prev=/images%3Fq%3Dbullet%2Bcasings%26hl%3Dtl%26lr%3D%26sa%3DNhttp://www.pmfind.com/images4/preform1.jpg


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Wire Drawing Products

WIRES

ROD STOCKS


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Die Tandem


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Drawing Series

Since wire drawing is normally done cold,annealing is sometimes necessary

between dies


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Drawing Die

The longer the bearing, the

longer the life of the die!


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Features of a Draw Die

a) Entryregion - funnels lubricant into the die to

prevent scoring of work and die

b) Approach- cone-shaped region where drawingoccurs

c) Bearing su rface- determines final stock size

d) Back rel ief- exit zone - provided with a backrelief angle(half-angle) of about 30

Die materials: tool steels or cemented carbides


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Extrusion vs Drawing


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Drawing Load


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Drawing Load Analysis


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Drawing Stress

Slab analysis will yield the equation for the

drawing stress as follows:

B

o

f

odd

d

B

B2

11

B= cot


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Drawing Load

4

11

22

f

B

o

f

od

d

d

d

B

BF

Drawing Load = Drawing Stress x Final Area


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Drawing Strain

Drawing Strain is expressed in terms ofreduction in area, R

o

fo

AAAR

Ao = area initial

Af= area final

In Drawing, maximum possible drawing strain is achieved

when:

drawing stress = flow stress of metal


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Sample Problem

Determine the maximum possible drawing

strain if steel wire (YS=140 MPa) is drawn

with die angle 4o

and coefficient of frictionis 0.20.


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Sample Problem

Rod stock is drawn through a draw die with anentrance angle(2) of 12. Starting diameter =0.50 and final diameter = 0.35. Coefficient of

friction at the die-work interface = 0.10.Determine:

(a) area reduction

(b) drawing load for the operation(c) horsepower to perform the operation if theexit velocity of the stock = 2 ft/sec.


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Sample Problem

Calculate the drawing load required to

achieve 30% reduction in area on a 10-

mm diameter copper wire, given that the

yield stress of the metal is 235 MPa, dieangle is 8o and coefficient of friction is

0.08.


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Advantages of Hot Working

Decrease in energy required for

deformation

Increased ability of metal to flow without

cracking

Rapid diffusion decreases chemical

inhomogeneities

Elimination of blowholes and porosities

Refinement of coarse columnar grains to

fine equiaxed grains


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Disadvantages of Hot Working

Oxidation results to metal losses

Reactive metals require inert atmosphere

Decarburization of steels

Poor surface finish

Greater dimensional tolerance required

Less uniform structure and properties


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Ideal Extrusion Load

Work = Force x Distance

Wx = yV lnr

Px = y

lnr

Fx = ylnrAo

Mechanical Working of Metals (Extrusion and Drawing)

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