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Drawing

ME 206: Manufacturing Processes IInstructor: Ramesh Singh; Notes by: Prof. S.N. Melkote / Dr. Colton

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Outline

• Rod/Wire Drawing Introduction• Rod/Wire Drawing Analysis• Rod/Wire Drawing Defects

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Equipment

4Cold Drawing

5 A. Durer - Wire Drawing Mill (1489)(copper wire)

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Rod/Wire Drawing Introduction• Basic Process: A metal rod is pulled through a die by

application of a tensile force at die exit

Wire Drawing Machine

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Process Variations• Tube drawing

Source: Todd, Allen, Alting, 1994

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Rod/Wire Drawing Introduction• Deformation mechanism: most of the plastic flow is caused by

compression force which arises from the reaction of the metal with the die

Bar, wire and tube drawing are usually carried out at room temperature. Temperature rise is considerable during the process because of large deformations

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Rod/Wire Drawing Introduction• Drawing Practice:

fine wires: 15-25% reductioncoarse wires: 20-50% reductiondrawing speeds: 30-300ft/min; up to 10,000ft/mindrawing loads: up to 300,000lb

• Dies: tool steels and carbide; coatings SCD/PCD

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Key Process Variables• Reduction:

• Die angle (usually 6°-15°)

• Interfacial friction

• Drawing speed, Vf

-= -1o f f

o o

A A AA A

Source: S. Kalpakjian & S. Schmidt, 4th ed. 2003

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Lubrication• Lubrication:

soft metal coatings for dry drawing

grease, powder, soap

entire die immersed in lubricating fluid for wet drawing

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Rod/Wire Drawing Analysis

• Objectives– Find the drawing stress, force and power

required under ideal deformation conditions

– Find drawing stress, force, power including effects of friction and redundant work of deformation

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Rod/Wire Drawing Analysis

• Ideal deformationExternal work = Work of ideal plastic deformation

for

( ) ( )

ttd

ffd

du

LAuLAt

ess

se

ò==

=

0ntt Kes =

÷÷ø

öççè

æ==

+=

fftft

nt

d AAYY

nK 0ln1

eees

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Rod/Wire Drawing Analysis

• Ideal deformationDrawing force, Fd = sdAf

Drawing power, Pd = Fd Vf

Source: S. Kalpakjian & S. Schmidt, 4th ed. 2003

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Rod/Wire Drawing Analysis

• Ideal deformation + frictionAssumptions of “slab” analysis applyUsing slab analysis we get

úú

û

ù

êê

ë

é

÷÷ø

öççè

æ-÷÷

ø

öççè

æ+=

aµ

µas

cotf

fd A

AtanY

011

Source: S. Kalpakjian & S. Schmidt, 4th ed. 2003

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Rod/Wire Drawing Analysis• Ideal deformation + friction + redundant deformation

• Die pressure, p = Yf - sd

24 11 13 3

cotf

do

Atan rY

A r

µ aas a

µ

ì üé ùæ öæ ö -ï ïæ öê ú= + - +í ýç ÷ç ÷ ç ÷è øê úè ø è øï ïë ûî þ

213

od

f

AY ln

Aµs aa

ì üæ öï ïæ ö= + +ç ÷í ýç ÷ ç ÷è øï ïè øî þfor small a

Source: S. Kalpakjian & S. Schmidt, 4th ed. 2003

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Rod/Wire Drawing Analysis

• Effect of die angle

Source: S. Kalpakjian & S. Schmidt, 4th ed. 2003

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Rod/Wire Drawing Analysis

• Main factor limiting maximum reduction per pass in drawing:

– Yield of material at die exit

– Drawing limit is reached when sd = Yf

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Drawing Limit

• Ideal deformation of a perfectly plastic material

1

11 0.63 63%

od

f

o od

f f

o f

o

AY ln

A

Y

A Aln e

A A

Maximum reduction per passA AA e

e

e

s

s

s s

æ ö= × ç ÷ç ÷

è ø=

æ ö= Þ = Þ =ç ÷ç ÷

è ø

-= = - = =

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Drawing Limit

• Ideal deformation of a strain hardening material

e

s

n+1

ideal+frictionideal

es

ds ds1

( 1)

1

1

1

no

df

n

d

o f n

o

A KY ln

A n

Kn

Maximum reduction per passA A

eA

e

e

es

s es s e

+

- +

æ ö= × =ç ÷ç ÷ +è ø== Þ = +

-= = -

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Example ProblemAssuming zero redundant work and frictional work to be 20% of the ideal work, derive an expression for the maximum reduction in area per pass for a wire drawing operation for a material with a true-stress strain curve of s=Ken

Total work = Ideal work + frictional work + redundant workTotal work = Ideal work + 0.2 x Ideal work = 1.2 x Ideal work

Or, Total work of deformation = 1.2 [u x volume] … (1)

In drawing, external work of deformation = sd x volume … (2)Equating (1) and (2), we get

sd = 1.2u or

0

12.12.12.1

11

00

11

+===

+

òò nKdKd

n

tntttd

eeeessee

12.1 es Yd = where … (3)÷÷ø

öççè

æ=

fAA0

1 lne

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Example ProblemMax reduction occurs when total drawing stress, sd = Flow stress of material at die exit, Y

÷øö

çèæ +-

+

+

-=-

=\

=Þ+

=Þ+

=

=+

=

=

2.11

0

0

2.11

001

1

11

11

1 passper reduction max

2.11

ln2.111

2.1

2.1

nf

n

ff

nn

nd

eAAA

eAAn

AAn

KnK

KYY

e

ee

ee

s

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Rod/Wire Drawing Defects• Centerline cracking

Center cracking in extruded barCenter cracking increases with:

• increasing die angle a

• decreasing reduction per pass

• friction

• presence of inclusions

Source: S. Kalpakjian & S. Schmidt, 4th ed. 2003

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Rod/Wire Drawing Defects

• Seams: longitudinal scratches or folds on surface of material

• Residual stresses– Common in cold drawn wire/tube– Stress pattern a function of amount of

reduction/pass– Increases with reduction per pass

Source: S. Kalpakjian & S. Schmidt, 4th ed. 2003

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Summary

• Rod/Wire drawing basics• Rod/wire drawing analysis

– Slab analysis• Rod/wire drawing defects