drawing - iit bombayramesh/courses/me206/drawing.pdfcold drawing 5 a.durer -wire drawing mill (1489)...
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1
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
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