Bulk Drawing: Engineering Analysis

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Bulk Drawing Engineering Analysis
1. Introduction
In the bulk deformation processes, drawing is an
operation in which the cross section of a bar,
rod, or wire is reduced by pulling it through a
die opening, as shown in Figure 1.
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Figure 1 here
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Bulk Drawing Engineering Analysis
2. Objectives of the Analysis
Rolling process
Drawing process
Torque (force) Power Velocity (productivity) Max
draft
Pulling force
Power
Pulling velocity
Max draft
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3. Mechanics Phenomenon There is a tensile stress
due to pulling force, but compression still
plays a significant role since the metal is
squeezed down as it passes through the die
opening.
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4. Parameters
r area reduction A0 initial area of work Af
final area dD0-Df, draft Drawing stress
Contact length Die angle Friction between work
and die Force
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5. Drawing stress, drawing force, power
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5. Drawing stress, drawing force, power
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Allowable power Yield stress
6. Limit of Drawing
Maximum power lt Allowable power of a drive system
If not, material goes into plastic region no
drawing occurs, just elongation
Maximum stress lt Yield stress
Entire reduction not done in a single pass (done
in steps)
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6. Finding Max draw stress Max reduction (1
pass)
Assumption no friction, no strain hardening
(n0), no redundant work (perfectly plastic)
Max. draw stress Yield Strength
Also,
because (n0)
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Example
Wire stock of initial diameter 0.125 in. is
drawn through two dies each providing a 0.20 area
reduction. The staring metal has a strength
coefficient 40,000 lb/in.2 and a strain
hardening exponent 0.15. Each die has an
entrance angle of 12o, and the coefficient of
friction at the work-die interface is estimated
to be 0.10. The motors driving the capstans at
the die exists can each deliver 1.50 hp at 90
efficiency. Determine the maximum possible speed
of the wire as it exits the second die.
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