Introduction%20To

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Introduction To Manufacturing Systems by Ed Red
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• Fundamentals of Metal Forming
• Metal forming is plastic deformation of metals
  into desired shapes
• Deformation stresses may be tensile or
  compressive (usually compressive)
• Metals must exhibit certain properties to be
  formed efficiently
• Friction is an important factor in metal forming
• Strain rate and temperature are important
  factors in metal forming

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Material Behavior in Metal Forming Engineering
Stress and Strain (used by engineering
designers) Engineering stress se
F/Ao Engineering strain e (L -
Lo)/Lo Hooke's Law (elastic region) se E e
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Material Behavior in Metal Forming Stress -
strain diagrams (tensile and compression)
Ultimate strength
se
Yield strength
e
0.2 offset
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Material Behavior in Metal Forming Common
parameter values Al Steel E psi 10 x
106 30 x 106 MPa 70 x 103 210 x
103 Yield strength psi 4000 60,000 MPa
28 400 Ultimate strength psi 10,000
90,000 MPa 70 600
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e
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Material Behavior in Metal Forming
Why do engineering designers base their design on
engineering stress/strain, but manufacturing
engineers use true stress-strain?
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Material Behavior in Metal Forming
Strain hardening - Resistance to increasing
strain. Stress-strain can be related in the
plastic region by the form s K en where K
is the strength coefficient and n is the
hardening exponent. A log-log diagram will show
the linear behavior expected for a curve of this
form. Note The greater the n, the greater the
strain hardening effect. Necking for many ductile
materials begins approximately when the true
strain reaches a value equal to n.
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Material Behavior in Metal Forming
Material Strength coeff, K Strain
hardening exp, n psi MPa Aluminum 30,0
00 210 0.18 Steel 125,000
850 0.15
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Material Behavior Example
The following data are collected during a tensile
test in which the initial gage length is 5 in.
and the cross-sectional area is 0.1 in2 Load
(lb) 0 4000 5180 6200 6500 6200 4600 Length
(in) 5.000 5.009 5.25 5.60 5.88 6.12 6.40 Determi
ne the yield strength Y, modulus of elasticity
E, and tensile strength TS. Also determine the
strength coefficient K and the hardening exponent
n.
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Some relations you need to know
s se (1 e) e ln (1 e) Also note that it
is often necessary to use a constant volume
relationship for modeling process phenomena. In
the case of a tensile test, the appropriate
equation would be AL Ao Lo
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What have you learned?