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ME 482 - Manufactur ing Systems

Introduction To

Manufacturing Systemsby

Ed Red

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What we will cover

L

Do Dfp

Fundamental metal forming and removal technologies

Flexible manufacturing systems

Electronics manufacturing (1/3rd of all manufacturing)Electronics production machines and processes

Process Models

- Force- Power- Wear- Production rate- Etc.

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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):

se

e

Elastic region

Plastic region

0.2% offset

Ultimate strength

Yield strength

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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 90,000MPa 70 600

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Elastic region

Plastic region

Material Behavior in Metal Forming

True Stress and Strain (used by manufacturing engineers):

True stress s = F/A

True straine

= dL/L = ln(L/Lo)

sStart of necking

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Material Behavior in Metal Forming

Why do engineering designers base their designon 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 30,000 210 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

Determine 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?