Basic Theory of Metal Working Machinery's Handbook, 31st Edition
1404
Reduction can be defined as
A A A 0 −
100 f
ψ =
(12) where l f = length at the fracture (in.); l 0 = the original specimen’s gauge length (in.); A 0 = original specimen’s gauge cross-sectional area, (in 2 ); A f = cross-sectional area of the specimen at the fracture, (in 2 ). Note: l f length is measured between the original gauge marks after the pieces of the broken specimen are placed together. Elongation ranges between about 8 and 60 percent for most metals, and typical measure ments for reduction of area range from about 20 to 90 percent. Ductile materials such as thermoplastic and superplastic materials show large deformation before fracture, and of course, exhibit much higher ductility, but brittle materials have little or no ductility. Designing Sheet Metal Parts for Production Sheet metal parts should be designed to satisfy the following criteria: The parts should allow high productivity rates. They should make highly efficient use of the materials involved. The production machines should be easy to service. Machines should be usable by workers with relatively basic skills. Unfortunately, very few product designers concern themselves with suitability of pro duction; their prime concern is usually the function of the part. Design rules for parts to be produced by blanking and punching: Avoid part design with complex configurations. Use minimum dimensions of punched openings relative to material thickness given in Table 1. Use minimum distances between punched opening and rounded radius relative to material thickness given in Table 2. Table 1. Minimal Dimensions of Punched Openings 0 #
b
d
b
b
b
Form of opening
Material
Circle d min = 1.50 T 1.20 T 1.00 T 0.90 T 0.80 T 0.25 T
Square b min = 1.40 T 1.10 T 0.90 T 0.80 T 0.70 T 0.45 T
Rectangular b min =
Oval b min = 1.10 T 0.80 T 0.60 T 0.55 T 0.55 T
Stainless steel
1.20 T 0.90 T 0.70 T 0.60 T 0.60 T 0.35 T
High-carbon steel Medium-carbon steel
Low-carbon steel Brass and copper
Magnesium alloy at 500 ° F 0.30 T Note: With fine punching process, minimal diameter of punched hole is (0.50 - 0.70) T .
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