BLANKING

Where F(b) = Blanking force (kN), P = Perimeter of blank (mm), S(s) = Shear strength (MPa), c = a constant for impact loadings.

Grinding a shear angle on a punch minimises the shock load on a press and gives a quieter punch operation. For zero shear, when s = 0, c = 1.25. For part shear, when s = 0.3t, c = 1.0. For full shear, when s = t, c = 0.75. (NB: on a small diameter, multi-punch set-up, staggering the length of punches gives a similar effect on shock loads.) e.g. 150mm diameter blank in 3mm mild steel with part shear on punch gives:

DRAWING

 

Where F(d) = Drawing force (kN), P = Perimeter of draw (mm), S(y) = Yield strength (MPa), b = a constant for non-draw areas, d = a factor to be used when using a die cushion.

When drawing circles, b = 1.0. When drawing irregular forms, corners are non-draw areas and b should be reduced by 0.1 for each corner where the radius is less than 0.3 times the length of the shortest adjacent side. e.g. 150 x 50 pan with 10mm radius corners in 1.6mm mild steel.

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