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.
PIN AND BUSH
CALCULATIONS
NB: The following
calculations allow for 0.25 inches die re-grind allowance. If a greater
allowance is required, reduce pin and bush lengths accordingly.
MAX PIN LENGTH = Shut
height -- 0.5 inches
MAX BUSH LENGTH = Shut
height -- Bottom plate thickness -- 0.75 inches
MIN BUSH LENGTH = Shut
height + Stroke -- Pin length + 0.5 inches
NB: Where min bush length
is greater than max bush length, the bushes leave the pins. In this
instance, the maximum dimension takes preference.
