Since bent metal is longer after bending, its increased length, generally of concern to the product designer, may also have to be considered by the die designer if the length tolerance of the bent part is critical. The length of bent metal may be calculated from the equation: B=A/360*2π, where
B—bend allowance, in(mm) (along neutral axis)
Ri—inside radius of bend, in (mm)
t—metal thickness, in(mm)
K—0.33 when Ri is less than 2t and is 0.50 when Ri is more than 2t.
Two bending methods are commonly made use of in press tools. V bending and edge bending:
1. Metal sheet or strip, supported by a V block, is forced by a wedge-shaped punch into the block. This method, termed V bending, produces a bend having an included angle which may be acute, obtuse, or of 90￮. friction between a spring-loaded knurled pin in the vee of a die and the part will prevent or reduce side creep of the part during its bending.
2. Edge bending is cantilever loading of a beam. The bending punch 1 forces the metal against the supporting die.
3. The bend axis is parallel to the edge of the die. The work-piece is clamped to the die block by a spring-loaded pad 2 before the punch contacts the workpiece to prevent its movement during downward travel of the punch.