To make an estimation of the force needed during bending, we pay attention not only to the bend length, plate thickness, die width and tensile strength, but also the changing moment arm during bending. The peak load is assumed to be reached at a bend opening angle of 120° with normal friction (no lubrication). Trial tests are always recommended.
P = Bend force, tons(metric)
t = Plate thickness, mm
W = Die width, mm (figure 1)
b = Bend length, mm
Rm = Tensile strength, MPa (table 1)
Rd = Die entry radius, mm
Rp = Punch radius, mm
The SSAB Bending Formula© is verified by tests for 90° bends, see figure 5.