Busbar punching

Punching is where hole quality and tooling cost are both decided, and the variable that governs each is the same one: clearance between punch and die. Set it as a percentage of material thickness per side — commonly around ten percent for copper, within a working range of roughly five to twelve percent. Too little and the fracture lines from the punch and the die never meet, so the material tears instead of shearing cleanly, the edge shows a secondary shear band, and the punch wears fast. Too much and rollover grows and the slug tends to pull back out of the die on retraction. Punch force is the hole perimeter multiplied by material thickness multiplied by the material's shear strength, so a shaped hole in thick, hard bar can demand several times what a small round hole in annealed copper needs. Size the machine for the worst case in the drawing set, not the average.