Shearing

The purpose of shearing is to achieve controlled separation of the part from the scrap, this includes operations, e.g. slitting, separate parts (cut-off, parting), cut out a part (blanking), create a hole (punching), produce notches, and so forth. The basic shearing process relies on the controlled production of cracks propagating from both sides of the sheet. With proper clearance between punch and die, the cracks meet but the cut surface is slightly inclined and rough.

Tool wear results in the formation of a ragged burr that causes stress concentrations and may lead to fracture during further forming or in service. In fine blanking, crack formation is suppressed by the hydrostatic pressure generated by impingement rings, and a smooth, perpendicular surface, suitable as the contact surface on a net shape part, is produced, but at higher die and equipment cost.