Stamping clearance is the main factor affecting the quality of profile. Only when concave convex die is used; upper and lower cracks can overlap. At this time, the slope of the sheet section is small, relatively flat, the surface is smooth, the burr is small and there is no crack delamination. The influence of the middle gap on the sheet metal is different. When the die gap is too small, the cracks near the edge of the punch enter the compression stress area under the punch and stop developing.

The results show that the crack concave convex die is produced near the punch edge of the material. If they do not overlap, the cross-section material will fracture twice at the distance between the two cracks. A second bright band, double bright band, is produced. Some materials are extruded with burrs on the surface. Or there is no second bright band, but there are intermittent small bright spots on the fracture surface. That is to say, the bright part of the part is too wide and has toothed burr. Its section and burr are shown.

If the die gap is too large, the tensile stress in the material will lead to premature tensile fracture. Therefore, the broad band of fracture surface becomes narrow. When the gap is too large, the cracks do not coincide. The slope of the fracture layer produced by the second crack increases the slope of the fracture layer which appears in the plane. Sometimes, the middle part of the section is obviously concave, and the burr is not only high but also triangular.

In other words, the cross section of the workpiece is rough and round, the light stripe is very small and has long burr. Burr and section. Uneven die gap corresponding to the blanking sheet may also appear too large or too small. That is, the cross section of the workpiece has uneven shallow band or inclined burr on one side.