What causes the uneven shape of stamping and stretching parts

In the process of processing stamping and stretching parts, we often encounter the uneven shape of the products, sometimes we can not find a solution after a long time of research. There are many reasons for the unevenness of metal stamping and stretching parts. The main reasons and solutions are as follows:
(1) There is no air hole on the punch. In the stamping process, the air in the workpiece is compressed by the punch and can not be discharged, which makes the shape of the drawing part uneven. This reason is often ignored by many people. The solution is to add air holes on the punch.
(2) The blank is not smooth. The surface of the blank is not smooth, which leads to the surface unevenness of the drawing part. The solution is to replace the material with good surface quality.
(3) The material has a large rebound. The springback of the material is large, resulting in the uneven shape of the drawing part. The solution is to increase annealing or shaping process.
(4) The gap between punch and die is too large. If the gap is too large, the working surface of the die will lose the straightening effect on the workpiece wall, and the workpiece shape will be uneven. Therefore, the die gap should be repaired or replaced with new parts.
(5) The negative deviation of material thickness is too large. If the thickness of the material is too small, the gap between the dies will be relatively large, resulting in uneven shape. It is necessary to change the material with proper thickness.