Reasons and measures for cracking and wrinkling of stamped parts

The occurrence of cracking and wrinkling problems in deep drawing stamping parts not only easily leads to the scrapping of stamping parts in the production process, waste of raw materials, and increased production costs, but also makes it easier for welding points to twist and crack during the welding process. Therefore, solving the cracking and wrinkling problems of deep drawn stamping parts is of great significance for the production of deep drawn stamping parts. Based on practical work experience, a summary and analysis were conducted on the methods for controlling cracking and wrinkling problems in deep drawn stamping parts.

1、 Reasons for cracking and wrinkling of deep drawn stamping parts

Specifically, the reasons for cracking and wrinkling of deep drawn stamping parts mainly include the following aspects.

1、 The stretching of deep drawn stamping parts is too deep, causing the sheet metal to flow too quickly during the feeding process, resulting in cracking and wrinkling., Related to stamping dies, stamping dies have concave convex molds, and the large angle of the concave mold makes it impossible for the convex mold to press down on the raw material, resulting in relative motion and uneven stretching of the sheet metal during the flow process. Thirdly, deep drawing stamping parts have a relatively large drawing process, and drawing ribs are rarely or not used in the stamping forming process. This is mainly done to ensure sufficient blank material during the drawing forming process. So, the flow of the blank material in deep drawn stamping parts is mainly controlled by the frictional force of the pressure. This leads to problems such as cracking and wrinkling in the production process of deep hand stamping parts. Fourthly, the pressure on the crossbar is too low, resulting in uneven forming of the stamped parts and uneven force distribution.

2、 Measures to control cracking and wrinkling of deep drawn stamping parts

In summary, the method to control cracking and wrinkling of deep drawn stamping parts is to control the flow speed of the sheet metal. Because ultimately, the cracking of deep drawn stamping parts is caused by the slow flow of the sheet metal during stretching, while wrinkling is caused by the fast flow of the sheet metal during stretching. From this, it can be seen that by controlling the sheet metal and preventing relative motion between the sheet metal and the mold, the problem of cracking and wrinkling in deep drawn stamping parts can be effectively controlled. Specifically, efforts should be focused on the following aspects.

1. Adjust the gap between the pressing surfaces

Through practical experience, it has been found that it is very difficult to control the compression force well. Therefore, adjusting the stretching gap is adopted to prevent changes in material stress and deformation caused by changes in material thickness.

Generally speaking, there are two main methods to adjust the gap between the pressing surfaces. A type of pressure material with tight gaps inside and loose gaps outside. In the straight bending deformation zone and extended deformation zone of the concave die mouth, it is allowed for the pressing surface to be tight inside and loose outside. Because the thickness of the sheet metal remains constant or decreases in these two regions, the gap between the pressing surfaces increases or remains constant, which relatively reduces the pressing force. When the sheet metal flows through the tight zone, the squeezing effect of the pressing surface on the sheet metal weakens. The method of adjusting the gap between the inner tight and outer loose pressing surfaces can effectively prevent wrinkling.

The gap between the material surface is loose inside and tight outside. This principle is mainly applied in the compression deformation zone, where the material is in a stress state of radial tension and tangential compression. The blank undergoes compression deformation in the circumferential direction. As the material flows, the thickness of the material tends to increase, which reduces the gap between the pressing surfaces and increases the feeding resistance. The material is prone to rupture under tensile stress. Therefore, when adjusting the gap between the pressing surfaces of the mold, the method of loosening inside and tightening outside should be adopted, as the increase in material thickness has an adverse effect on material deformation.

2. Adjust the magnitude of the edge pressure

Adjusting the magnitude of the edge pressure mainly relies on practical operational experience to make a comprehensive judgment. Generally speaking, when wrinkles are evenly generated around the workpiece, the operator should be very careful, which indicates that the pressure of the material is not enough. Wrinkles can be gradually increased by gradually increasing the pressure of the material. On the contrary, when excessive pressing force is found, the size of the pressing force should be correspondingly reduced, otherwise the sheet metal is prone to cracking. In short, the adjustment of edge pressure should be based on the characteristics of the stamped part itself. The magnitude of edge pressure varies for different stamped parts or different parts of the same stamped part. Especially for automobiles, there are many complex stretching parts with different deformations due to structural asymmetry. If the same amount of edge pressure is applied, the resistance around the material will be the same, resulting in wrinkles in the parts with small deformation and cracking in the parts with large deformation. Therefore, it is recommended to use a double action stretching press. As long as the operator understands the working principle and structure of the press, they can adjust the edge pressing force according to the deformation of the stamped parts, so as to deeply stretch the stamped parts and prevent cracking and wrinkling problems.