In the design of automobile body stamping parts, the double-flanging shape is a very common design structure, which plays the role of increasing the matching welding lap surface of the parts and improving the strength of the parts. However, in the actual forming process of stamping parts, the two flanging structures often have flanging wrinkles, flanging overlapping materials, and flanging cracks, which cause the quality of the parts to decline. When the stamping parts of some key parts of the automobile body have the above problems, the strength of the body will be reduced, and even the safety of the occupants will be endangered.

In the design of stamping parts, there are mainly three types of flanging structures usually used: the edge flanging of the ordinary flat part of the workpiece; the edge of the workpiece is bent at the same time and the edges on both sides are turned inward; the edge of the workpiece is bent at the same time and the edges on both sides are both facing Eversion.

For the bending and inward flanging structure, the forming process we usually adopt is first bending and forming, and then flange surface flanging and forming. The common part defect is that the second flanging causes the flange surface to wrinkle.

The bending and outward flanging structure usually has two forming methods: one is the post-drawing flanging process. The parts using this process are prone to flanging and wrinkling defects on the flange surface of the back flanging ; Another forming method is the first flanging and then the second bending forming process. The stamping parts using this process are prone to cracking defects on the flange surface of the first flanging.

There are many reasons for the cracking of stamping parts, but the root cause is that the stretching degree of the cracked part exceeds the strength limit of the material when it is formed, that is, the stretching amount of the material flowing during the forming process exceeds the maximum stretching rate allowed by the material.

For raw materials used in stamping production, there is no material stretching. When bending or flanging forming, the material close to the punch surface of the mold is usually not stretched. Therefore, for the structure of two flanging, when analyzing the risk of flanging edge cracking, only the material pulling of the flanging edge needs to be considered. Whether the elongation exceeds the maximum elongation of the selected material. To analyze whether the flanging edge of the stamping part is cracked, it is only necessary to calculate whether the analysis stretch exceeds the maximum stretch rate allowed by the material.

In the actual product part design process, the flange face flanging angle θ2 is related to the matching relationship between the parts, and the feasibility of adjustment during design is very small. The value of R angle R2 of flange surface flanging is required to be as small as possible. When the value of R2 minus material thickness is about 2～5mm, the flanging requirement can basically be met; and the smaller the value of R2, the flange surface can be made The larger the effective matching area, the higher the quality of product matching.

Combining the calculation formula, it can be known that to reduce the tensile rate δ value of the material during the two flanging, a feasible design control measure for stamping parts is to reduce the length of the material edge at the flanging part of the flange surface, that is, to reduce the h value. And increase the bending R angle, that is, increase the value of R1, but increasing the bending R angle is easy to cause the rebound defect of the stamping parts.