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The stamping process can be divided into two categories: separation process and forming process. The separation process includes blanking, punching, trimming, etc., while the forming process includes stretching, bending, flanging, etc. Propose detailed preventive measures and solutions for possible wrinkling, cracking, and rebound defects in each process.
1. Wrinkling
The fundamental cause of wrinkling defects is due to the compression of the sheet metal, and when the main and secondary stresses in the plane direction reach a certain level, the thickness direction becomes unstable. According to the different causes of wrinkle formation, it can be divided into two types. One is the accumulation of wrinkles caused by excessive material entering the cavity of the concave mold; The second type is instability and wrinkling caused by instability in the thickness direction of the sheet metal or uneven tensile stress. In order to address this defect, the specific solutions are as follows: (1) From the perspective of product design: minimize the flanging height as much as possible; Connect the areas with sharp changes in shape in a smooth state; For areas where the product is prone to wrinkling, appropriate suction shapes can be added; (2) Starting from the design of stamping process: increase the blank holding force and control the feeding speed; Add circular or square stretching ribs to the process supplement; Increase the forming process within a reasonable range; (3) For the selection of stamping materials: under the condition of meeting product performance, for some parts that are prone to wrinkling, materials with good formability should be selected.
2. Cracking
The fundamental reason for the formation of cracking defects is that the strain exceeds it during the stretching process of the material, which is more intuitively manifested as visible cracks on the surface of the workpiece. Usually, it can be divided into three types: one is caused by insufficient tensile strength of the material, and the reason for the fracture is generally due to excessive local force at the rounded corners of the convex and concave molds; The second is due to insufficient deformation of the material, such as cracking at the sharp point; Three types of cracks are caused by impurities in the material. Therefore, in order to prevent fracture defects, the fundamental measure is to reduce stress concentration. The specific plan is as follows: (1) Choose a reasonable billet size and shape; (2) Adjust the stretching bar parameters to prevent cracking due to excessive expansion force; (3) Increase process cuts, ensure reasonable material flow, and achieve uniform deformation; (4) Change lubrication conditions, reduce friction, and increase feed speed; (5) Reduce the blank holding force or use a variable blank holding force to control the feed resistance; (6) Using materials with good ductility and formability to reduce cracks.
3. Rebound
The vast majority of stamping parts will produce rebound defects, and the root cause of rebound can be summarized as follows: after stamping deformation, the material is elastically loaded, resulting in local or overall deformation. Stamping materials, pressure levels, and mold status can all affect rebound. For rebound defects, the solution is as follows (1) Compensation method, that is, based on the size of the springback of the stamped part after bending forming, a slope equal to the springback of the workpiece is pre made on the mold to compensate for the springback after forming. The amount of springback required for compensation in this method is mainly determined by manual experience estimation or CAE numerical simulation analysis results; (2) Pull bending method: Apply tensile force while bending the sheet metal, in order to make the stress distribution inside the sheet metal more uniform, thereby reducing the amount of rebound; (3) Local pressure method: