Auto stamping parts may have typical defects such as wrinkling, cracking, rebound, etc. during the stamping process, and the factors causing stamping defects can be summarized as follows:
The forming limit curve (FLD) is usually used to represent the formability of sheet metal theoretically, in which the strain hardening index n and the thickness hardness index r of metal materials have a significant impact on the curve fitting effect.
In stamping deformation, the higher the strain hardening index n, the greater the deformation allowance, the stronger the material carrying capacity, but the harder the material processing hardening ability, and necking defects are prone to occur. The greater the thickness hardness index r, the better the tensile performance of the material, and the more uniform the overall thickness deformation, making metal sheet has better formability.
Different stamping methods should use different types of dies, and the requirements for die materials are also different. The surface hardness and roughness of the mold will affect the burr defects of the workpiece.
The scratches on the working surface of the mold and the impurities inside the die material will affect the surface quality of the workpiece, causing defects such as drawing and indentation.
The gap between the convex and concave molds has an extremely important influence on the quality of the stamped parts. If the gap is too small, the material between the convex and concave molds will be sheared again, and the section will have longer burrs; if the gap is too large, the bending and stretching of the material will increase, and burrs with a certain thickness will be formed, and the workpiece will produce warpage and deformation. Therefore, the gap between the convex and concave molds should be even and reasonable.
In addition, the radius of the convex and concave mold corners has a significant impact on the quality of the tensile parts. If the radius is too large, the contact area between the sheet metal and the mold will be reduced, that is, the sheet metal is in a suspended state, which is prone to wrinkling defects; if the radius is too small, the squeezing effect and frictional resistance of the sheet metal will increase, and the surface of the workpiece is prone to fracture defects. Therefore, the radius of the convex and concave molds should not be too large or too small.
The process parameters that affect stamping defects mainly include edge pressure, stamping speed, the setting of the blankholder, the use of lubricating oil, and the setting of the forming process.
If the edge pressure is too small and the lubricating oil on the edge ring is too much, the feeding speed will increase, which will cause wrinkling defects of the sheet metal; if the edge pressure is too large and the lubrication condition is not good, the relative sliding between the punch and the material will be reduced, resulting in thinning and rupture of the dangerous cross-section.
Due to the asymmetry of the structure of the large-scale parts, the material flow rate is inconsistent during forming. Therefore, it is necessary to set the blankholder on the edge ring to control the material flow rate in different areas, so that the stamped parts can be uniformly deformed. The stamping process of stamping automotive parts is not fixed. Different manufacturers may provide different process plans for the same part, but they adhere to a basic principle, that is, in the case of no interference in the structure, the production should be processed with the least steps as possible.
In addition, with the development of computer technology, CAE analysis software can be used to numerically simulate the stamping process, optimize the process and parameters, and reduce stamping process defects and production costs.
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