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Stamping is mainly classified into two categories: separation process and forming process. The separation process, also known as blanking, aims to separate the stamped parts of automotive components from the sheet metal along the contour line, while also separating sections with quality requirements. The purpose of the forming process is to cause plastic deformation of the sheet metal without damage, so that the workpiece has the required shape and size. In practical production, many processes are often applied to workpieces. Blanking, bending, shearing, stretching, bulging, spinning, and straightening are the main stamping processes.
For automotive panels, surface quality is particularly important. In addition to considering the general process characteristics of vehicle body metal stamping parts, the surface should not have defects such as ripples, wrinkles, dents, scratches, and indentations. The edge line should be clear and straight, and the curve should be smooth and transition evenly. In addition, automotive panels also require high dimensional accuracy to meet the accuracy requirements of welding and assembly. In actual mold testing or production processes, many defects are often encountered. We mainly analyze the following defects.
1. Whispering sound
Burr is a common problem in the shearing section. If high and fine burrs appear around the workpiece, the main reason is the small gap between the convex and concave molds or the wear of the cutting edge, which can be solved by adjusting the gap or grinding the convex and concave molds. If there are high and thick burrs around the parts, it is because the gap is too large, so it is necessary to increase the gap between the male and female molds.
2. Wrinkling
The flange wrinkling and simple wall wrinkling of drawn parts are mainly caused by the compression deformation of the sheet metal during the drawing process. During the stretching process, due to the tangential compressive stress of the flange material, when the compressive stress is large enough, the plate will become tangential arched due to instability. This continuous bending with waves around the flange is called wrinkling. Wrinkling is usually achieved by increasing the radial tensile stress in the plate. When wrinkles are evenly formed around the parts, the pressure should be insufficient and gradually increased to wrinkle.
When stretching conical and hemispherical parts, most materials are in a suspended state at the beginning of stretching, which can easily lead to sidewall wrinkling. Therefore, in addition to increasing the blank holder force, it is also necessary to increase the radial tensile stress and wrinkling of the sheet by adding tensile ribs. Add stretching ribs at appropriate locations. At the beginning of stretching, the material around the sheet is bent by the stretching ribs. The stretching ribs control the resistance of various parts of the sheet to flow into the mold, which increases the radial tensile stress of the sheet. By continuously changing the position, quantity, fillet radius, and height of the stretching ribs, radial tensile stress can be adjusted to reduce or avoid part wrinkling. You can limit wrinkle resistance by pressing on the edge ring.
When designing drawing parts, if there is excess metal in the parts with sharp changes in shape, the material is prone to flow and may cause wrinkling. It is necessary to consider adding ribs in the process supplement of the part to allow excess metal to flow into the ribs during deep drawing, fully absorbing excess material and preventing wrinkling.
In addition, reducing the degree of tensile deformation and increasing the thickness of the billet can also reduce the trend of wrinkling. 3. Rupture
It is the main manifestation of tensile instability in sheet metal stamping. When the tensile deformation force is greater than the actual tensile strength of the material in the force transfer zone