Blanking is a basic sheet metal stamping process that uses molds to separate materials. It can be directly made into flat parts or prepare blanks for other stamping processes such as bending, deep drawing, forming. Besides, incision and trimming can also be made on formed stamping parts.
Blanking is widely used in industries such as automobiles, household appliances, electronics, instrumentation, machinery, railways, communications, chemicals, light industry, textiles, and aerospace. The blanking process accounts for about 50% to 60% of the entire stamping process.
The basic process is blanking and punching, which not only can process parts but also can process stamping process parts.
1. The shape and size of the blanking parts are as simple as possible to minimize the waste during layout.
2. The shape and inner hole of the blanking parts should avoid sharp corners. There should be arc links at the links of straight lines or curves, and the arc radius R≥1.5t (t is the plate thickness).
3. Blanking parts of precision sheet metal components should avoid narrow cantilevers and slots. The depth and width of the convex and concave recesses of the blanking parts of the sheet metal pressing process should generally not be less than 151 (t is the thickness of the material), and at the same time, avoid narrow and long interfaces and too narrow grooves to enhance the die edge strength.
4. For punching, round holes should be used first, and punching has a minimum size requirement.
5. Blanking space and hole margin is important because the minimum distance between the punching edge of the part and the shape is limited depending on the shape of the part and the hole. When the edge of the punching hole is not parallel to the shape of the part, the minimum distance should not be less than the thickness t of the material, and not less than 1.5t when it is parallel.
6. When punching the bending parts and deep drawing parts, keep a certain distance between the hole wall and the straight arm.
7. The hole margins on the bending parts should be noted. One should punch holes first and then bend, the hole position is outside the bending deformation area, to avoid the hole deformation when bending.
8. Add sheet metal stamping process positioning holes in the design. In order to ensure the accurate positioning of the blank in the mold and prevent the blank from shifting during bending, the process positioning holes should be added in advance during the design, especially for multiple bending forming. All parts must be positioned based on the process hole position to reduce accumulated errors and ensure product quality.
When the clearance is normal and the cutting edge is sharp, the blanking deformation process can be divided into three stages:
1. In the elastic deformation stage, the internal material stress in the deformation zone is less than the yield stress.
2. In the plastic deformation stage, the internal material stress in the deformation zone is greater than the yield stress. There is a gap between the convex and concave molds, and the deformation is complicated. It is not pure plastic shear deformation. It is also accompanied by bending, stretching, and compression and other deformations of the convex and concave molds.
3. The internal material stress in the deformation zone in the fracture separation stage is greater than the strength limit.
The cracks first occur on the side near the edge of the die, then on the side near the edge of the punch, which causes the upper and lower cracks to meet and finally to separate the material.
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