The surface and intrinsic properties of the sheet metal used for stamping have a great influence on the quality of the stamped product. The requirements for stamping materials are:
①The thickness is precise and uniform. The stamping die is precise and the gap is small. If the thickness of the sheet is too large, the deformation force will be increased, which will cause the material to jam, and even the die will burst. If the sheet is too thin, the quality of the finished product will be affected, and even cracking will occur during deep drawing.
②Smooth surface, no spots, no scars, no scratches, no surface cracks, etc. All surface defects will remain on the surface of the finished workpiece, and crack defects may expand to deep and wide in the process of bending, drawing, and forming, resulting in waste.
③ The yield strength is uniform and has no obvious directionality. Anisotropy (see the plastic deformation of sheet metal in the stamping process of deep drawing, flanging, bulging, etc., due to the emergence of yield in each direction, the amount of plastic deformation is inconsistent, which will cause uneven deformation and inaccurate forming. defective or scrap.
④High uniform elongation. In the tensile test, the elongation before the necking phenomenon of the sample begins to appear is called the uniform elongation. During deep drawing, the deformation of any area of the sheet cannot exceed the uniform extension of the material, otherwise uneven deformation will occur.
⑤ The yield strength ratio is low. The ratio of the yield limit to the strength limit of a material is called the yield-strength ratio. A low yield-to-strength ratio can not only reduce the deformation resistance, but also reduce the tendency of wrinkling during deep drawing, reduce the amount of springback after bending, and improve the accuracy of bending parts.
⑥ Low work hardening. The work hardening that occurs after cold deformation will increase the deformation resistance of the material, making it difficult to continue to deform, so a plate with a low hardening index is generally used. However, materials with high hardening index have good plastic deformation stability (that is, plastic deformation is more uniform), and local cracking is not easy to occur.
In actual production, technical tests similar to the stamping process are often used, such as deep drawing performance tests, bulging performance tests, etc. to test the stamping performance of materials to ensure the quality of finished products and high pass rate.
