Materials For Stamped Parts
The surface and internal properties of sheet metal used for stamping have a significant impact on the quality of the finished stamped parts. The requirements for stamping materials are:
① Precise and uniform thickness. Stamping dies are precise with small clearances. Excessive sheet thickness increases deformation forces, causing jamming and even cracking the die; insufficient sheet thickness affects finished product quality and may even lead to tearing during deep drawing.
② Smooth surface, free of blemishes, scars, scratches, and surface cracks. All surface defects will remain on the surface of the finished workpiece. Cracks may propagate deeper and wider during bending, deep drawing, and forming processes, resulting in scrap.
③ Uniform yield strength with no obvious directionality. Anisotropy (see: In the process of deep drawing, flanging, bulging, etc., of sheet metal undergoing plastic deformation, the different timing of yielding in each direction leads to inconsistent plastic deformation, causing uneven deformation, inaccurate forming, and resulting in defective or scrap products.)
④ High uniform elongation. In tensile tests, the elongation of the specimen before the appearance of necking is called the uniform elongation. During deep drawing, the deformation in any area of the sheet metal must not exceed the uniform elongation range of the material; otherwise, uneven deformation will occur.
⑤ Low yield strength ratio. The ratio of the yield strength to the ultimate tensile strength of a material is called the yield strength ratio. A low yield strength ratio not only reduces deformation resistance but also reduces the tendency to wrinkle during deep drawing, reduces springback after bending, and improves the accuracy of bent parts.
⑥ Low work hardening. Work hardening that occurs after cold deformation increases the deformation resistance of the material, making further deformation difficult. Therefore, sheet metal with a low hardening index is generally used. However, materials with a high hardening index have good plastic deformation stability (i.e., more uniform plastic deformation) and are less prone to localized tensile cracking.
