In the production of stamping parts, choosing the right material is the most basic work. Only by choosing the right material can the ideal product be produced in the subsequent processing. Most of the stamping plants now know very little about how to choose materials. The selection of stamping materials mainly has the following principles:
First, the bending process should not use highly elastic materials
Pressed and bent steel needs to have good plasticity, lower yield strength and lower elasticity. Steel with good plasticity is not easy to bend and crack when bending; it has low yield. The steel material with low strength and low elasticity has little springback deformation after bending and forming, and it is easy to obtain a precise bending shape. In the steel, low-carbon steel and brass and other well-shaped materials are easy to bend, and high-elastic materials (such as high-carbon steel, stainless steel, spring steel) are difficult to obtain accurate dimensions due to large springback during bending Bend shape. The higher the yield strength of the material, the harder and more elastic the material, and the greater the amount of springback, the worse the dimensional accuracy of the bending part. Therefore, it is not suitable to use such highly elastic materials in the bending process.
Second, the deep drawing process should not use materials with poor plasticity
The stretching process should not use materials with low material elongation. The better the plasticity of the material, especially the higher the uniform elongation, it means that the stretch forming is performed between stable and uniform deformation. The later the necking occurs, the stretch forming is less likely to crack, so the tensile properties Just fine. In the stretching process, the more difficult it is to deform in the thickness direction, the less likely the punch fillet area (here is the dangerous section of tensile deformation) to thin and break, so the better the tensile properties.
Third, ordinary spinning should not use hardened materials
The common spinning materials are mostly pure aluminum, low carbon steel and stainless steel, and the proportion of low carbon steel and stainless steel exceeds 60%. Normal spinning should use soft materials with good plasticity, low yield point, few impurities and uniform organization. Pure aluminum and 3A21 aluminum alloy have the best spinability, 2A12 duralumin and low carbon steel are good, and 5A03 and 5A06 are poor. Stainless steel is best heated and spun.
Fourth, the elongation forming process should not use materials with poor plasticity
In the stamping process, flaring, reaming, bulging, bending, eversion tube, and partial stretching belong to the type of elongation deformation; stretching, diameter reduction, inside turning tube, and tube blank upsetting belong to compression type forming. Elongation forming Because the deformation zone is mainly subjected to tensile deformation of positive stress and positive strain properties, the material in the deformation zone is prone to excessive elongation. When this elongation exceeds the material’s ultimate elongation, it is easy to crack. Therefore, materials with poor plasticity should not be used in the elongation forming process.
Fifth, it is not appropriate to use materials with poor resistance to instability in the compression forming process
In compression forming, the deformation zone is mainly subjected to compression deformation of compressive stress and compressive strain properties. Under the action of compressive stress, the sheet material is prone to instability and wrinkling. Therefore, in order to improve the stability of plastic deformation, it is not appropriate to choose materials with poor anti-stability.
Sixth, it is not suitable to use materials with small strain hardening index in the forming parts that mainly take elongation
The strain hardening index is closely related to the sheet metal stamping performance. According to the theory of plastic deformation limit, when uniaxially stretched, the maximum elongation strain when the sheet is subjected to concentrated necking is 2 times. In general, the material will rupture soon after the concentrated necking occurs. Therefore, the greater the strain hardening index of the material, the stronger the local resistance to cracking, the plastic strain distribution tends to be uniform, and the peak strain value is low The overall forming limit of sheet metal forming, therefore, it is not appropriate to use materials with a small strain hardening index in forming parts that are mainly elongated.
Seven, cold extrusion process should not use high-strength, low plastic materials
The cold extrusion process should not use high-strength, low-plasticity materials, so as not to increase deformation resistance and cracks. The requirements of cold extrusion equal volume forming on the material are: the material should have high plasticity, low yield point and low work hardening sensitivity. Commonly used cold extrusion materials are pure aluminum and aluminum alloys, copper and copper alloys, low carbon steel, medium carbon steel, low alloy steel, etc. The extruded products of this kind of material have a smooth surface and a dimensional accuracy, and can withstand large plastic deformation at once, extruding products with complex shapes. On the contrary, like high carbon steel (45-70 steel), high alloy steel (40Cr), carbon tool steel, etc., the extrusion force is large and the forming is difficult. Warm extrusion or hot extrusion should be used.