How to choose precision stamping raw materials

At present, the materials available for stamping are not only low carbon steel, but also stainless steel, aluminium and aluminium alloys, copper and copper alloys. Materials with a carbon content of <0.25% and a tensile strength of less than 650 N/mm² are generally used. Examples are cold rolled steel SPCC (JIS) or 1010 (SAE).

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The 4 requirements for precision metal stamping materials mainly include the following.
1. Chemical composition of the material: Generally speaking, the lower the carbon content of the steel, the lower the content of impurities, the better the plasticity and the lower the hardness.
2. Surface quality of the material: the material for stamping parts is mostly steel plate, commonly used as thin plate.
When stamping dies work, they have to bear impact, vibration, friction, high pressure and deep drawing, bending and twisting, and even work under higher temperatures, so the working conditions are complicated and prone to wear, fatigue, fracture and deformation; therefore, the requirements for the materials of the working parts of the dies are higher than those of ordinary parts. The country has certain regulations and requirements for the surface quality of steel plates. The material’s surface must be smooth and free from scratches, impurities, porosity and shrinkage; there is no delamination in the cross-section of the material and no obvious damage to the mechanical properties; the material’s surface should be free from rust, oxide and other adhesions. In precision stamping, materials with good surface quality can obtain smooth surfaces and high-quality stamped parts. Still, they are not easy to break and damage the die during the deformation process.
3. Microstructure: The mechanical properties of metal materials depend not only on their chemical composition but also on their microstructure. Generally speaking, the microstructure of a metal is very fine, but the plasticity is very high, which facilitates the deformation of the material in the stamping process. However, if the microstructure of the metal is too fine, the strength and hardness of the material will increase.
4. Thickness tolerance: In the precision stamping process, the requirements for thickness tolerance are relatively strict. In precision stamping and forming, high pressure and even damage to the parts can occur.

 

How to choose metal stamping materials for your products
For any kind of metal stamping, the material chosen should be able to form a stable and qualified product without cracking or wrinkling according to the requirements of the stamping process, which is a basic and very important requirement for material selection.
1. Reasonable selection of materials according to the requirements for the use of metal stamping parts
The material selected should enable the stamped part to work properly in the machine or component and to have a certain service life. For this reason, the selected material should meet the requirements of strength, stiffness, toughness, corrosion resistance and heat resistance following the conditions of use of the stamped parts.
2, reasonable selection of materials according to the requirements of the stamping process
 For any kind of metal stamping parts, the selected material should be able to form a qualified product without cracking or wrinkling stably according to the requirements of the stamping process. For this reason, the following methods can be used to reasonably select the material.
 (1) Test punching. Based on previous production experience and possible conditions, select several types of sheet material that can meet the requirements for the use of stamped parts for test punching, and then select the one that does not crack or wrinkle and has a low scrap rate. The results of this method are more intuitive but with a greater degree of blindness.
 (2) Analysis and comparison. Based on the analysis of the nature of stamping deformation, the degree of maximum deformation during stamping and forming and the ultimate degree of deformation allowed by the sheet stamping and forming performance are compared and used as a basis for selecting a sheet suitable for the requirements of the stamping process of the part.
 In addition, there are cold-rolled and hot-rolled differences in the same grade or the same thickness of the plate. Compared with hot-rolled plates, cold-rolled plates have accurate dimensions, small deviations, few surface defects, bright, dense internal organization and better stamping performance.
  3, according to the economic requirements of reasonable selection of materials
 The materials selected should be as low as possible, convenient in origin and economical to reduce the cost of the stamped parts, provided that they meet the requirements of the performance and stamping process.
The material’s surface should be smooth and flat, free from delamination and mechanical damage, rust spots, oxidation skin and other adhesions. The material should have good formability, rigidity, extensibility, dent resistance, corrosion resistance and weldability and other process properties. The thickness tolerance of the material should be in line with the standards stipulated by the national Jia. The material should have good adaptability to mechanical bonding and further processing such as welding, painting, plating, machining and riveting etc. 1. Tensile parts should not be made of materials with a small strain hardening index.
The strain hardening index has a very close relationship with the forming performance of the sheet metal. According to the plastic deformation limit theory, the maximum elongation strain when the sheet is stretched centrally is twice as high as when it is stretched uniaxially. Under normal conditions, the material will rupture immediately after the occurrence of necking concentration. Therefore, the greater the strain hardening index of the material, the greater the resistance of the material to local fracture, the more uniform the plastic strain distribution tends to be and the lower the peak strain. Therefore, it is not advisable to use materials with a small strain hardening index in moulded parts where elongation is the main concern.
2. Compression forming process should not use materials with poor stability resistance
In compression forming, the deformation zone is mainly reached by the compressive stress and compressive strain to withstand the compressive deformation. The sheet under the action of compressive stress is easy to instability and wrinkle. In order to improve the stability of plastic deformation, it is not advisable to choose materials with poor resistance to instability.
3. Poorly plasticised materials should not be used in the drawing process
Materials with low elongation should not be used in the stretching process. The better the plasticity of the material, the higher its uniform elongation, which means stretch forms between stable and uniform deformation.
4. Hardened materials should not be used in the spinning process
Commonly spun materials are mainly pure aluminium, mild steel and stainless steel, of which mild steel and stainless steel account for more than 60%. For common spinning, soft materials with good plasticity, low yield point, few impurities and uniform structure should be used.
5. No high strength, low-plasticity materials should be used in the cold stamping process
High-strength, low-plasticity materials should not be used in the cold stamping process to avoid increased resistance to deformation and cracking. The requirements for materials for cold stamping and other volume forming are that the material should have high plasticity, low yield point and low work-hardening sensitivity. Commonly used cold stamping materials are pure aluminium and aluminium alloys, copper and copper alloys, low carbon steel, medium carbon steel, low alloy steel, etc. Products stamped with these materials have a smooth surface, dimensional accuracy and can withstand high pressures. A single plastic deformation punches out products with complex shapes.
6. No highly elastic materials should be used in the bending process
Stamping and bending steel need to have good plasticity, low yield strength and low elasticity. Steel with good plasticity in the bending process is not easy to bend and crack. It is low yield, high strength, and low elasticity of steel; bending after forming the rebound deformation is small, and it is easy to obtain the exact shape of the bend.
7. elongation forming should not use poor plasticity materials
In the stamping process, flaring, reaming, bulging, bending, outward turning of the tube, and part of the stretching belongs to the extension type deformation. As the deformation zone is mainly subject to tensile deformation by normal stress and normal strain, the material in the deformation zone is susceptible to excessive elongation. When this elongation exceeds the ultimate elongation of the material, it is prone to fracture and is therefore unsuitable for using less plastic materials in the elongation formation process.

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