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Geregistreerd op: 03 Mei 2021
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 Geplaatst: 01-06-2021 06:35:36 Onderwerp: What are the causes for cracking of deep drawn stamping |
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What are the causes for cracking of deep drawn stamping
The elongation ability of stainless steel is small, the elastic modulus E is larger, and the hardening index is higher. The cracking of the SS material sometimes occurs in drawing process e.g in course of deformation, sometimes it happens immediately after the part is withdrawn from the dies. Sometimes it occurs when the drawing parts are impacted or vibrated in the deformation process. And sometimes it happens after a period of time storage of the finished tooling or in the course of using of the dies.To get more news about deep draw metal stamping, you can visit tenral.com official website.
Austenitic stainless steel has a high cold hardening index (0.34% for SS). Austenitic stainless steel is a meta-stable type, which will undergo transformation during deformation thus induce martensitic phase. The martensite phase is brittle, and easy to crack. In the course of plasticity deformation, with the increase of extension, the martensitic content will then increase, the residual stress will all be increased. The relationship between residual stress and martensite content is, the higher the content of induced martensite phase, the greater the residual stress, and the easier cracking is ocurring during processing.
The main reason for all scratches on the surface of stainless steel drawing parts is due to the relative movement of the workpiece and the surface of the die, which, under certain pressure, results in the direct friction between the material and the surface of the die. In addition, the heat produced during the process is also a reason, it makes the raw material and deposited metal chips cling to the surface of the die, resulting in scratches on the surface of the workpiece.
(1) choose the most appropriate stainless steel material: in austenitic stainless steel, the commonly used materials are 1Cr18Ni9Ti and 0Cr18Ni9Ti. During drawing, 1Cr18Ni9Ti is more stable than 0Cr18Ni9Ti and has good cracking resistance. Therefore, 1Cr18Ni9Ti materials should be selected as far as possible.
(2) Choose the correct die material. In the deep drawing process, Stainless steel will be hardened greatly, producing lots of hard metal spots, resulting in adhesion, so it will induce scratching and wear between workpiece and die surface, so the SS should not be chosen for the dies. It has been proved that copper based alloy die can eliminate surface wearing, scratch and reduce a damage rate of SS parts. Another kind of material is high aluminum copper based alloy die material (containing aluminum 13Wtt to 16W t), this kind of material has little solubility with SUS304 stainless steel, the drawing parts do not stick the dies, it is easy not o produce scratches on the parts surface, so the polishing cost of products is low. It has been successfully applied in the field of stainless steel drawing. However, due to the low hardness of the mould, 40HRC (45HRC) is often used to produce products with relatively low thickness t / D. Generally, after 1500 pieces, it is prompted to produce radial edges at the corner R on the surface of the die. Silicon nitride ceramics (Si3N4) has become an important engineering material, especially the reactive sintering silicon nitride ceramics. It has good mechanical properties at high and low temperature, heat resistance impact and chemical stability, and can be easily made into parts with complex shapes. The high hardness, high wear resistance and high chemical stability of ceramic materials can be utilized. So, instead of metal dies, the reactive sintering silicon nitride mould is used to produce SUS304 stainless steel parts. |
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