| Recently, with the concept of lightweight being put forward, high strength steel and light material are widely used. Meanwhile, the study on their compacting mechanism, new process and new technique are evolving rapidly, which put forward higher demand on forming equipment. With characteristics of flexibility, intellectualization and high machining accuracy, servo press can effectively increase forming property of products, optimize technology and comprehensively improve the quality of products. At room temperature, the ability of deformation for 304 stainless steel needed to be strengthened, because its deformation needs prodigious load and has some shortcomings, such as cracking, wrinkling and etc, thus leading to instability of the dimension and shape of parts. And the traditional cold stamping is hard to achieve, therefore, hot stamping is an advanced forming technology to solve the above problems. This paper chooses 304 stainless steel with thickness of 0.28 mm as the research object, and studies the stamping process of 304 stainless steel by tensile test, numerical simulation and cold and hot stamping experiment respectively.Initially, AG-25 TA electronic universal testing machine is selected to conduct high-temperature tensile test, in order to gain the mechanical properties of 304 stainless steel at different temperatures. And, based on the relationship between load and displacement, the flow stress curve is drawn, which provided reliable experiment parameters for numerical simulation. Then, high-temperature rheological behavior in the process of hot deformation for 304 stainless steel is studied in combination with microstructure. The results prove that as temperature rises, intensity of 304 stainless steel reduces and plasticity enhances; when the strain is below 2.5%, with the same deformation, stress needed to material deformation at room temperature is far higher than that during the heating, which indicates that as temperature rises appropriately, the plasticity of this material improves considerably. In addition, the fracture morphology is analyzed, the result shows that when the temperature reaches 600°C, the grain boundary clearly weakens, the breakage morphology decreases, and intergranular fracture is its character.The finite element analysis software DYNAFORM is employed to cold stamping simulation analysis of 304 stainless steel, thus determining the forming limiting size and best process parameters for 304 stainless steel. On the basis of stress strain curve obtained from above experiments, the material model is established and used to analyze thermal coupling in the hot stamping forming process. The stress strain and variation of the temperature distribution are gained. Moreover, impacts of such technical parameters as initial temperature of sheet, blank holder force and punch velocity on 304 stainless steel hot stamping forming technology is analyzed. By comparison, the reasonable technological conditions of stamping forming is determined, so as to achieve the goal of optimizing forming parameters, and provide reasonable basis for cold, hot stamping experiments and the stamping process of high strength steel.Combined with the numerical simulation result, cold and hot stamping experiments of 304 stainless steel are conducted respectively. In working process, the servo press can delay in a short period. Precisely making use of this characteristic, the blank is heated, which is conducive to improving plasticity of materials. And strength of extension, resistance to deformation and rebound are declined, which is advantageous to material forming, guarantee the quality of part, and improving the die life. At the same time, in comparison with cold stamping, the result showed that hot stamping had fewer defects and the forming limit of hot stamping is higher. Also, numerical simulation result had higher credibility compared with experimental result. |
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