Numerical Simulation Research Of High-Strength Steel Hydrodynamic Thermoforming

Nowadays, the automotive industry has developed rapidly, especially the green enviromental protection cars become more and more popular, energy-saving, enviromental protection and lightweight vehicles have become the main develpoment direction of the automobile industry. Sheet hydrodynamic thermoforming technology is under the condition of meet the lightweight and produce a kind of advanced forming technology, which combines the advantages of hydrodynamic forming technology and thermoforming technology, it can effectively improve the quality of forming parts. As the growing demand for the high-strength steel in the automotive body, to researching high-strength steel hydrodynamic thermoforming would be significance.In this paper, the hydrodynamic thermoforming of the flat bottom cylindrical cup and the ball bottom cylindrical cup were respectively studied based on the finite element simulation software Dynaform. Compared with the deep drawing performance of the flat bottom cylindrical cup which is processed by the normal hydrodynamic forming and the hydrodynamic thermoforming. Analyzed the influence of pre-bulging pressure, fluid chamber pressure, sheet forming temperature, blank-holder gap on forming quality of cylindrical cup. Appropriate pre-bulging pressure made the cylindrical cup form the soft drawbead during the early forming so as to improving the quality of forming parts. It can increase the beneficial friction between the sheet and the punch, thereby reducing the wrinkling and rupture of the ball bottom end cylindrical cup and vacant area if the fluid chamber pressure was choosen appropriately. Low temperature of sheet forming is easy to make the ball bottom cylindrical cup material accumulation appears in vacant area, the high temperature can make the material soften, on the premise of guarantee the quality of parts should select reasonable forming temperature. Blank-holder gap can control the cylindrical cup flange portion of the metal flow, and it can get uniform wall thickness of forming parts if choosing the reasonable blank-holder gap.Combined the Dynaform software with the response surface analysis method, and optimized the hydrodynamic thermoforming parameters of the ball bottom cylindrical cup in this paper. The fluid chamber pressure, sheet forming temperature, blank-holder gap were selected as the design variables, the design goal is the minimum wall thickness after forming the ball bottom cylindrical cup, based on BoxBehnken Design response surface, and set up with the minimum wall thickness as the objective function of the response surface modle. The optimal parameters of the model were determined through the regression equation of variance analysis and F test. The model predicted optimal parameters of the finite element numerical simulation, and compared the minimum wall thickness with the model prediction, the error rate is less than 1 %, which verifying the response surface model of reliability.