Investigation For Hot-stamping Of U-shaped Beam With Variable Height Based On Numerical Simulation

The environment problems rised by the popularity of cars caused a lot of people’s attention, the safety of motor vehicle and auto light-weighting have became the general trend of the current auto industry development. Automotive lightweighted aims to safeguard the safety of the cars on condition of enough structure strength and stiffness, as far as possible to reduce fuel consumption by reducing the overall weight of the body. Current vehicle high strength steel is more and more widely used in the automobile industry, it has became a common way to ensure automotive lightweight and safety performance. Hot forming technology posses the characteristics of good plasticity, deformation resistance, high forming limit and forming precision, which could produce complicated advantages, such as the geometry of the workpiece, to provide the high quality for auto parts and components to meet the requirements of automotive lightweighting demands.The U-shaped with variable height is a typical part in hot stamping, in this article, 22 Mn B5 sheet with 2mm thickness is chosen as the research object, and the Pamstamp2 G software is employed to do finite element simulation analysis in the condition of the bigger altitude difference, the relationship of different altitude difference in variable height U-shaped and its die design in forming and the impact of its mechanical properties. The research content and conclusions are as follows:Having analyzed the variable height u-shaped beam of different height in hot stamping die design, the corresponding design criterion with different wing edge radius values was found out. Simulation results showed that when the height difference increased, the required wing edge radius values growed along. For the same height difference, larger wing edge radius could decrease the stress and strain of the part, and the part thickness distribution gradually became tend to be more uniform.Under the help of Pam-stamp2 G software in this paper, the influence of process parameters on the mechanical properties of parts such as stamping speed, friction coefficient, the initial mold temperature and the holding time were presented. And the detailed results are as followed:(1)Bainite transformation came to light before quenching when the stamping speed was less than 80mm/s, while the stamping speed was in the 80-120mm/s range, the sheet metal did not arised martensitic transformation before quenching. Considering the forming performance and manufacturing cost comprehensively, the best choice of stamping speed was chosen to remain in 80-120mm/s.(2)The martensite content of part was less than 80% when the die clearance was greater than 1.1t after quenching. Meanwhile the cooling rate of the side wall was less than 30℃ / s when the die clearance was 1.1t in the process of quenching. The part had good forming performance when die clearance was 1.0t and 1.05 t.(3)The temperature of part did not completely fall to the point of the martensitic transformation temperature when the holding time was less than 10 s, Accurate analysis for the temperature-drop showed that temperature felling below the end of the martensitic transformation temperature completely took 10.4s.(4)With the increased of the die temperature, the maximum and minimum temperatures of sheet component grew at the end of stamping, when the die temperature came up to 150℃, the hardness of part had dropped below 400 HV. In condition, the part had better mechanical properties when the die temperature was inferior to 50℃.At last, the adequate process parameters combination are as follows: the range of stamping speed is 80-120mm/s; the range of die clearance is 1.0-1.05t; the quenching time is more than 10.4s; the die temperature is below 50℃.