多点成形中压痕的数值模拟及极限成形力的分析

Numerical simulation of dimples and analysis of limit forming forces in multi-point forming of sheet metal

压痕是多点成形中特有的成形缺陷之一,对压痕形成过程进行模拟时,采用实体单元比壳单元计算更准确.但是板料较薄时,采用实体单元划分的有限元很多,计算时间极长.为获得最佳的计算效率及模拟结果,对不同材料和不同厚度的球面和马鞍面样件进行了对比的数值模拟.结果表明,当板厚与板宽的比值小于0 015时,采用壳单元模拟压痕也能得到比较准确的结果,而当比值大于0 015时,则应采用实体单元.在此基础上,对不同板厚、不同曲率半径下的马鞍面和球面件出现压痕时的极限成形力进行分析,得到了厚向压应变为1%和5%的压痕对应的成形力极限图.

Dimple is a particular defects in multi-point forming(MPF) of sheet metal, solid element is more accurate than shell element when the process of dimple formation is simulated. However, if solid element is employed when blank is relatively thin, the number of elements will be extraordinarily large and a very long of CPU time will be cost. To obtain reasonable computational efficiency and simulation results, sphere and saddle surfaces part with different thickness and materials are simulated and compared. Results indicate that the simulation results of dimple by shell element model are also accurate when the ratio of thickness and wideness of blank is less than 0.015. But when the ratio is more than 0.015, solid element model should be adopted. Based on above results, the limit forming force of sphere and saddle parts to obtain accurate results with different thickness and different curvatures are analyzed when dimples occur, and the limit forming force diagrams are plotted while thickness strain of dimples are 1% and 5%.