Abstract:

The forming process of the front-end three-dimensional skin of China Electric Multiple Units (CEMU) was simulated and analyzed using the general finite element software Autoform. The influences of the process parameters such as blankholder force, drawbead, die radius, draw depth, friction coefficient and die gap on the forming of the V-section skin with large thickness, shallow drawing depth and twisted structure were investigated. The reasons for the forming defects such as insufficient stretching and poor contour accuracy were analyzed and the controlling methods were proposed. The results show that insufficient stretching is mainly originated from the lack of flow resistance, which can be controlled by setting proper drawbead and increasing the blankholder force; for the investigated long strip skin in this work, variable intensity drawbead is recommended. Poor contour accuracy is mainly caused by large springback. Process parameter optimization can improve the contour accuracy to some extent, and degrees of the influence parameters are in the order: die radius > friction coefficient > die gap > draw depth. Compensation to the surface based on springback can significantly control the contour accuracy. For the 4 mm 5083-H111 aluminum alloy, the optimal compensation is 1.2 times of the springback amount. Forming tests were conducted according to the simulation results, and high quality compensations were achieved, which prove the validity of the proposed defect controlling methods.

Key words: materials synthesis and processing technology, China electric multiple units, three-dimensional skin, numerical simulation, process parameters, defect control