Abstract: Before flanging auto-body panels, a feasible trimming line should be obtained, otherwise the final part shape after flanging cannot meet the dimensional requirement. To reduce the cost and lead time of developing a trimming die, a method to obtain the trimming line in flange process is proposed on the basis of blank grid deformation. The blank is etched with square grid，and the processes before flanging are carried out. Based on the estimated trimming line, the part shape is obtained, and the coordinates of mesh points on the trimming region are measured, then the part is flanged. The coordinates of mesh points on the trimming region before and after flanging are measured. On the basis of the part meshes before and after flanging and the edge line of part after flanging, the position of trimming line before flanging is determined by the mesh proportional deformation before and after flanging. If the edge line of the stamped part still has dimensional problem, this method can be used repeatedly to optimize the trimming line. This method can be used in die debugging and in simulation work. An example of determining the trimming line of a car floor part is provided to verify this method.

Key words: Car body, Grid, Stamping, Trimming line