Trimming line development method of auto panel part with undercutting flange

Abstract

In most of auto-panel manufacturing, trimming is generally performed before flanging. Therefore, the acquisition of the optimal trimming line is one of the keys to obtain an accurate shape of a product. It is not easy to obtain a reasonable trimming line for auto panel part with undercutting flange. Analytical models can only deal with some simple stretch and shrink flanging parts. Section-based method unfolds flange along part outer boundary by defining many section planes. This method may produce inaccurate results for large deformation regions. The incremental simulation based method can generate more accurate trimming line by iterative strategy. However, it is still not widely accepted in the auto-industry since limitation of time and lack of information in the initial die design stage. In this study, a novel fast method to find feasible trimming line is proposed. One-step inverse finite element method (FEM) is used to analyze the flanging process because the strain paths are simple in flanging. The most difficult task of one-step inverse FEM is the generation of initial guess mesh. Robust generation method of initial guess mesh is presented specially to handle the undercutting flange regions. The new geometry method develops the final 3D part mesh with undercutting flange in triangle mesh parameterization way onto the drawing tool surface. The 3D mesh smoothing method with sliding constraint surface technique is utilized to smooth mesh distortion or overstretching after development. Finally, the 3D trimming line is extracted from the outer boundary after one-step inverse FEM simulation. The present trimming line calculation method is successfully applied to the complex industrial applications such as decklid and front fender. This method shows many benefits since trimming line can be obtained in the early die design stage.