Trimming line design using new development method and one step FEM

In most of automobile panel manufacturing, trimming is generally performed prior to flanging. To find feasible trimming line is crucial in obtaining accurate edge profile after flanging. Section-based method develops blank along section planes and find trimming line by generating loop of end points. This method suffers from inaccurate results for regions with out-of-section motion. On the other hand, simulation-based method can produce more accurate trimming line by iterative strategy. However, due to limitation of time and lack of information in initial die design, it is still not widely accepted in the industry. In this study, new fast method to find feasible trimming line is proposed. One step FEM is used to analyze the flanging process because we can define the desired final shape after flanging and most of strain paths are simple in flanging. When we use one step FEM, the main obstacle is the generation of initial guess. Robust initial guess generation method is developed to handle bad-shaped mesh, very different mesh size and undercut part. The new method develops 3D triangular mesh in propagational way from final mesh onto the drawing tool surface. Also in order to remedy mesh distortion during development, energy minimization technique is utilized. Trimming line is extracted from the outer boundary after one step FEM simulation. This method shows many benefits since trimming line can be obtained in the early design stage. The developed method is successfully applied to the complex industrial applications such as flanging of fender and door outer.