A framework for predicting subtle surface distortion in sheet metal flanging

The subtle distortions after flanging operations on outer automotive panels are highly undesirable on class-1 finish panels. Since existing finite element software do not have the ability to accurately predict or capture these subtle distortions, die designers rely on expensive and time-consuming physical tryouts to verify and adjust their design. Thus, this work aimed to gain an understanding of the distortion behavior and to develop a numerical tool that captures these subtle surface distortions. Both theoretical and experimental approaches were carried out. The energy-based buckling predictor was developed as a post-processor of numerical simulations to assess the distortion tendency. The experimental work consisted of pre-stretching, trimming and flanging. Surface scanning was conducted to verify the applicability of the buckling predictor. The comparison between the predictions and the experimental results showed that the predictor could predict surface distortions in the flanged panels.