Occurrence and numerical prediction of surface defects during flanging of metallic sheets

Surface defects can develop on automotive exterior panels after drawing and flanging steps, during springback and may alter significantly the vehicle quality. These defects are characterized by a small depth below 0.5 mm and are then difficult to detect numerically. This study focuses on the surface defects for two parts: an industrial upper corner of a front door and a L-shaped part designed on purpose to reproduce at a small scale surface defects that occur after flanging. Dimensions of these defects are measured from profiles obtained either with a non-contacting method or a tridimensional measuring machine. Numerical simulations of the processes are performed with the commercial codes PamStamp2G or Abaqus and deformed meshes are analyzed in the same way as the experimental data. There is a good correlation between experiments and simulations concerning the spatial position of the defect and their dimensions. Moreover, a buckling analysis during springback is performed for the L-shaped part, showing that the position of the defect corresponds to one of the buckling mode.