Recently,a sheet metal forming simulation has become an indispensable tool for developing a new model of an automobile part within a limited short period.In these days,the utilization of a springback calculation of the formed part has been increasing.However,only a few papers on the prediction of surface defects have been reported in spite of serious needs.In this paper,surface defects in the door outer panel,especially those around the door handle embossment,have been investigated.Applying an explicit solver to the forming simulation,and an implicit solver to the springback calculation,we have tried to evaluate surface defects in the panel.In order to improve the accuracy of the simulation,numerical tools have been modeled including the precise shape of the draw beads so that the draw bead effects on both the material flow and the restraint on the springback deformation have been considered.Compared with the actual panel shape,which shows apparent surface defects,the simulated result has closely predicted the above defects around the embossment.To demonstrate the applicability of our simulation,a few sensitivity analyses have been carried out,modifying forming conditions such as blank holder force.Each result has shown slight but distinctive differences in the cross section profile of the panel.As a result,it has been realized that the influence of each considered factor on surface defects is qualitatively consistent with our practical knowledge.
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