Study On The Equivalent Drawbead Force Model

In the forming process of automobile body panels,drawbead structure is used to provide resistance force,which can control the metal flow,obtain more uniform deformation and improve the panel quality.At present,to simulate the drawbead structure,the equivalent drawbead model is adopted in the mainstream commercial finite element simulation software.However,it was found that the deformation behavior of the sheet metal cannot be simulated accurately by using the equivalent drawbead model.In this dissertation,combinations of experiment,theoretical and numerical simulation methods were used to study the influence factors of the drawbead force and present a modified equivalent drawbead model,detailed research contents are as follows:The influences of drawbead fillet radius,drawbead height,drawing speed on the drawbead force were studied through the orthogonal experiment and single variable experiment.With the comparison between experiment drawbead force and equivalent drawbead force,it's found that there's a general bias of them,and the correction method based on the error was proposed.According to the results of the study,the preliminary design and adjustment principle of the drawbead was presented.According to the plastic mechanics theory,the stress and strain distribution law of the sheet metal flowing through the drawbead was deduced by using the plane strain hypothesis and the material anisotropy assumption.Based on the phenomenon of the separation between the sheet and the drawbead,the modification of effective bending radius was proposed.On the basis of this,the thinning formula in the equivalent drawbead model was modified,with the comparison to the experiment results,the validity of the modification was verified.Meanwhile,considering the modified thinning formula and strain variation formula,an modified equivalent drawbead model was established,and the validity of the modified model was verified by comparing with the experiment results.Finally,using original model and modified drawbead model,a standard test of Numisheet2005 was calculated,and the calculated values were compared with the experiment results,with this,the effects of different models on the sheet thinning,the punch load and the springback were studied.Also,by using the modified drawbead model,an improvement in a certain extent of prediction accuracy of the punch load and the springback was verified.