Equivalent Drawbead Model Research Considering Bauschinger Effect

In the forming process of large automotive panels,as the increase of the complexity of the mold,sheet metal flows not evenly in different directions,which may lead to wrinkling,cracking or other process defects in some areas.Drawbead can effectively control the sheet flow restraining force,so that parts forming a higher quality.In the current mainstream finite element sheet forming softwares,usually use the equivalent drawbead model to calculate the drawbead restraining force instead of the true drawbead structure,but the equivalent drawbead model is not accurate enough.When throughing the drawbead structure,the sheet have to be bent and rebent,where the Bauschinger effect exists,but the current equivalent drawbead models have not considered Bauschinger effect.In this paper,a combined hardening model is established and used in equivalent drawbead model,and a modified equivalent drawbead model which considering Bauschinger effect is established.Nowadays,people have not did too much research on double drawbead,a double drawbead device is designed in this paper,and the double drawbead restraining forces in different drawbead heights and radii are obtained,and the design criterion of double drawbead is established.The main content of this paper is:Based on Voce isotropic hardening model and Armstrong-Frederic nonlinear kinematic theories,a combined hardening model is proposed.For CR4 sheet steel,tension-compression tests are carried out in different prestrains and obtain the parameters in the combined hardening model,the experiment results verified the veracity of the combined hardening model.The combined hardening model is introduced into the equivalent drawbead model,in the formula for calculating the forming resistance at the corners of drawbead,Bauschinger effect is introduced into equivalent drawbead model.Using the drawbead test device,the drawbead restraining force of semicircular drawbead and rectangular drawbead at different drawbead heights and drawbead radii are obtained.Compared with the equivalent drawbead model,it proved the accuracy of the improved drawbead model.In this paper,a double drawbead test device is designed,the double drawbead restraining forces of semicircular drawbead and rectangular drawbead with different drawbead heights and radii are obtained,structural design criteria for drawbead is proposed,and the relationship between the double drawbead restraining force and single drawbead restraining force is analyzed.