An Investigation On The Restraining Force Of Double Drawbeads And The Subsequent Forming Performance

As an important part of the stamping dies,drawbead is used to provide restraining force,which can control the metal flow,obtain more uniform deformation and improve the quality of deep drawing parts.At present,to improve the computing efficiency.The equivalent drawbead model is adopted as the finite element models of stamping tools in most finite element simulation software.However,the equivalent drawbead model cannot calculate the deformation of sheet through the drawbead accurately,especially through the double drawbeads.The presently applied calculation methods do not take into account the sheet thinning and Bauschinger effect accurately,so their calculating accuracy results are not accurate enough.In addition,the deformation of the sheet through the drawbead should have an effect to the subsequent forming performance,but,up to now,there is not sufficient research on it.In this paper,the relationship of the double drawbeads restraining force(DBRF)with its influence factors was studied though experiment and theoretical methods,and the subsequent forming performance of sheet after the deformation through the drawbead was investigate by experiments.Detailed research contents are as follows.1.Take the half round drawbead and the rectangle drawbead as research objects,the drawbead restraining force was measured by experiments.The influences of drawbead radius R,drawbead height h,and the space between two drawbeads on the drawbead restraining force was studied according to the results of the experiments.And the relationship between the double drawbeads force and its influence factors was obtained through curve fitting by MATLAB.2.Based on the principle of virtual work and plane deformation assumption,a new model is proposed to improve the calculating accuracy of double drawbeads restraining force(DBRF)in sheet forming analyses.In order to take account of sheet thinning and Bauschinger effect caused by continuous bending process,a model to predict sheet thinning in the drawbead and the combined hardening model are introduced into the bending force model by Stoughton.The double drawbeads restraining force models were verified with the experimental results using CR4.The results show that the new model agrees better with the experiment data.3.Take the half round drawbead as research objects,the subsequent forming performance of sheet after the deformation through the drawbead was studied by experiments.The results show that after the deformation,the total elongation till fracture is less than that of the original sheet and the yield strength is increased.When the pre-strain is small,the subsequent fracture strength is less than the original fracture strength,and when the prestrain is large enough,the subsequent fracture strength is higher than the original fracture strength.