| Blank-holder force is an important technological parameter in sheet metal forming process,the main function of blank-hold force is used to control the flow of material and to prevent the occurrence of wrinkling of sheet metal.The traditional constant blank-holder force is often difficult to achieve the ideal forming effect in the face of body panels and other complex shape parts.Therefore,changing with pressure coil position and punch stroke of variable blank-holder force technology has been paid more and more attention by researchers both at home and abroad.Although the technology of variable blank-holder force can significantly improve the forming performance of the stamping parts,it is difficult to popularize in engineering practice at present.Meanwhile,majority of the stamping parts often appear parts defect in the stamping process,partition variable blank-holder force is needed in local control.In view of the difficulties in the application of variable blank holder force technology in engineering application,this paper presents a method for fitting the variable blank holder force with gradient drawbead,which can achieve the effect of variable blank holder force under the condition of constant blank holder force.The main work is as follows:1.The simulation of the inner door panel is carried out to determine the area where the control of the blank holder force is needed,and then,VBHF curve which is obtained by using optimization calculation.2.According to the amount of contraction interval of the sheet edge node,the number of sections of the drawbead is determined.The shrinkage range of VBHF curve derives from relationship between the constrained force of VBHF on the blank and the travel distance of the blank edge and the constrained curve of gradient drawbead,by which the parameters such as the number,location and the geometric dimension of gradient drawbead can be obtained.3.The variation in thickness of formed parts is seen as optimized objective function.Using the equivalent drawbead to simulate the inner panel of the door,determine the fitting accuracy,verify the feasibility and validity of gradient drawbead fitting VBHF technology.The fitting Descending VBHF by Gradient Drawbead has a certain guiding significance to improve the quality of sheet metal forming and to promote the technology of changing the blank holder. |
