Research And Numerical Simulation On Variable Gap Forming Technology Based On Principle Of Discrete Blank-holders

Blank-holder is one of the key technologies to suppress defects such as tearingand wrinkling in deep drawing process, and can improve the quality of stamped partseffectively. Variable gap blank-holder process is a new technology combined flexibleforming ideas with existing traditional blank-holder process. Using discreteblank-holder to replace the traditional rigid blank holder, the novel blank holder canbe assenmblied according to the target shape. Thus it is posiibit to reduce the costs,short the device trial cycle, improve the utilization of materials and productionefficiency.The main research contents and conclusions:(1) Mechanis anslysis of the rectangular box in deep drawing process throughdividing the rectangular box into different forming region according to the geometricanalysis. Besides analysis of the state of stress and strain in the flange deformationprocess has been carried out, as the basis of the adjustment of blank holder gap.(2) On the basis of the sheet metal forming theory，the variable gap blank holdertheory of FEA and digital modeling has been approatched. A digital model has beencreated based on the FEA numerical simulation software，meanwhile some problemshas been dealed with such as element selection，boundary conditions，definition ofcontact and friction.(3) Studying the effects and impact on the formability of the rigid blank-holderand discrete blank-holder by applying different constant blank holder gap. Thenumerical simulation result indicates that there was few difference between them，andthey did not meet expectations. Through discussing the evaluation criteria of fractureand wrinkling，the criterion has been a different△T between maximum thickness andminimum thickness as in this dissertation.(4) Adjustment of the discrete blank-holder gap in order to improve the formingdepth. Orthogonal experiment was used to further optimization variable gapadjustment. Optimization process was mainly introduced and the optimum was validated by the numerical simulation with good forming result.The forming depthincreased by14.13%and the largest thickness increased by6.14%. It shows that thevariable gap blank-holder technology can improve the forming quality of panels.(5) Approaches on the change of friction coefficient in different regions of theblank in the contact area and analysis of its influence on the forming results. It turnedout that different regions have different effects on the forming results. More discreteblank-holders can the occurrence of wrinkling and make the stress distribution moremuch uniform. While the thickness of the sheet metal, yield strength and elasticmodulus are smaller, small blank-holder gap in the process of forming will be needed.However, if the gap was too smaller, it will cause cracking defects. It has beenrecommended that to choose reasonable the blank-holder gap. In addition，theincreased adjustment of blank-holder gap, can make a greater drawing depth andbetter forming effect in the sheet metal deep drawing.