Research Of Variable Blank Holder Force Optimization Design Based On Approximate Model

Blank holder force is an important process parameter in sheet metal formingprocess, the main function of blank holder force is to generate frictional resistance inorder to increase the tensile stress of sheet metal, to control the flow of material and toavoid the wrinkling of sheet metal. In sheet metal forming process, the traditionalconstant blank holder force is often difficult to control the defects such as wrinkling,springback and crackling simultaneously. So some researchers put forward variableblank holder force control method, which set different blank force in differentlocations and travels, and can improve sheet metal forming quality by fully takingadvantage of the formability of material.Generally, according to the load mode, the control force of blank holder force i sdivided into five categories, constant load mode, increase mode, decrease mode,mixed mode and pulsation mode. At present, the research of variable blank holderforce technology by domestic and foreign researchers mainly focus on simple shapeparts such as conical and cylindrical parts, but as to the question that which kind ofload mode is most conductive to the forming process of sheet metal, researchers fromdifferent countries have different opinions based on their own research outcomes, auniform mode has not been given. Due to the shape of different stamping parts arealways different, the choice of variable blank holder force should be determinedaccording to the shape of actual part. Some existed research has applied optimizationmethod to get the curve of variable bank holder force, but it has always been adifficulty on how to describe the curve during the optimization process. In view of this,this paper proposed a manner that curve is constructed by points to obtain theexpression of variable bank holder force curve, the main research content is:（1） The variable blank holder force forming process of stamping is analyzed,and a new method to determine the upper and lower limits of variable blank holderforce is put forward.（2） The punch stroke is divided into some small segments, some variableblank holder force sampling points is set up on every segment by using UniformLatin-square experiment design method, the smooth variable blank holder force curveis constructed through these sampling points.（3） Taking the thickness variation of formed part as objective function, the variable blank holder force curve is optimized by the integration of Respond SurfaceModeling technology, Uniform Latin-square experiment design method and GeneticAlgorithm, the feasibility of the method to acquire variable blank holder force isvalidated through simulation.In allusion to the stamping process of top beam connection plate, a design is putforward based on Respond Surface Modeling technology and Uniform Latin-squareexperiment. Taking the maximum grid thickness difference of formed part as objectivefunction, the variable blank holder force load curve is optimized through GeneticAlgorithm. Example analysis results show that the stamping quality of sheet metal canbe improved by using the optimized variable blank holder force load curve.