Abstract:

In order to control the springback in the forming process of sheet metal,a synthetical method to evaluate the springback is proposed based on multi-objective opitmization.In this method,two objective functions are established,one of which considers both the equivalent stress deviation and the coordinates of Gaussain integration point,and the other considers the equivalent plastic strain.Then,an integrated optimization model based on the springback control is put forward by combining the design of experiment,the response surface method and the multi-objective genetic algorithm with LS-DYNA keyword file.Moreover,the influences of variable blank holder force（VBHF） and drawbead restraining force on the springback are analyzed.The results show that（1） when the VBHF takes its value first small and then great,large plastic deformation can be achieved,and larger blank holder force in the later stage may lead to small equivalent stress deviation in the thickness direction,thus significantly inhibiting the springback;（2） a reasonable configuration of drawbeads adapting to the product shape and appropriate drawbead restraining forces also have some effects on the springback reduction;and（3） the amount of springback decreases from 1.95250mm to 0.67451mm after the optimization,which means that the proposed multi-objective functions are effective in evaluating the springback.

Key words: springback, multi-objective optimization, sheet metal forming, process parameter, variable blank holder force, drawbead restraining force