Rapid Springback Compensation for Age Forming Based on Quasi Newton Method

Iterative methods based on finite element simulation are effective approaches to design mold shape to compensate springback in sheet metal forming.However,convergence rate of iterative methods is difficult to improve greatly.To increase the springback compensate speed of designing age forming mold,process of calculating springback for a certain mold with finite element method is analyzed.Springback compensation is abstracted as finding a solution for a set of nonlinear functions and a springback compensation algorithm is presented on the basis of quasi Newton method.The accuracy of algorithm is verified by developing an ABAQUS secondary development program with MATLAB.Three rectangular integrated panels of dimensions 710 mm′750 mm integrated panels with intersected ribs of 10 mm are selected to perform case studies.The algorithm is used to compute mold contours for the panels with cylinder,sphere and saddle contours respectively and it takes 57%,22%and 33%iterations as compared to that of displacement adjustment(DA)method.At the end of iterations,maximum deviations on the three panels are 0.618 4 mm,0.624 1 mm and 0.342 0 mm that are smaller than the deviations determined by DA method(0.740 8 mm,0.740 8 mm and 0.713 7 mm respectively).In following experimental verification,mold contour for another integrated panel with 400 mm×380 mm size is designed by the algorithm.Then the panel is age formed in an autoclave and measured by a three dimensional digital measurement devise.Deviation between measuring results and the panel’s design contour is less than 1 mm.Finally,the iterations with different mesh sizes(40 mm,35mm,30 mm,25 mm,20 mm)in finite element models are compared and found no considerable difference.Another possible compensation method,Broyden-Fletcher-Shanmo method,is also presented based on the solving nonlinear functions idea.The Broyden-Fletcher-Shanmo method is employed to compute mold contour for the second panel.It only takes 50%iterations compared to that of DA.The proposed method can serve a faster mold contour compensation method for sheet metal forming.