Abstract: The accurate prediction of the multi-stage sheet metal forming including springback is of great signifi- cance for stamping industries,and the Bauschinger effect is a key factor influencing the accuracy.In this paper,an improved multi-stage combined hardening model is constructed.In the model,based on the two-yield-surface model of the Yoshida-Uemori hardening model,the equivalent back stress of the boundary surface between stages is calcu- lated for each stage by using the nonlinear isotropic hardening equations with different factors influencing strain paths.In a real tension and compression test of DP600,in comparison with other hardening models,both the Yo- shida-Uemori model and the constructed model can better reflect the Bauschinger effect and calculate the stress- strain curve more accurately.In a multi-axial tension and compression test,the constructed model is more accurate than the Yoshida-Uemori model.By the experiment and numerical simulation of the multi-stage manufacturing process of an A-pillar,it is proved that，in comparison with other constitutive models,the constructed model can achieve a higher accuracy in predicting springback in the numerical simulation of the multi-stage sheet metal for- ming.

Key words: multi-stage, sheet metal forming, combined hardening, Bauschinger effect