Effects Of Material Models On Springback Predictions And Compensations In Stamping Advanced High-Strength Steels (AHSS)

The sheet metal stamping process, as a kind of plastic processing method, is widely applied in automobile industry. Represented by DP steel, the advanced high-strength steel (AHSS), which has high strength and elongation and can satisfy the demand of carbody lightening and crashworthiness, has been widely used for automobile parts manufacture. However, the higher yielding limit of AHSS increases the springback after unloading, and its material property during reverse loading will induce Bauschinger effect, which makes the accurate prediction of springback more difficult.Problems arise in the subsequent assembly after springback and the requirement of the dimension precision can't be guaranteed, so it is important to obtain the precise springback and control the springback. The conventional isotropic hardening models, which don't consider Bauschinger effect appearing under reverse deformation, can't describe the deformation behavior of large-strain cyclic plasticity and the stress-strain responses at small-scale re-yielding after prestrain. Aiming at the above problems, with the financial support of national major project(2010ZX04014-072)and state natural sciences fund (51075269), this work is devoted to investigate the application of new material hardening models in springback prediction of AHSS and realizes the auto compensation of springback. The main research content is as follows,The two important factors that influence the prediction of springback are discussed- the material hardening model and the contact method.Yoshida-Uemori hardening model, defining a non-isotropic-hardening surface in the stress space, which considers kinematic hardening, can describe the early re-yielding, the smooth elastic-plastic transition with a rapid change of workhardening rate, and the work hardening stagnation appearing under reverse deformation as well as the strain-range and dependencies of cyclic hardening characteristics.The conventional contact method and smooth contact method are discussed. The conventional contact method can easily induce penetration problems and normal calculation error of the contact force, which cause error for springback prediction in numerical simulation. Smooth contact method can avoid these problems effectively and improve the prediction precision of springback.The conventional die-face adjustment, such as trial and error method, is high cost and low efficient. Based on the precise prediction of springback for stamping parts, in this paper, the LS-DYNA software is used to achieve auto springback compensation to modify the die shape by iterative algorithm, which makes the parts after forming can satisfy the shape requirement after springback. This method is of significance to guide the industry practical production.