Study On Springback Prediction Of High Strength Strip Steel In Rollforming

The roll forming process is a complicated deformation process. Recently, the advanced high strength steel is more and more extensively applied. However, because of the high hardening rate, it is difficult to be formed compared to the low carbon steel plate commonly used in the forming process, and especially, the control of forming spring-back has become one of the dilemmas in the roll forming process of advanced high strength steel. The method of finite element emulation is more and more applied in the roll forming. Using such method to treat the emulation in the forming process, the better results can be achieved, but the treatment for the forming spring-back is not ideal. Such problems can be attributed to many reasons, such as the material model is not perfect, and the Bauschinger Effect of the materials is neglected. Therefore, for the roll forming emulation of advanced high strength steel, developing one kind of material model which can resolve the Bauschinger Effect is a significant job. Applying the material model more coincident with the practice can make the emulation of roll forming process closer to the practice. This is the basis of emulation of forming spring-back. It will provide the foundation for the forming spring-back control. The spring-back can have the great influence on the size and shape precision of the forming products and especially on some materials with apparent processing hardening, such as the advanced high strength steel, have greater influence.In this paper, setting up a roll forming model with Abaqus FEM code to simulate and analysis the roll forming process of U section of Advanced High Strengthen Steel. The author carried out the primary finite element simulation analysis on the springback occurring while using AHSS in roll forming, and got the basic rule by which the model parameters affect the springback.The problem of springback occurs while forming many metals, including Advanced High-Strength Steels (AHSS). The springback is a process in which the internal stress is released, and it has great influence on the precision of metal forming. Especially for the materials apparently hardened after being processed, such as High-Strength Steels, the springback become the problem difficult to be resolved in the simulation of metal forming. Numerical simulation method and elastic-plastic constitutive relation with hybrid hardening are adopted, the stress compensation updating algorithm based on elastic tensor is brought forward, isotropic hardening coefficient is introduced, the steps for computation of the elastic-plastic constitutive relation in FEM are given, and the subroutine VUMAT is developed in the plat of ABAQUS/EXPLICIT, whose reliability is verified by a single element model. In this paper, the author carried out the primary finite element simulation analysis on the springback occurring while using AHSS in roll forming, and got the basic rule by which the model parameters affect the springback. Theoretic analysis on the regularity above is giver further. The conclusion can do instruction to the process of roll-forming in factory.Setting up a roll forming model with U section, materials DP800 have been applied to the model in order to study on its spring-back angles. The spring-back angles of DP800 has a marked difference characters; the deformation energy of DP800 is increased obviously. Spring-back of simulation is contrasted with calculation of BISWAS method. The results indicate that, BISWAS equation can not be directly used to calculate the spring-back of roll forming of AHSS. The changed yield stress S should be considered, a new calculation method should be developed.