Characters And Control Methods Of Torsion Springback In HSS Stamping

Usually there is a problem that the torsion springback of panel is difficult to be controlled in the stamping process, especially using HSS (High Strength Steel). Based on the consideration of lightweight and safety, the application of HSS in automotive panel is more and more popular. It will make a bad accuracy in the car assembly if the springback can't be controlled well. Torsion springback of automobile part is one of the main forms of springback, which is complex and hard to control and brings difficulties of manufacture precision. So, torsion springback problem is always a hotspot in automotive industry group and academia.The research was based on practical application of engineering, Firstly, various forms of torsion springback were classified and summarized. Secondly, basic features of torsion springback were analyzed. Finally, basic reasons and effect factors of torsion springback were studied. Based on the engineering practice, this paper contains torsion springback analysis, evaluation methods and control methods. Main works of this paper are presented as follows:1.According to the widespread investigation on torsion springback, the auto parts which were more likely to bring torsion springback were classified, summaries of main basic characteristic of torsion springback were obtained. The general forms of torsion springback of the HSS by actual parts were explained, such as A pillar reinforcement, door threshold etc. A method named"torsion stiffness"was proposed to analysis the reasons for torsion springback and influencing factors, commonly used methods and techniques of production were proposed to reduce torsion springback by the aspects including remaining torque and the torsion stiffness.2.An analytical method to calculate the springback of characteristics section was suggested, sidewall curl was also considered and taken account into springback computation, this strategy improves the accuracy of the proposed method. The method was validated by the U stamping, and it indicated that the method has a higher accuracy. Furthermore, a method to predict tendency of torsion springback was proposed, the process of torsion springback can be divided into "primitive springback" and "mutual influence". Firstly, the primitive springback of section was calculated by analytical method, and then, shape features were taken into account to analysis mutual influence of different sections. Meanwhile, by this method, we could analysis the causes of torsion springback. Cases study for basic feature with turning shapes and various section shapes were carried out. The torsion springback of the given parts were analyzed by finite element method, and then some measures to promote accuracy and predict tendency of torsion springback were put forward.3.Some basic features such as parts with turning shapes, parts with various section shapes, non-uniform material flow in stamping process were proposed. Based on experiments and simulation of FEM, cases to the effect of torsion springback were studied, such as the basic feature size, properties of stamping materials, stamping techniques etc.4.A novel method to evaluate parts' torsion springback by springback movement of characteristic cross-section method was proposed. This method could obtain the parameters of springback movement in the characteristic cross-sections, this paper attempts to represent parts' torsion springback by parameters. A program was developed to determine the deformation of characteristic section, the deformable movement included displacement and rotation, and this program divided characteristic sections with several areas by convergence estimation. The paper studied on a part's springback with arched surface by experiment and simulation analysis, the result verified validity of this model.5.A system which can control springback is presented based on the springback movement of characteristic cross-section method. Firstly, the result of springback could be calculated by FE system or obtained by scan way. Secondly, the parameters of springback movement in the characteristic cross-sections could be analyzed by springback movement of characteristic cross-section method (SMCS). Thirdly, springback control section could be obtained based on the parameters of springback movement by compensation factor method. Finally, based on the origin CAD surface and the control section of springback, the mould was compensated for springback by application of shape global deformation method. The practice engineering cases proved that the system can save more time to deal with springback of parts with arched surface, the result of springback compensation is right and applied and the method is worth to spread.