Research On Springback And Twist Of Ultra High Strength Steel Thin-walled Components With Asymmetric Section In Roll Forming Process

In recent years,energy,environmental protection and safety issues have gradually become prominent.Automotive lightweight has become the inevitable trend.Ultra high strength steel(UHSS)is the important measure to achieve lightweight and the application of UHSS thin-walled components with asymmetric section is becoming increasingly widespread.In order to solve the problems of large springback,obvious twist and difficult to control in roll forming process of UHSS thin-walled components with asymmetric section,basic tests,theoretical analysis,finite element modeling,numerical simulation and industrial experiments were conducted.Constitutive model and finite element model of complete roll forming process were built;the mechanism,forming law and control method of springback and twist of UHSS thin-walled components with asymmetric section in roll forming process were studied.The findings provide the guidance for high-quality production of UHSS thin-walled components with asymmetric section in roll forming process.The main contents and work results are as follows:(1)Based on basic tests and theoretical analysis models,the model including the Young’s modulus variation,anisotropic yield criterion and kinematic hardening model were presented.The finite element model of multi-pass complete roll forming process of UHSS thin-walled structures with asymmetric section was established.The mechanism of springback and twist of UHSS thin-walled components with asymmetric section in the roll forming process is revealed.Cyclic loading-unloading-reloading tests were conducted.It was found that the Young’s modulus of UHSS MS1500 decreses rapidly firstly with the increase of plastic strain and tends to a constant value.The Young’s modulus variation models were established with different calculation methods.The anisotropy and Bauschinger effect of MS 1500 were analyzed and the influence of anisotropic yield criterion and hardening model on the prediction accuracy of springback and twist of UHSS thin-walled components with asymmetric section was analyzed.The combination of the chord elastic modulus model and Y1d2000-2d yield criterion with the Chaboche model can effectively improve the prediction accuracy of springback and twist of UHSS thin-walled components with asymmetric section.Based on the finite element model of the complete roll forming process of UHSS thin-walled components with asymmetric section,the mechanism of springback and twist of UHSS thin-walled components with asymmetric section was analyzed and revealed.The findings provide theoretical basis and guidance for the subsequent research on the forming law and control methods.(2)Based on the characteristics of UHSS thin-walled components with asymmetric section in roll forming process,the forming law of springback and twist was studied.Based on numerical simulation methods,the influence of geometric parameters on the springback and twist of UHSS thin-walled components with asymmetric section was analyzed.Springback decreases with the increase of strip thickness and web width,and increases with the increase of vertical edge height and forming angle.Twist is mainly related to the asymmetry of the section and can be determined with the inclination angle of the inertia principal axis of the section.The effect of different forming strategies on springback and twist of UHSS thin-walled components with asymmetric section was conducted.It was found that UDT(USTB Durable T)loading method,fixedarc-length method,and downhill method can effectively improve springback and twist.The orthogonal test was designed and carried out to study the effect of key process parameters on springback and twist.It was found that the number of forming passes and roll gap had the greatest impact on springback;springback decreases with the increase of forming passes and roll diameter,and increases with the increase of roll gap.The number of forming passes and roll diameter have the greatest impact on twist;twist decreases with the increase of forming passes and the distance between two roll stations,and increases with the increase of roll diameter.The findings provide theoretical basis and guidance for the control method of springback and twist of UHSS thin-walled components with asymmetric section.(3)Based on production practice,the combined control method for springback and twist of UHSS thin-walled components with asymmetric section was studied and verified through industrial experiments.UDC(USTB-Durable Combination Control for Springback and Twist)combined control method was proposed,which is combination and iterative strategy of process compensation method and angle deflection method to comprehensively control springback and twist of UHSS thin-walled components with asymmetric section.Compensation parameters of UDC combined control method was determined,and the effectiveness of UDC combined control method was verified with numerical simulations.Based on the actual production conditions,industrial experiments and applications were conducted on the asymmetric open section and asymmetric closed section of UHSS to verify the effectiveness of UDC combination control method,achieving precise forming of UHSS thin-walled components with asymmetric section.The findings provide the theoretical and practical basis for the comprehensive control of springback and twist of UHSS thin-walled components with asymmetric section in roll forming process.