Study On Air Bending And Springback Control Of High Strength Steel Sheet Under Warm Condition

With the increasing demand for lightweight vehicles and equipment,high strength steels such as DP980 are more and more widely used in the automotive industry due to their high strength and stable performance.In this paper,in order to solve the problems of DP980 in cold forming which is easy to break and has poor rebound consistency,based on the induction heating method,the warm bending performance of high strength steel sheets is studied,and the warm bending process and corresponding control methods are developed.This paper designs two induction heating coils,establishes a bending experiment system and experiment platform,explores a constant temperature heating method based on magnetic induction and power on-off technology,and determines the heating procedures for DP980 whose temperature range is from 100? to 600?.Based on the coupled hardening model,this paper proposes a new temperature softening term to enrich the hardening behavior and expand the degrees of freedom in the original model.The shear-corrected GTN meso damage theoretical model is derived,and the corresponding numerical calculation method is given.It is further developed on the basis of the ABAQUS VUMAT interface.Using the confidence domain optimization algorithm,the critical void volume fraction and other damage parameters of DP980 at different temperatures and different strain rates were obtained.The parameters such as the stress triaxiality,Lode angle and void volume fraction of the material during bending fracture were analyzed with punch loading process.In this paper,based on the induction heating experimental system,through detailed analysis of the relationship between the load displacement data of the V-bending analytical model and the basic mechanical properties of the material,the CWA(double secant)method was used to extract the alternative mechanical parameters of the material when it was bent at different temperatures and strain rates.And using the finite element simulation and CWA method,the BP(back propagation)neural network training data was obtained.Through training,the BP neural network algorithm is used to predict the bending angle after rebound.Combined with the BP neural network prediction library and the feedback control algorithm based on image recognition,the online control of the DP980's warm bending and spring-back process is realized.The online system is used to comprehensively control the problems of fracture and spring-back in bending and improve the forming accuracy of warm bending parts.