Numerical Simulation Analysis And Joint Strength Prediction Of Steel And Aluminum Mixed Self-piercing Riveting Forming Process

With the continuous development of the automotive industry,new lightweight materials and connectivity technologies need further studied in order to further improve the range and fuel economy.Steel and aluminum hybrid body provides new technical options for automotive lightweight,which is an important trend in the development of automotive body.Compared with the traditional steel body,the steel and aluminum hybrid body can significantly reduce the body weight when ensuring enough strength and stiffness.Self-piercing riveting,as one of the important connection processes of steel and aluminum body,the related research is not mature.It is important to study the high-precision simulation technique and strength prediction method.At present,the main methods of studying steel and aluminum mixing self-piercing riveting forming process and joint quality are numerical simulation and experimental exploration,and the theoretical research of joint strength prediction is relatively few.Through numerical simulation and experimental exploration methods,we analyze the influence of relevant process parameters on the riveting forming process and joint mechanical properties,propose a new ideal rivet length calculation method,and develop a new formula for cross tensile joint strength prediction.The main research contents of this paper are as follows:(1)A two-dimensional axisymmetric model of self-piercing riveting process of steel and aluminum dissimilar materials is established.Through the comparison of test and simulation results,the accuracy of the established two-dimensional axisymmetric finite element model is verified,which lays a foundation for the next study of steel aluminum hybrid Self-piercing riveting process and strength prediction.(2)Based on the joint section parameter data obtained by simulation,the optimal rivet length of 6063-T6 and B280 VK steel aluminum hybrid self-piercing riveting joints with different thickness combinations is studied by using the control variable method.It is found that there is a functional relationship between the optimal rivet length and the thickness of upper and lower plates.The existing two rivet length design formulas are compared and analyzed,and a new calculation formula of ideal rivet length is proposed.It provides theoretical guidance for rivet selection and enriching rivet production sequence in Self-piercing riveting.(3)Based on the high-precision numerical simulation model,through the control variable method,this paper focuses on the influence laws of six different process parameters such as plate thickness combination,rivet length,upper plate material strength,lower plate material strength,die depth and die diameter on the joint cross-section parameters,and analyzes the riveting forming process and joint mechanical properties under different process parameters,which provides theoretical guidance for the subsequent design process optimization.(4)According to the numerical simulation and experimental results,the practicability and limitation of the existing formula are analyzed,and a new formula for the strength is within 5%.Meanwhile,according to the new strength prediction formula,the joint failure mode prediction method and joint design criteria are proposed.