Research On Clinching Joining Process And Joint Performance Of Automobile Body Heterogeneous Materials

With the increase in the number of cars,the lightweight of automobiles has become an inevitable trend in the development of automobiles.The use of a variety of materials is an important means to achieve lightweight car body.Due to the difference in physical properties and chemical properties such as melting point and density of heterogeneous materials,the conventional spot welding process cannot meet the connection between heterogeneous materials.As a new type of green joining process,the rivet-free riveting technology does not require holes and other accessories,and has no heat input,which can effectively avoid the problem of hard and brittle phases formed by thermal connections and different melting points of heterogeneous materials.This paper combines part of the research content of the key technology innovation project of key industries in Chongqing,“Research and Application of Key Technologies for Automotive Lightweight Design and Forming(cstc2015zdcy-ztzx0175)”,and uses the finite element method for the problem of connection and forming process of vehicle heterogeneous materials.The rivet-free riveting forming process and joint performance of heterogeneous materials such as 5754 aluminum alloy and high-strength steel for vehicle plates were numerically simulated,And the process parameters are optimized,and finally the forming process is tested and analyzed.The specific research contents are as follows:(1)Simulation of the forming process of the rivet-free riveted joint.A finite element simulation model of 1mm 5754 aluminum alloy and 1mm high-strength steel without rivet riveting was established in ABAQUS to simulate the forming process of heterogeneous materials without rivet riveting,and the stress and strain of the material during the forming process were analyzed.The process parameters,the riveting rate,the riveting rate,the punching angle and the riveting depth,which affect the quality of the rivet-free rivet joint,are set.The influence of the four process parameters on the joint geometry is analyzed by analyzing the change of the joint feature size.(2)Numerical simulation of uniaxial tension of rivet-free riveted joints.A uniaxial tensile simulation model of rivet-free riveted joints was established to study the failure modes of riveted joints under unidirectional tension and analyze the stress and strain of joints with broken joint failure.(3)Analysis of fatigue characteristics of rivet-free riveted joints.A fatigue test simulation model was established in FEMFAT to analyze the fatigue damage distribution of rivet-free riveted joints under three typical conditions:cross-stretching,butt-peeling and lap shearing.The effect of the change of process parameters on the fatigue characteristics of the rivet-free riveted joint was investigated by changing the values of the clearance of the male and female molds,the riveting rate,the draft angle of the punch and the depth of the riveting.(4)Process parameter optimization based on NSGA-II algorithm.The maximum tensile strength during uniaxial tension and the minimum fatigue damage value T under cross-stretching conditions were optimized,and the multi-objective optimization of parameters R_d,v,?and H was carried out.(5)Test verification of the rivet-free riveting forming process.The riveted joints of different riveting speeds were fabricated on the rivet-free riveting equipment,and the characteristic dimension values of the obtained riveted joints were compared with the simulation results to verify the effectiveness of the simulation analysis.