Study On Fine Modeling And Mechanical Properties Of Self-piercing Riveting Joint Of Vacuum Die Casting Aluminum Alloy

Automotive lightweight has become an inevitable trend in the development of automotive industry.In recent years,advanced lightweight materials such as aluminum alloy and high strength steel are more and more widely used.With the progress of manufacturing technology,steel-aluminum hybrid body will be the mainstream technical route for the development of new energy vehicles in the future.Different from the traditional resistance spot welding connection of steel body,the steel-aluminum hybrid body adopts a large number of new connection methods such as self-piercing riveting(SPR),rivetless connection(Clinching)and hot melt tapping(FDS),among which SPR is the most widely used.Under the collision condition,the riveted joint is prone to cracking failure,which affects the deformation mode and collision energy absorption of the body,and puts forward new challenges to the safety design of body collision.Therefore,the establishment of SPR high-precision simulation model to explore the deformation behavior and failure mode of riveting joints is of great significance to quickly optimize the mechanical properties of joints,reduce the workload of experimental tests in the early stage of vehicle development and reduce development costs.In this paper,the SPR joint of AC43500-T7 vacuum die casting aluminum alloy 2.6-2.6mm plate combination is taken as the research object.The construction model and failure parameter calibration of vacuum die casting aluminum alloy material are carried out by combining experiment and simulation.The fine simulation model of SPR joint is constructed,and the deformation behavior and failure mechanism of the joint are explored.SPR forming simulation was used to study the influence of different process parameters on the morphology characteristics of the joint.Combined with the fine simulation analysis of the joint,the relationship between the riveting process and the mechanical properties of the joint was explored,and the combination of riveting process parameters that can improve the mechanical properties of the joint was obtained.Firstly,the Swift-Hockett-Sherby weighted hardening criterion was used to describe the strain hardening characteristics of cast aluminum materials.The MMC equation was used to fit the stress triaxiality and fracture strain curves of cast aluminum materials.The GISSMO failure criterion was selected to simulate the instability and failure behavior of cast aluminum materials in the necking stage.The average error of simulation prediction of peak load and failure displacement of specimens under different stress states is about 5 %,which verifies the simulation accuracy of constitutive model and failure parameters of cast aluminum material for material deformation and failure behavior.Then,the section characteristics of the riveted joint were obtained through experiments.The 3D software was used for reverse modeling.The solid element was used to finely divide the grid of the riveted center area.The constitutive model and failure parameters of the cast aluminum material were calibrated above,and the fine finite element model of the self-piercing riveted joint was established.The mechanical properties and failure behavior of self-piercing riveted joints under three working conditions of drawing °,45° and shearing were analyzed in detail by using this model.Among them,the peak load under shear condition is 6KN,and the failure mode is tearing failure of the lower plate.The peak load of drawing and 45 ° is about4 KN,and the failure mode is tearing failure of upper plate.Thus,the mechanical properties and failure modes of riveted joints under shear conditions were determined as the main optimization objects.Finally,Simufact.Forming software was used to simulate the forming process of riveted joint,and the formation mechanism of joint geometric morphology was studied.It was observed that the rivet size and die size were the key process parameters affecting the geometric morphology and joint performance.The orthogonal test was designed with the process parameters such as rivet size and die size as variables,and the shear strength and morphology characteristic parameters of joints as evaluation indexes.The optimal process scheme was obtained through data analysis.Under the combination of double-layer 2.6 mm cast aluminum alloy sheet,the optimal combination of riveting process parameters is as follows : rivet length7.5 mm,rivet leg diameter 5.3 mm,die depth 1.4 mm,die diameter 12 mm.After optimization,the combined peak load of riveting process parameters increased from 6 KN to 6.6 KN,and the failure displacement increased from 4.1 mm to 6.25 mm.