Study On Mechanism And Joint Quality Optimization Methods Of Hole-clinching Process

With the depletion of petroleum resources,the increasing demand for energy saving and emission reduction in automobiles,automobile lightweight has gradually become a common concern for automobile companies.The use of lightweight materials and connection technology is an effective way to achieve automobile lightweight.With the increasing proportion of high-strength steel and aluminum alloy used in automobile bodies,realization of the effective connection of aluminum plates and high-strength steel plates has become a hot spot for more and more scholars.In this paper,the hole-clinching process of 5052 aluminum plate and HC420LA high-strength steel plate is used to study the connection forming mechanism,the influence of structural parameters and the optimization design of die structure.The main study contents and conclusions are as follows:The axisymmetric simulation model of hole-clinching process was established by ABAQUS.The load variation,the stress and strain state,the deformation mechanism and the influence of the bottom thickness on the joint geometry during the connection process were studied.According to load variation during the connection process,the connection process can be divided into elastic deformation stage,free deformation stage,compression deformation stage and interlocking stage.The upper plate undergoes bending,stretching and extrusion deformation during the deformation process,and the lower plate is substantially not deformed.The connection joint is finally formed.At room temperature,5052 aluminum plate and HC420LA high-strength steel plate were subjected to a tensile test to obtain mechanical properties.Then,the influence of the main mold factors,such as punch fillet radius,punch radius,punch draft and spacer height on joint forming,were explored by simulation analysis.The results show that as the punch fillet radius increases,the thickness of the joint neck increases and the interlock value decreases.As the punch radius increases,the thickness of the joint neck decreases,but the interlock value increases.The joint forming quality is poor while punch radius is too large,and in this case the sheet is easily broken.As the draft of the punch increases,the thickness of the joint neck decreases,while the interlock value increases.However,there is no significant change in the joint geometry.As the spacer height increases,the joint geometry decreases,and meanwhile the connection load changes greatly.The mold structural parameters were optimized by orthogonal experimental design,response surface method and multi-objective genetic algorithm based on Pareto solution.The mold structural parameters,including punch fillet radius,punch radius,punch draft and spacer height were used as optimization variables,and the neck thickness and interlock value of the joint were used as evaluation indexes.Firstly,the orthogonal experimental design results were analyzed by range analysis and variance analysis.It is found that the influence of punch radius on neck thickness and interlock value was the most significant.Then the functions of the neck thickness and the interlock value were obtained through the central composite design.Using the multi-objective genetic optimization based on Pareto solution,the mold structural parameters were optimized.The optimal mold process parameter combination is 2.0mm in punch fillet radius,3.6mm in punch radius,and 1.0mm in spacer height.The hole-clinching process mold is designed and manufactured according to the optimum parameters of the mold.The cross-sectional dimension measurement and shear test were performed on the joint samples obtained by the experiment.The accuracy of the above established simulation model is verified by the experimental results in terms of the section geometry and load.Joints performance test results show that the failure mode of the joint during the shearing process is shear failure.Furthermore,the increase of the joint neck thickness is beneficial to improve the joint load,failure displacement and joint energy absorption capacity,and thus improve the joint quality.