Research On The Forming Law And Mechanical Properties Of Flat Clinching

Lightweight has become the trend of world automobile development.The large-scale application of aluminum alloys has achieved the lightweight of the body,but it has brought new challenges to the existing body joining technology.The rapid development of clinching joining technology provides a new solution for this in recent years.Mechanical clinching is a joining process in which materials are cold deformed,and has been widely used in trunks,hoods,doors and fenders.In order to overcome the defect that a conventional clinched joint has an exterior protrusion on the die-sided sheet,the Chemnitz University of Technology in Germany developed flat clinching process.It has gradually become a research hotspot at home and abroad because it can be applied to functional surfaces and visible areas.In this paper,a systematic and indepth study of flat clinching was carried out.The research contents include its plastic forming process and failure mechanism,the influencing factors of the joint mechanical properties and its action mechanism,as well as the strength improvement method.Based on the ABAQUS software platform,the finite element model of flat clinching was established by the obtained plastic deformation constitutive equation.The evolution law of the internal stress field and strain field in the formation process of the mechanical interlock between the double-layer sheets was revealed through finite element analysis.The material flow behavior during the forming process was obtained by numerical simulation and experimental researches.The fracture of the failed joint was analyzed,and its failure mechanism was revealed,which lays a foundation for the structural design and optimization of the joint.A large number of experimental studies of flat clinching joining were carried out with different influencing factors,including forming force,material,sheet thickness,and blank holder type.The mechanical properties of the joints were evaluated by the tensile shear and cross-tension loads of the joints.Through the analysis of cross-section parameters of the clinched joints,the influencing factors of the joint mechanical properties and its action mechanism were revealed.Multiple finite element models were established based on the finite element method and the response surface method.Finally,the geometric parameters of the joining tools were optimized by genetic algorithm.The strength of the joint obtained after optimization was increased by 13.7%.Auxiliary sheet process and reshaping process were studied to improve the mechanical properties of clinched joints and reduce the protrusion height.The tensile shear load of the clinched joint obtained by the auxiliary plate process was increased by 42.0%.The tensile shear load of the clinched joint obtained by the reshaping process was increased by 24.2%,and its cross-tension load was increased by 8.6%.