Study On Laser Shock Clinching Of Similar Or Dissimilar Metal Foils

With the development trend of lightweight in industry,the coupling of various materials is necessary in the manufacturing process of parts,so a higher requirement is put forward for joining technology based on plastic deformation among various materials.Serving as a new combination of laser shock forming technology and mechanical clinching technology,laser shock clinching(LSC)aims to force the target foils to produce plastic deformation under the mechanical effect of laser induced shock wave,so as to realize the mechanical connection between multi-layer ultra-thin sheets in the micro-scale.Based on the previous study of LSC of single-layer copper foil and perforated stainless steel sheet,this paper explores the LSC of similar or dissimilar foils,and finally realizes the clinching of double metal foils and perforated stainless steel sheet.Pulsed laser induced plasma is used to form a high-pressure shock wave to drive the metal foils to produce a specific plastic deformation,forming an embedded interlocking structure,and achieving the ultimate clinching of the ultra-thin sheets at a micro scale.In this paper,the LSC technology for joining double foils and a perforated stainless steel sheet is studied from three aspects:numerical simulation,feasibility and parameter experiment,as well as mechanical properties.The main work and conclusions are as follows:(1)Numerical simulation research.Taking the Cu/Cu/Ss combination as the research object,the numerical simulation study of the LSC forjoining double foils and perforated stainless steel sheet is developed,and the theoretical possibility of this clinching process between the multi-layer sheets is preliminarily determined.By establishing and solving the finite element model of LSC process,the evolution of material geometry,plastic flow and joining mechanism are revealed,and the influence of main process parameters(laser energy and forming height)on the deformation characteristics of clinching is also studied.The difference in the effective plastic strain and thickness reduction properties of two metal foils is largely due to the different propagation and diffusion of the laser-induced shock wave across the two foils.(2)Feasibility and parameter experimental study.This paper firstly studies the feasibility of clinching for four different material combinations,respectively,including the similar foil combinations(Cu/Cu/Ss and Al/Al/Ss)and the dissimilar foil combinations(Cu/Al/Ss and Al/Cu/Ss).By observing the cross sections of joints in four different material combinations,the feasibility of LSC in realizing the connection of various kinds of material combinations can be preliminarily verified.Typical joining defects and failure modes during the LSC process for double metal foils and a perforated stainless steel sheet are analyzed,which mainly consists of no interlocking,neck fracture and bottom fracture.Neck fracture is more likely to occur in the lower foil,and the upper foil tends to fail at the bottom.In order to observe the joining results under different processing conditions,process windows of material combinations are made,which can provide valuable reference for practical processing and application.(3)Research on mechanical properties of clinched joints.For a joining method,the mechanical strength of joints is an important evaluation criterion for the joining performance,and the tensile shearing test is an effective means to measure the joining strength and failure modes of joint samples.The process parameters and material properties affect the interlocking structure of the joints,and the interlocking structure also determines the mechanical properties of the joints.By analyzing the material flow of joint section and measuring the key interlocking structural dimensions,the effects of laser energy,pulse number and material properties on the interlocking structure are studied.As the laser energy or pulse number increases,the interlocks of joints gradually increase while the neck thicknesses decrease.The material properties has a great influence on the interlocking structure of clinched joints.Even under the same processing conditions,the size of interlocks in Cu/Al/Ss combination is larger than that in Cu/Cu/Ss combination.while the trend of neck thickness shows the opposite.The results of tensile shearing tests show that the mechanical strength and failure modes of joints are greatly affected by the interlocking structure.Only the joints have larger interlocks and neck thicknesses can they achieve higher joining strength.This study provides a new approach to plastic joining for the mixed use of various materials.The LSC technology can realize the clinching between the similar or dissimilar foils and the perforated stainless steel sheet,and can guarantee the high surface quality of clinched joints,this technology also has a broad application prospect at the same time.