Study On Incremental Laser Shock Clinching/Welding/Welding-Clinching Of Foils

With the rapid development of modern industry,components and parts tend to be miniaturized increasingly.Therefore,how to realize the connection between foils has become a crucial problem in the fields of materials science.Laser shock forming technology aims to force the foil to produce plastic deformation under the mechanical effect of laser-induced shock wave.Among them,laser shock clinching(LSC)and laser shock welding(LSW)show very significant advantages in the joining between dissimilar thin materials.The former makes interlock structure between materials,the latter makes mechanical and metallurgical bonding between materials.At present,the research on LSC is mainly about circular hole clinching,whose diameter is smaller than that of laser spot.Based on the work,a novel method to expand forming area and manufacture special-shaped joint,named as incremental laser shock clinching(ILSC),is proposed in this paper.Aiming at the issue that the study on LSW is limited to single spot,the research on multiple welding spots by LSW is carried out.A composite connection technology named laser shock welding-clinching is investigated which combines ILSC and LSW.The process parameters,joint structure,mechanical properties,material flow and so on were studied by experimental study and numerical simulation.(1)Research on incremental laser shock clinching.Taking the Cu/Al/Stainless steel(Ss)combination as the research object,experimental and numerical investigation of ILSC was conducted.By observing the morphology and cross sections of round end rectangular joint,the feasibility of ILSC was verified.The study of process parameters showed that enough forming height was needed to form the three-stage interlock structure and the multi-pass forming strategy can improve the formability and surface quality.The tensile test results showed that the clamping mode can affect the joint strength and failure modes while the loading direction only affected the joint strength.The tensile strength perpendicular to the length direction of the joint was always higher than its parallel direction.The simulation results showed that most material flowed along transverse direction to form undercuts,meanwhile flowed slightly towards the laser spot moving direction.The strain distribution of the materials was different,but the maximum strain both appeared in the laser spot overlap area.(2)Research on laser shock welding.Taking the Cu/Cu and Al/Cu combination as the research objects,experimental investigation of single and multiple welding spots by LSW was conducted.The results showed that the smaller the standoff distance was.the better the welding sample with good surface quality can be obtained.When welding multiple points,distance interval was needed to ensure the same forming area of each welding point.Blistering,ablation and fracture were easy to appear in the welding process.The waveform of the welding interface was related to the material combination,and it was not easy to appear flat interface and the waveform was large for AI/Cu.Linear scanning results showed that there was weak element diffusion on the welding interface.The tensile test results showed that the strength of the samples increased first and then decreased with the increase of laser energy or the decrease of laser spot size.The strength of the samples increased with the increase of the number of weld spots.The tensile strength perpendicular to the arrangement direction of weld spots was slightly higher than that along the parallel direction.The tensile failure modes of welding joints were usually edge fracture and center spalling.(3)Research on laser shock welding-clinching.Line undercut structure was formed by ILSC on Cu/Cu single spot welding sample which was obtained first by LSW.Round end rectangular joint with three welding spots of Cu/Al/Ss combination was studied by experiments and numerical simulation.By comparing the microstructure of the welding samples before and after annealing,it was found that the intermediate annealing process made the grain size increase appropriately.However,because of the elimination of hardening,it was beneficial for subsequent forming.Weld spot played a major role for the joint of line undercut structure with single weld spot in the tensile shear tests,whose tensile strength was slightly lower than that of the welding sample,but much higher than that of the line undercut structure.When the upper layer material was clamped on one side alone and stretched along the direction perpendicular to the joint length.the performance of the composite joint was better than that of the clinched joint and the welded joint under the same experimental parameters.The simulation results showed that there was little springback gap between the two forming materials due to the existence of welding spots.The displacements of the material along the transverse and longitudinal directions were both approximately symmetrical and the maximum displacement appeared at the edge of the interlock.The large strain appeared at the neck of interlock,the unconnected area of welding spots and the area around the edge of welding spots.The above research results provide a new way for the connection of metal foils and has theoretical and experimental guiding significance for its industrial application.