Study On Forming Defects And Joints Strength Of Microscale Laser Shock Clinching For Dissimilar Materials

Microscale laser shock clinching(μLSC)process is a micro-joining process that uses laser-induced pressure generated by a shock wave to form a mechanical undercut of micro-scale sheets.As a new connection process combining laser shock forming and clinching,μLSC process has the advantages of high efficiency,time saving and high connectivity between dissimilar materials,and has broad application prospects in the field of MEMS component manufacturing.In this paper,the experimental method is supplemented by simulation.μLSC process is studied around initial grain size,height of blocking plate,shock number,laser power density,thickness of upper plate.Through a large number of experiments,two kinds of process windows are established,and the forming pattern of the sample inμLSC process is analyzed.The influence of temperature rise on the forming process during μLSC process was calculated by means of the simulated data.The failure phenomenon of the sample joints in μLSC process were observed by SEM.and the failure mechanism of the connecting plate on the material under high strain rate was analyzed.The effects of different process parameters on the strength of the sample joints in μLSC process were analyzed.The main work and conclusions of this paper are as follows:Two process windows for shock number,height of blocking plate and power density were established,and the forming difficulty with different process parameters was analyzed.The forming pattern of the samples were analyzed around initial grain size,height of blocking plate,laser power density and shock number.The results show that the lowering rate of lower plate at the neck and bottom edge of the sample is easy to produce defects,and the central portion of the connecting plate has the lowest thinning rate.Based on the calculation of temperature rise in laser shock forming,combined with the data obtained from the simulation,the temperature rise in μLSC process was calculated.Three kinds of defects such as uneven joints undercut,bottom rupture and neck rupture were analyzed.The sections of different defects were observed by SEM,and the causes of different defects were obtained.The results show that unevenness of undercut is caused by the unevenness of plastic deformation,and the central crack of the bottom is caused by the residue of absorption layer.The neck rupture is caused by the shearing action of lower plate rounded corners on upper plate.The effects of process parameters including initial grain size,upper plate thickness.height of blocking plate and laser power density on the bottom edge cracking defects were analyzed.As initial grain size increases,the difficulty in forming undercut of the sample is reduced,but the degree of cracking of the defect increases.As thickness of upper plate increases,the degree of defect cracking decreases.As the laser power density increases,shock number that achieve effective undercut decreases,but the degree of cracking of the defects increases.The shear strength of sample joints in μLSC process was tested experimentally.LUltra-depth microscopy and SEM were used to observe the failure morphology of joints under different process parameters.Experiments show that pull-off failure of joints is affected by the yield streng,th and undercut value of the joints.Crack failure of joints are generated by lower plate rounding shearing action,and then extended to the substrate by the tensile force.