Research On The Micro Clinching Of Metal Foils With Cutting Process By Laser Indirect Shock Forming

With the rapid development of biomedical devices and micro-electromechanical systems,the precision and miniaturization of products has become a trend in the development of industrial manufacturing.During the manufacturing process of precision micro-equipment,the use of dissimilar lightweight materials is required.Therefore,an efficient micro joining technology which can be used to connect dissimilar materials is urgently needed.Based on the laser impact forming technology and the mechanical clinching technology,this dissertation presents a novel micro clinching with cutting by laser indirect shock forming process.It can be used to join the similar and dissimilar materials in the micro scale and expand the application scope of the joining process which is based on the plastic deformation of materials.In this process,the pulse laser is used to replace the traditional micro punch and the soft punch is used as the transmission medium of the impact pressure.The main research work and achievements are as follows:Firstly,the mechanism of the interaction between laser and material is investigated,and the mathematical model of the peak pressure is established.The plastic deformation yield condition of the material under high strain rate and the impedance matching between the soft punch and the workpiece is discussed.The formation process of the joints and the connection mechanism of the traditional clinching with cutting technology are studied.Secondly,a series of experiments are conducted to verify the feasibility of micro clinching with cutting by laser indirect shock forming process for joining similar and dissimilar metal foils.The experimental results show that the large interlock cannot be formed under single laser pulse,however,the use of multiple laser pulses and the moderate energy can solve this problem.There is a certain matching relationship between the total thickness of the materials to be connected and the die depth.With the increase of the total thickness of materials,the corresponding die depth that can form a large interlock increases.According to the process window of different material combinations,this novel process is more suitable for joining the material combination where the upper sheet is thicker than the lower sheet.With the increase of laser energy,the interlock between the metal foils increased while the minimum thickness of the upper foil gradually decreased.Under the same condition of the sheet thickness,the tensile strength of the Al/SS combination is the highest,which is about three times larger than that of the Al/Cu and the Cu/Cu combination.Thirdly,the applicability of this novel process on the thick metal foils is verified by using a laser with larger laser energy.The experimental system of the micro clinching with cutting by laser indirect shock forming process is improved.In addition,the influence of process parameters on the mechanical behavior of clinched joints is investigated.The effect of the neck thickness of the upper sheet and the interlock on the tensile strength and corresponding failure models is discussed by means of the single lap shearing tests.The changes of the nano-hardness around the joint of the upper and lower metal foils were measured by the nano-indentation experiments.The experimental results show that the thickness of the ablative layer has a great influence on the material flow and the formation of the interlock.In the experiment,the optimum thickness of ablative layer can be selected according to the laser energy.Compared with the remaining thickness of the soft punch,the one with the thickness of 100μm is more suitable for the micro clinching with cutting process;When the thickness of single layer metal foil is less than 200μm,the optimum die depth of the process can be obtained by adding the 80% of the upper sheet thickness to the thickness of the lower sheet.The tensile strength and failure model of the joint depends on the neck thickness of the upper sheet and the interlock.The nano-hardness of the material around the joint is improved by the laser shock,and the greater the plastic deformation of the material is,the higher the corresponding nano-hardness will be.This study provides a new way for the joining of metal foils in the micro scale and lays a theoretical basis for the further application.