Laser Indirect Impact Welding Experiment And Numerical Simulation Research

With the rapid development of micro-electromechanical and medical instruments industry,micro-devices are widely used in sensors,robots,unmanned aerial vehicle(UAV),biological medical and other fields.In the manufacturing process of micro-devices,it is often involved in the welding of components with light,thin,short and small features,so micro-manufacturing industry urgently needs reliable and efficient micro-welding technology.This dissertation presents a novel micro-welding method,namely laser indirect shock welding(LISW)and explores the applicability of LISW technology in two welding forms: metal wire/metal sheet,metal sheet/metal sheet.LISW technology is studied by combining experiment and numerical simulation.The main research content and research results of this dissertation are as follows:First of all,two combinations of Al sheet/Cu wire and Al sheet/Ag wire were welded by LISW process and the difference of welding quality between direct shock welding process and indirect shock welding process was compared.The characteristics of the welding interface were observed and analyzed by scanning electron microscope(SEM)and X ray spectrometer(EDS).The change of microhardness at the welding area was measured by the nanoindenter.The tensile shear strength and failure modes of the welded specimen were studied by tensile shear test.The experimental results show that compared with laser direct action on Al sheet,laser indirect shock welding can ensure high surface quality of Al sheet.With the increase of laser pulse energy,the welding area between metal wire and metal sheet is increased.The welding interface is mainly straight or small wave.In addition,there is a short element diffusion layer at the welding interface,and no intermetallic compound is found at the welding interface.As the distance from the welding interface decreases,the microhardness gradually increases.There are two failure modes in the tensile shear test and they are interfacial failure and failure through wire,respectively.Secondly,LISW process was applied to achieve the welding of Al sheet/SS sheet.The difference between Al/SS and SS/Al in terms of weldability and welding interface was compared to determine which material was used as flyer plate and which material was used as base plate.The interface morphology and element distribution of the welded specimens were studied by SEM and EDS.The mechanical strength and failure modes of tensile shear test and peeling test were analyzed by electronic universal testing machine.It is found that the welding performance of Al/SS is better than that of SS/Al.In the experiment,the parameters of laser pulse energy and standoff distance have important influence on the welding quality and there is a certain matching relationship between these two parameters.In addition,the wavelength and amplitude of the interface wave increase with the increase of laser pulse energy.Whether in welding combination of Al/SS or in welding combination of SS/Al,there is a wave characteristic that the direction of wave peak on the side of Al with smaller density is opposite to the welding direction,while the direction of wave peak on the side of SS with larger density is consistent with the welding direction.EDS analysis shows that there is an element diffusion layer with thickness of 4.5?m in the Al/SS welding interface and no intermetallic compound is found at the interface.In the tensile shear test and peeling test,there are all two failure modes: interfacial failure and fracture failure at the edge of welded spot.Thirdly,the welding process of Al sheet/SS sheet is numerically simulated by using AUTODYN software and smooth particle hydrodynamic(SPH)algorithm.Simulation results show that impact velocity and standoff distance have important influence on the morphology of welding interface.When the standoff distance is fixed,with the increase of the impact velocity,the welding interface changes from flat to micro-wave and finally to a wavy interface with micro-vortex.When the impact velocity is fixed,with the increase of the standoff distance,the morphology of welding interface shows a similar changing trend.The characteristic and formation mechanism of the interface waveform are studied and its fundamental reason is the penetration of the jet consisting mainly of low density material.In addition,LISW has the characteristics of high speed,high pressure and high temperature,and there is strong plastic deformation between flyer plate and base plate.This research provides a new way for micro-welding in micro-devices.LISW can guarantee high surface quality of weldment,obtain micro-welding between dissimilar material combinations with very different melting points and can limit the generation of intermetallic compound and heat affected zone in the welding area to the greatest extent.Therefore,it has a very high prospect of industrial application.