Research On Weld Formation And Vision Sensing During Optical Fiber Laser Welding Of Aluminum To Steel Dissimilar Materials

With the rapid development of society and economy,energy shortages and environmental pollution have become increasingly severe.Reducing the weight of transportation vehicles and realizing lightweight technology for automobiles can reduce energy consumption and reduce the impact on the environment,which is being the focus of attention of the machinery industry,the automobile industry and the transportation industry.Aluminum alloy,which can partially replace steel as structural parts,has the advantages of light weight and good corrosion resistance.Steel has high strength and can withstand large dynamic loads,which can ensure the stability and reliability of structural parts.Therefore,the connection technology of aluminum and steel has become a research central issue However,the physical and chemical properties of the two metals such as the density,melting point and thermal expansion coefficient of aluminum and steel are quite different.The welding process is unstable.Defects such as pores,cracks and depression are prone to occur after welding.And hard brittleness compounds is easily formed at the aluminum-steel bonding interface.Good weld formation is important during the aluminum-steel laser welding.These are the difficulties in aluminum-steel laser weldingFiber laser welding has the advantages of small heat-affected zone,fast welding speed and large aspect ratio.It can better control the energy input and is beneficial to realize the effective connection of aluminum and steel dissimilar metals.However,in the process of laser welding of aluminum and steel,the formation of intermetallic compounds,weld formation and control need to be further studied.Therefore,this article mainly uses fiber laser welding to obtain the aluminum and steel jointsFirstly,the pulse YAG fiber laser welding is performed on the aluminum steel sheet.By designing 24 sets of experimental process parameters,three types of weld formations unfused,fused and welded through are obtained.The olympus microscope is used to observe the local microscopic characteristics of the weld and analyze the connection between energy input and weld formation.The height of the weld is measured by a point displacement laser sensor,and relationship between the height of the weld and the peak power,welding speed,defocus and pulse frequency is analyzed.Then,a high-power continuous laser automatic welding system is used to connect aluminum and steel,and the welding parameters are optimized.The relationship between the weld width,lap shear force,and the welding parameters such as laser power,welding speed and defocus is analyzed.It is found that the combination of laser power and welding speed,even if the laser line energy input has a significant effect on the weld width and lap shear force.The best range of process parameters is obtained through the desired optimization method.For the 2 mm aluminum and steel welding,a welded joint with high strength can be obtained when the laser power is 2.2-2.4 kW,the defocus is 0.27 mm,and the welding speed is in the range of 2.8-3.1 m/min.Secondly,the lap shear strength,weld microstructure and joint fracture mode of aluminum-steel laser welding are studied.And the welding process is inspected online with a high-speed camera.The influence of the laser power,welding speed and defocus on the lap shear strength are analyzed,respectively.Through optical microscope and scanning electron microscope,we observed the weld formation and intermetallic compound with different laser power,and analyzed the two failure modes of the joint.The test results show that the laser line energy input affects the weld formation and lap shear strength.In the fiber laser deep penetration welding mode,both aluminum and steel melt,resulting in an increase in the generation of intermetallic compounds and uneven distribution at the aluminum-steel interface.Moreover,it affects the mechanical properties and fracture modes of the joint.Secondary cracks and needle-like clusters are found in the micrographs of the fracture surface of the joint.Thirdly,laser welding of aluminum and steel with the intermediate layer foil is performed and the influence of adding Cu and Ni foil on the weld formation and mechanical properties is analyzed.Through scanning electron microscopy and energy spectrum analysis,there are three kinds of additions:no addition,addition of Cu foil and addition of Ni foil.The point,line and surface energy spectrum scan of the intermetallic compound are performed at the aluminum-steel bonding interface of the weld join.Finally,the original image of the aluminum steel laser welding process is extracted by image processing technology,and the characteristic parameters of time domain and frequency domain are extracted,respectively.And three characteristic values of metal vapor area,spatter number and area of the tail of the molten pool are extracted.Characteristic parameters are processed through statistical analysis and wavelet packet.Support vector machine is used for modeling.The input of the model is optimized through normalization Grid search,genetic algorithm and particle swarm optimization algorithm are used for parameter optimization to realize the recognition of welding process status.