Research And Experiment On Magnetic Pulse Welding Method Of Aluminum/Steel Sheets

Lightweight technology is an important way to achieve effective energy conservation,material reduction and environmental protection in many fields such as automobiles,ships,aerospace.On the premise of ensuring the structural strength of the equipment,it is one of the effective means to achieve lightweight by replacing traditional steel with lightweight and high-strength aluminum alloy,magnesium alloy,etc.However,there are significant differences in physical and chemical properties between dissimilar metals,and it is difficult to achieve high-quality welding through traditional fusion welding.Magnetic pulse welding uses pulse electromagnetic force to drive the workpiece to be welded to produce high-speed collision,which can achieve metallurgical combination of dissimilar metals.It has the advantages of high welding strength,no pollution and easy automation.At present,the magnetic pulse welding of dissimilar metal plates mostly uses single-turn wire,and the research is relatively mature.However,this method has the shortcomings of low energy utilization and easy deformation and damage of the wire,and welding with a multi-turn coil structure can effectively overcome these shortcomings.At present,some scholars have carried out relevant experimental research,but there are many deficiencies in welding system modeling and welding performance,and further in-depth research is still needed in the macro and micro characteristics and mechanisms of welding,so as to better guide the design of welding equipment and improve the welding quality.In view of this,the paper took two typical multi turn coil welding methods of field shaper type magnetic pulse spot welding and uniform pressure type magnetic pulse surface welding for aluminum/ steel plate as the object,and carried out systematic theoretical and experimental research from the above three aspects.The main contents and innovations include:In terms of the welding system model construction,the field-circuit combining method for solving the magnetic pulse welding process is proposed.Firstly,the analytical circuit models of magnetic pulse spot welding and uniform pressure surface welding are established on the basis of fully considering the non-uniform characteristics of coil current distribution,which improves the calculation accuracy of existing models and realizes the solution of welding system circuit.Then,the pulse current obtained from the circuit model is introduced into LS-DYNA software as an excitation to establish a three-dimensional collision FEM-BEM model of the welding process,which realizes the field circuit combined calculation of the magnetic pulse welding process,solves the shortage of the existing model relying on the experiment to obtain the pulse current,and provides an effective analysis means for the design and performance prediction of the welding device.In terms of spot welding method research and experimentation,firstly,the influence of coil and field shaper structure parameters on magnetic pressure of magnetic pulse spot welding system is clarified,the spot welding magnet device is optimized,and a flat field shaper structure with arc inner hole surface is proposed.Then,the experimental platform of magnetic pulse spot welding was designed and built,and the welding effects of different inner hole field shapers were compared and verified.The effects of different welding process parameters on joint welding quality were analyzed,the corresponding welding process parameter window was determined,and the high-quality spot welding of AA1060 aluminum sheet and SS304 stainless steel sheet was realized.Finally,the causes of the bulge problem in the center of the welding sample are analyzed,and the influence of the discharge voltage,welding gap and the radius of the inner hole of the field shaper on the bulge size is clarified.A welding method based on the central opening and pre-deformation of the aluminum plate is proposed,which effectively solves the bulge problem in the center of the welding sample.The welding method based on the central opening of the aluminum plate also improves the welding efficiency.In terms of surface welding method research and experimentation,firstly,the uniform pressure magnet devices with different structures are optimized and designed by combining the analytical model with the finite element model.The experimental platform of uniform pressure welding was built,and aiming at the problems of thinning tear and arc ablation at the chamfer of plate in uniform pressure welding,the improvement methods of adding buffer blocks and reducing contact resistance were proposed.Then,the surface welding of AA1060 aluminum plate and SS304 stainless steel plate was realized under different process parameters and structural parameters.Through the tensile test and the analysis of the welding area morphology after alkaline solution corrosion,the effects of welding technology and magnet structure on the welding quality and welding area were proved.Finally,based on the previous research,a uniform pressure welding method based on predeformation is proposed,which effectively suppresses the bulge problem of center non welding and the thinning of aluminum plate at the chamfer in the uniform pressure welding,thus further improving the welding quality of the joint.In the research of plate deformation behavior and interface forming machine,firstly,the macro deformation behavior of the plate in the welding process is analyzed by using a three-dimensional collision model,and the effects of process parameters and structural parameters on the collision speed and angle of the plate are clarified.Then,the smooth particle hydrodynamics model of the welding interface is established by selecting the typical collision velocity and collision angle as the initial conditions in the collision process.The micro deformation behavior of the impact contact interface is analyzed,and the influence of the collision velocity and collision angle on the formation of the composite interface is clarified.Finally,combined with the analysis of the micro interface morphology and microstructure of the magnetic pulse welding joint,the essence of the influence of the welding process parameters and structural parameters on the welding results and the formation mechanism of the waveform composite interface were revealed,and the correlation between the parameters before the magnetic pulse welding,the collision speed and angle during the welding process and the mechanical properties after the welding was established,which provided a basis for the design of the welding device and the adjustment of the welding parameters.