Numerical Analysis Of Arc-droplet-pool Behavior In TIG-MIG Hybrid Welding

TIG-MIG hybrid welding can combine the respective advantages of TIG arc and MIG arc to obtain high-quality weld joints at a higher welding speed.There is a complex coupling effect between TIG arc and MIG arc,which has an important impact on the thermo-mechanical behavior of the hybrid welding process.Although the results are real and reliable,it is difficult to quantitatively describe the heat and mass transfer behaviors in the welding process studied through process experiments.However,the numerical simulation of the hybrid welding process mostly analyzes one or two factors of arc,droplet,and molten pool,which cannot deeply reveal the coupling behavior of the three,and also ignores the influence of metal vapor on the welding process.Therefore,this study adopts the method of combining numerical simulation and process experiment to compare and analyze the influence of metal vapor on the arc shape and droplet transfer of TIG-MIG hybrid welding,and summarize the thermal behavior of hybrid welding arc,droplet and metal vapor distribution under different process parameters.It has important scientific research significance and practical value to reveal the coupling mechanism of hybrid welding arc,droplet and molten pool.This research was based on the TIG-MIG hybrid welding process experiment platform.A high-speed camera was used to collect the arc shape and droplet transition,and a CCD colorimetric temperature measurement system was built and calibrated to restore the temperature field distribution of the TIG arc and the MIG arc during hybrid welding,providing data support for the numerical model;a three-dimensional model of the TIG-MIG hybrid welding arc-droplet considering metal vapor was established,and the temperature field,flow field,electric field,and force field were compared and analyzed,revealing the behavior of metal vapor on the hybrid welding arc-droplet.The results showed that the metal vapor would increase the radiation heat dissipation of the plasma,reducing the central electric conductivity of the MIG arc,and increase the current flow between the two electrodes.When the TIG current increased(80 A-120 A),the metal vapor content around the droplet decreased,the current flow between the two arcs increased,and the preheating effect of the TIG arc on the workpiece was significantly improved.With the increase of the inclination angle of the TIG torch(60°-90°),the mass fraction and diffusion trend of metal vapor in the arc space increased,and the plasma flow force on the droplet and the workpiece increased.When the TIG inclination angle was less than 75°,the distribution of the current density on the workpiece was more favorable for the formation of the molten pool.Increasing the filament spacing(5 mm-9 mm)would reduce the coupling effect between arcs and weaken the diffusion tendency of metal vapor in the arc space.When the torch spacing increased to 9 mm,the coupling effect between arcs almost disappears.A three-dimensional model of arc-droplet-weld pool for TIG-MIG spot welding considering metal vapor was established,and the coupling mechanism of arc deflection,droplet transfer and weld pool evolution was analyzed.The deformation of the molten pool surface changed the flow direction of the high-temperature plasma above the molten pool,which affected the temperature in the arc space and the current density distribution on the molten pool surface.As the droplet grows and fell off,the physical fields in the arc space periodic changed.The molten drop falling into the molten pool causes the molten pool to oscillate,which changed the electric field and flow field distribution on the surface and inside of the molten pool,and changed periodically as the molten drop fell into the molten pool-the molten pool oscillated-the molten pool turned stable.The calculated MIG arc,droplet deflection angle and droplet transition frequency were in good agreement with the experimental results;the arc temperature field was compared with the CCD temperature measurement results,and the temperature distribution trend was basically the same;the TIG-MIG fixed-spot welding experiment was carried out,and the experimental results were in good agreement.The trend of seam fusion line was roughly the same as the simulation results,which could show the reliability of the numerical model in this paper.