The Numerical Simulation Of Metal Transfer In MIG Based On Magnetron-welding Technology

The shape and energy distribution of welding arc, shape of droplet and metaltransfer modes not only has important impact on the feasibility of welding procedure,but also affects the heat distribution in welded workpiece, closely related withwelding quality, such as welding process stability, microstructure and mechanicalproperty of weld joint, welding residual stress, and so on. Also, the shape of droplet,metal transfer modes and droplet transfer frequency determines the weld sufacesmoothness, weld formation and welding spatter. Control the welding arc shape,energy distribution and process of droplet transfer is one of the most importantapproaches via which magnetron-welding technology improving welding quality. It issignificantly important to monitoring and analyzing welding arc and droplet transferprocess, in order to explaining the mechanism and application expansion ofmagnetron-welding technology.Based on this reason, the high speed camera system was used to observe andcontrast welding arc shape and droplet transfer process in MIG welding underdifferent external longitudinal DC magnetic strength. Meanwhile, this paper establishthe mathematical model of magnetron-welding process based on CFD softwareFLUENT. The influence rules on MIG welding arc and droplet transfer by externalmagnetic fleld was investigated by using numerical simulation along with technologytest.The mathematical model of magnetron-welding arc was established withhydrodynamics and electromagnetic principle. The secondary development ofFLUENT with UDF, which is used to compile the governing equations and relatedsource terms, simulates the velocity, temperature, and preesure distribution in MIGwelding arc under longitudinal DC magnetic field. The polynomial model fitting forarc pressure distribution by MATLAB software, was used to realize the force modelof welding droplet, and then, combined with the Navier-Stokes Equations, to finishthe dynamic model of magnetron-welding droplet. In this model, the ContinuumSurface Tension (CSF) model and Volume of Fluid (VOF) method was used todispose the surface tension on droplet and track-rebuild the free surface of weldingdroplet. Results of the dynomic model shows the shape change and velocity distribution of droplet in the welding metal transfer process with and without externalmagnetic field.The simulation results are consistent with the experimental results, under suitablelongitudinal DC magnetic strength, the welding arc assumes bell-shaped, uppercontraction and lower expansion; the arc temperature and plasma speed is rise slightly,arc pressure reduce on the middle and protrude on the ends, and varies from Gaussiandistribution to “Twin Peaks” distribution. Meanwhile, the welding droplet assumesoblate spheroid and rotating around its own axis, also with the increase of dropletdiameter, the droplet height reduced and droplet transfer frequence decreased. Lastly,this paper analyzes the reasons for these changes, has a certain guiding significance toreveal the mechanism of magnetron-welding technology.