Numerical Simulation Research On Droplet Transfer Behavior Of Gas Metal Arc Welding

In the traditional gas metal arc welding（CO₂welding and MIG welding），the welding current not only supplies the heat to melt the wire，but also providesthe force to achieve droplet transition, under this condition, the transition canonly be in the form of short-circuit or large droplets. Separating the heat and theforce will realize free controllable metal transfer under low currents within acertain sizes range. So the concept of free controllable metal transfer under lowcurrents with collaborative effect of low-power pulsed laser and negative currentpulse is put forward. As the early part of this study, the force state, the criticalsizes of droplets and the effect of currents under low currents of CO₂weldingshould be studied.As the basic study of metal transfer of low current CO₂welding, this paperuses Surface Evolver—a finite element analysis software and the principle ofminimum energy to make numerical simulation of free metal transfer of MIGwelding. At first, three-dimensional numerical model of MIG welding isestablished, the description of the mechanical model and energy model arecompleted, and the effect of welding current, droplet sizes and the surface tensionare analyzed. On this basis, the behaviors of free metal transfer of CO₂weldingand the effect of the repulse force and the negative current pulse on free metaltransfer are analyzed. The results show that the repulse force existing in the CO₂welding hinders the droplet transfer apparently. When the negative current pulseis appended, the droplet will be changed from being hold state into droop stateand the transition is promoted by it.To illustrate the additional external force through hitting of the low powerlaser, this paper establishes the physical experimental model of additionalexternal force by laser and does the preliminary exploratory experiment. Theexperiments prove that the additional laser produces boiling on the local surface.As a result of that the evaporation reaction force is raised and the metal transferis stimulated.The behaviors of metal transfer under additional force are investigated withnumerical simulation after the additional force applied by laser is confirmed. The critical sizes of droplets will become smaller with the increase of additional force.This situation is more obvious in the early of the additional force, to a certainextent, the critical sizes of the droplets won’t change substantially. It can beobtained that the repulse force will be reduced dramatically even eliminated afterthe negative pulse through the investigation of the effect on metal transfer by thenegative current pulse. When the droplet becomes droop state, the stresscondition of the CO₂welding will be similar to the MIG welding. Under theabove conditions, additional force is able to assist the metal transfer of the CO₂welding as that in the MIG welding and reduce the critical sizes of the droplets torealize the free dropwise transition under the relatively low current.