Analysis Of Droplet Transfer Behavior In CO₂ Laser-MIG Hybrid Welding Process

In the previous work, the droplet drifts towards laser beam due to the effect of the laser plasma and the metal vapor in the CO₂ laser-MIG hybrid welding process, which decreases transfer frequency and breaks transfer stability. As a result, the weld appearance is bad and weld penetration is shallow. Aiming at the change of the stable welding region by laser in hybrid welding process, the influence of laser on transfer behavior and droplet transfer stability was studied by using the FEM software Surface Evolver, and the critical welding condition needed in hybrid welding was obtained.In this paper, the proper assumption and the numerical description of droplet transfer and stress were established by analysing mechanical behavior of droplet transfer in hybrid welding process. Basing on force model and energy control equation, the influence of main parameters, such as, welding current, laser power and shielding gas flow on droplet shape, transfer stability and transfer frequency, were obtained by simulating of droplet transfer shape in laser-MIG hybrid welding process according to the least energy principle and the associated rules of FEM software-Surface Evolver. And the research results show a good accordance between the numerical simulating and the practical technological experiment.The results of computation show that, augment of as laser power and welding current in hybrid welding process, the critical additional axial acceleration of metal transfer would increase or decrease. And the additional axial acceleration and the centroidal offset were brought forward to describe the frequency and stability of droplet transfer. The results show that the additional axial mechanical force may effectively promote the droplet transfer, increase the droplet transfer frequency and the process stability, which proves in theory that it is an available approach to achieve stable droplet transfer by exerting a certain additional axial mechanical force on droplet, and therefore explains the mechanism which can effectively improve the welding stability by increasing shielding gas flow in CO₂ laser-MIG hybrid welding process. Finally, the threshold flow of shielding gas which promotes the droplet to arrive at a critical...