Numerical simulation of fume formation process in GMA welding

In order to clarify fume formation process in GMA welding, quantitative investigation based on understanding of interaction between the electrode, the arc, and the weld pool is indispensable. This study aims to clarify the fume formation process theoretically through numerical analysis. A fume formation model consisting of a homogeneous nucleation model, a heterogeneous condensation model, and a coagulation model was coupled with a GMA welding model. A series of processes such as evaporation of metal vapor from molten metal, transport of the metal vapor in the arc, fume formation from the metal vapor, and transport of the fume to the surrounding was investigated by employing this coupled simulation model. In this paper, the influence on the fume formation process of changing the shielding gas from Ar to CO2 and the associated change in arc characteristics, leading to different droplet formation and metal transfer phenomena, is discussed. As a result, it was clarified that the fume particles produced around the droplet were transported into the arc to be evaporated again and a large number of fine fume particles were produced in the downstream region of the plasma flow near the base metal in Ar GMA welding. In contrast, approximately 30% of all fume particles produced around the droplet were transported directly to the surrounding and the other particles were transported into the arc to be evaporated to produce fume particles in the downstream region in CO2 arc welding.