3D non-axisymmetric numerical analysis of droplet oscillation, arc drifting and molten pool evolution for underwater wet FCAW

In this work, a 3D non-axisymmetric numerical model for underwater wet flux-cored arc welding (UW-FCAW) of Q235 steel was developed, which simultaneously coupled the arc, droplet and molten pool. The droplet deviation, rotation and oscillation behaviors of the globular repelled transfer mode, the arc cathodic drifting behavior as well as molten pool evolution were simulated. A more complete force source model for numerical calculation of the metal transfer was proposed, which considered the expansion force of the gas released from the flux-core and the drag force of the gas flow inside bubbles. Meanwhile, the influence of welding current on the welding process was considered. It was found that due to the rotation of droplets, the arc drifts at the cathode surface, causing the concave deformation of the molten pool rotate as well, forming a stirring effect on the molten pool. Moreover, the deviation and detachment angle of droplets increase with the welding current, with a maximum deviation angle of 103 degrees at 150 A, 120 degrees at 200 A and 145 degrees at 250 A respectively, which means a greater chance of spatter generation. The melt width and penetration are also positively correlated with the welding current, with 13.72 mm/1.45 mm at 150 A, 16.48 mm/2.26 mm at 200 A and 18.04 mm/2.76 mm at 250 A respectively. To verify the reliability of the model, UW-FCAW experiments and visual sensing were carried out, the simulation results were found to be in good agreement with the experimental ones.