Numerical analysis of the behavior of molten pool and the suppression mechanism of undercut defect in TIG-MIG hybrid welding

Abstract

In order to investigate the multi-coupling transport phenomena in TIG-MIG hybrid arc welding, a three-dimensional model including droplet and molten pool was established. An innovative distribution pattern of arc heat and force that adapted to the evolution of molten pool surface was proposed, achieving a unified distribution of "arc current density-arc pressure-electromagnetic force-arc heat". The effect of TIG arc on molten pool behavior and undercut defect was quantitatively analyzed by comparing TIG-MIG hybrid welding with traditional MIG welding. The results showed that the electromagnetic repulsion between the two arcs with opposite currents increased the aspect ratio of the hybrid arc heat and force distribution. It led to a long and narrow gouging region, where the promoting effect of inertial force on the undercut was weakened by arc pressure and hydrostatic pressure. The liquid metal with a lower cooling rate had sufficient time to fully fill the weld toe and suppressed undercut. Sensitivity and dimensional analysis illustrated that the TIG-MIG hybrid arc eliminated undercut by reducing the inertia force, adjusting the arc pressure distribution, and enhancing the hydrostatic pressure. The groove sizes was predicated based on molten pool characteristics, including the stress state of liquid metal, morphology, and fluid flow patterns. It revealed the quantitative relationships among welding parameters, behavior of molten pool, and weld bead formation, promoting the implementation of digital twinning technology in the manufacturing industries.