The influence of arc interactions and a central filler wire on shielding gas flow in tandem GMAW

Abstract

Tandem gas metal arc welding (GMAW) has been developed in order to increase the productivity of the GMAW process and enables rapid joint completion. However, the very small distance between the two arcs and the superposed magnetic fields causes arc interactions and weld pool instabilities, which reduces the process capability. In this article, an advanced tandem GMA welding process is presented, in which a separation of the two arcs is achieved by a centrally fed filler wire. In high-speed recordings and numerical calculations, the arc stabilizing effect by the filler wire is investigated. The geometric boundary of the filler wire separates the arc streams in the flow area and forms a barrier in the weld pool to reduce unfavorable weld pool oscillation. Furthermore, the arc deflection can be influenced via a hot-wire technique and a positive effect is obtained when the hot-wire polarity is opposed to the arc wires. In addition, the deposition rate can also be increased by the resistive preheating of the filler wire. As a result, the process capability and the productivity of the tandem GMAW process are increased significantly. However, it was shown that even with the more stable advanced tandem GMAW process, sufficient shielding gas coverage can only be achieved within a common shielding gas nozzle used in conventional tandem GMAW processes.