Numerical study of arc plasmas and weld pools for GTAW with applied axial magnetic fields

A 3D numerical model containing the welding arc and the weld pool for gas tungsten arc welding (GTAW) with applied axial magnetic fields is established. The model is validated by comparing the calculated arc temperature with the measured ones. The influence of the magnetic field on the welding process is studied by changing the magnetic inductions, from 0 T to 0.06 T. For welding arcs, a radial spread is discovered, and a reverse flow appears over the anode. The distribution of temperature, heat flux, current density and pressure on the anode surface becomes double-peaked, while the voltage distributes in a double-valley type. For weld pools, the fluid flow cycle brings about a wide and shallow pool. In the circumferential direction, the fluid in the centre areas rotates in an opposite direction to that in the outer regions; in the axial direction, the fluid flows upwards at the centre while downwards in the edge area of the weld pool. All the driving forces including the surface tension, the shear stress from the arc plasma, the electromagnetic force and the buoyancy force that influence the fluid flow are analysed to explain these phenomena. The mechanism of how the applied axial magnetic field regulates the GTAW process is thus clarified.