Influence of Groove on Metal Vapour Behavior and Arc Characteristics in TIG Welding of High Manganese Stainless Steels

In arc welding, a groove is often used between metal pieces being welded. In tungsten inert gas welding of high-manganese stainless steels with arc voltage control (AVC), the penetration depth was found to increase with groove wall height. The purpose of this study is to understand the influence of the groove on the penetration depth, mainly through numerical simulation. Spectroscopic measurements were also conducted to validate the simulation. The simulation results showed that when no groove is present, several eddies are formed around the arc column and electrode tip, leading to a recirculating flow pattern. When using a groove, shielding gas introduced from the nozzle flows directly into the arc without forming eddies. In the former case, the metal vapour was transported upwards by the recirculating flow into the arc column and the electrode regions. In contrast, in the latter case, the metal vapour was pushed downward to form a dense metal vapour region over the weld pool and was then swept away horizontally. The arc voltage without a groove is about 1 V lower than that with a groove because the metal vapour around the electrode tip increases the arc electrical conductivity. This affects the arc length control when AVC is used. When the arc voltage increases, the AVC shortens the arc length to keep the voltage constant, leading to the deeper penetration by concentrating the heat input and arc pressure. These mechanisms cause the change of penetration depth when the height of the groove wall is changed.