Numerical analysis of weld pool formation mechanism in TIG welding in consideration of the influence of emitter material adding to the tungsten cathode

Abstract

Generally, ThO2 or La2O3 are added to a tungsten cathode for prompting electron emission from the cathode and preventing the cathode from consumption. In this study, influence of adding 2%ThO to the tungsten cathode as emitter material on arc properties and weld pool formation mechanism in TIG welding was investigated by employing numerical simulation model considering heat and mass transfers among the cathode, the arc and the weld pool. As a result, it was found that although the maximum cathode jet velocity in case of 2%ThO2-W cathode was 497 m/s, that in case of pure W cathode was only 156 m/s because of low current density caused by flatten surface of the melting cathode tip. In case of 2%ThO2-W cathode, the depth and the width of the weld pool became shallow wide than those in case of pure W cathode. For a reason, it is considered that because shearing force from the arc to the weld pool was larger than that of pure W cathode due to higher cathode jet velocity, the heat transport in the weld pool near the surface in radial outward direction increased