Modelling of metal vapour in pulsed TIG including influence of self-absorption

Abstract

Pulsed TIG (tungsten inert gas) welding is used to improve the stability and speed of arc welding, and to allow greater control over the heat input to the weld. The temperature and the radiation power density of the pulsed arc vary as a function of time, as does the distribution of metal vapour, and its effects on the arc. A self-consistent two-dimensional model of the arc and electrodes is used to calculate the properties of the arc as a function of time. Self-absorption of radiation is treated by two methods, one taking into account absorption of radiation only within the control volume of emission, and the other taking into account absorption throughout the plasma. The relation between metal vapour and radiation power density is analysed by calculating the iron vapour distribution. The results show that the transport of iron vapour is strongly affected by the fast convective flow during the peak current period. During the base current period, the region containing a low concentration of metal vapour expands because of the low convective flow. The iron vapour distribution does not closely follow the current pulses. The temperature, iron vapour and radiation power density distributions depend on the self-absorption model used. The temperature distribution becomes broader when self-absorption of radiation from all directions is considered.