(A) study on arc plasma analysis in constant and pulsed current gas tungsten arc welding

Abstract

Numerical analysis for an arc plasma in the constant current and pulsed current GTA welding was performed to describe its characteristics. As a boundary condition, the current density distribution and temperature distribution along the electrode surface was emphasized. The current density was assumed to have a Gaussian distribution on the electrode surface. For various electrode vertex angles the distribution parameters were analytically calculated. As a result the calculated temperature contours of arc plasma have been improved much to have a conformity with experimental data. And it has been found that isothermal contours are broadened by using the distributed temperature condition. The effect of the flow rate of shielding gas was reviewed. As the flow rate of shielding gas increases, the high temperature region tend to shrink. The extremely steep pressure gradient was found near the electrode tip. It is assumed that this steep gradient of pressure at electrode tip drives a plasma jet flow to anode plate in a high velocity. The volumetric radiative heat flux was analyzed from the model of an entire free burning arc of GTA welding and the results were compared with the measurements of arc light intensity. The radiation heat increases as the arc length increases. However, the radiation heat does not increase linearly as the arc length increases, because it is largely affected by view factors, $r^2_{i,j}$ and ψ. And eventually the radiation heat increase approaches a certain balanced value between the generated heat increase and the radiation distance (arc length) increase, as the arc length increases. The effect of electrode vertex angle is not so significant in the radiative heat flux and arc light intensity. However, the results of analysis and experiment consistently show that the smaller electrode vertex angle, namely, the sharper cone emits the more radiative heat flux, which is presumed to be resulted from the plasma climb on the electrode surface. The ar...