Imaging spectroscopy for transient transport of chromium vapor during helium tig welding

The transient transport process of the chromium vapor during Tungsten Inert Gas (TIG) welding was revealed by imaging spectroscopic analysis. During TIG welding, the metal vapor generated from the weld pool surface is transported to the arc plasma. The metal vapor affects the plasma properties such as electrical conductivity and radiation coefficient. However, the transient transport process of the metal vapors including ions inside TIG arc plasma has not been clarified. In this paper, the experiments were performed under the special conditions such as helium TIG welding on pure chromium. After the arc ignition, the chromium vapors were generated from a pure chromium base metal and transported through the inside of the arc plasma to the tungsten cathode. As time passed, the He I spectral intensity gradually decreased. In contrast, the Cr I and Cr II spectral intensities gradually increased near the weld pool, near the electrode and the intermediate region. At a certain time, the chromium vapor reached the center of the arc plasma when using an electrode with a flat tip. The metal vapor distribution inside the arc plasma transiently changed when the plasma flow slowed down due to the electrode deformation during TIG welding.