Metal vapor-induced arc instability in stationary TIG-welding

Abstract

The stability of the arc in arc welding processes is primarily relevant to the joint quality. However, the influencing factors which determine the arc stability are still partly unknown. Combining arc welding with laser welding enhances arc stability. The laser-induced metal vapor is often named as one stabilizing factor. But this contradicts the presumptions of arc welding researchers who mentioned the metal vapor as a destabilizing factor especially when high amounts are present in the arc. This investigation analyzes the specific influence of metal vapor on arc conductivity as one aspect of arc stability by producing metal vapor using a laser process on a separately placed substrate material. Furthermore, the arc current was varied at a constant metal vapor amount. The investigations show that the metal vapor presence increases the arc voltage by at least 20% and its fluctuation amplitude by at least 51% which was presumed to mean a decreased electrical conductivity and therefore decreased arc stability. The arc instability was lower for higher arc currents at constant metal vapor amounts. Therefore, higher arc currents increase the arc stability of welding arcs in the presence of a constant metal vapor amount.