TIG arc characteristics in different atmospheres (part 1)

Summary

The physical properties of gases such as density, thermal and electrical conductivity, as well as ionisation potential, determine to a great extent the operational characteristics of welding arcs. These properties may vary widely for different gases. As a result, arc voltage, heat output, mean radius, thermal profile, performance and other parameters which influence bead geometry (shape, width and penetration) depend on the chemical composition of the shielding gas. Rather complex physical models have been proposed to explain and quantify the effects of shielding gas chemical composition on welding arc performance. The influence of arc atmosphere may also be easily predicted by empirical methods. However, only changes in arc operational parameters and weld bead geometry due to variations in gas composition appear in the literature. This article presents an optical study of the TIG welding arc, based on a digital system of image capture and welding parameter recording, during arc operation. Variations in arc aspect, dimensions and electrical parameters were observed, and the results related to the physical properties of gases and mixtures used, as well as forecasts by theoretical models.