Additive assisted through the arc sensing during gas tungsten arc welding

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Abstract
This paper concerns a novel approach to through the arc position sensing, which is based on the influence that certain additives have on the physical behaviour of the welding arc. The changes in the physical behaviour are reflected by changes in arc parameters, in particular arc voltage, which can be monitored during the welding process. In the first part of the paper the results of bead on plate experiments aimed at determining the influence of different additives on arc voltage are presented. Of the different additives considered, SiO2 is found to have the most pronounced effect. It appears that addition of SiO2 results in a voltage increase in the range 1–3 V, depending on arc length, welding current, and travel speed. The observed effect is ascribed to arc contraction and arc trailing. The influence of SiO2 on the weld bead geometry and the mechanical properties of the weld was also determined. It appears that the addition of SiO2 results in enhanced weld penetration, presumably as a result of the observed arc contraction. The results of hardness measurements carried out on transverse cross-sections of the welds indicate that the mechanical properties of the weld are not significantly affected by the addition of SiO2. Preliminary experiments show that the effect of SiO2 on arc voltage can be used as a tool for position sensing and, hence, for seam tracking during gas tungsten arc (GTA) welding.

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