One of the main advantages of the MIG/MAG process is its high productivity. Usually, the positive polarity is employed, due to a higher arc stability, less spattering and adequate bead profiles. However, a higher production capacity than observed in the conventional MIG/MAG process has been demanded for some applications. In the current literature related to MIG/MAG, it is mentioned that the negative polarity provides a higher fusion rate than the positive one, despite of leading to higher spattering and bead misshapen. Unfortunately, there is no much information available about the effects of process variables in this polarity, as much as concerning justifications. Thus, in this work was attempted to understand the reasons for a higher fusion rate at CC-, as well as the respective effect on the bead geometry. For that, MIG/MAG comparative welds were carried out at both polarities, using two shielding gas blends and two current values. The transfer mode and arc behavior were assessed by synchronized shadowgrafy technique. The bead geometry was evaluated through metallographic procedures. From the results, which does not agree entirely with the current literature, it was observed that as much the transfer mode as the bead morphology and finish depend on the shielding gas composition. To explain the phenomena inherent to a higher fusion rate at CC-, it is claimed that the fact of the arc to climb the wire surface at this polarity is the governing factor.
Welding; MIG; metal transfer; negative polarity
