Concepção e avaliação de uma técnica de pulsação da alimentação de arame baseada em um "pulmão ativo" para soldagem MIG/MAG

Abstract

The way that material is added in arc welding has been the subject of innovations in recent years. Despite the idea of pulsing the wire feed is not new, the efficacy of this technique has limited scientific support. Besides, mechanisms for wire pulsation are linked to internal feeders or special torches, which makes difficult, in most cases, its industrial acceptance. Thus, this work aims to apply and evaluate the wire feed pulsation in GMA welding based on the conception of an “active lung” (a national technology) that can be used with conventional feeders and torches and act in both the metallic transfer and weld bead formation. In the first phase of the work, an “active lung” approach was explored, evaluated, and implemented to develop an equipment to pulsate the wire feed in a controlled manner and that could be coupled with any conventional feeder. In the second phase, the pulsation promoted by this equipment was applied to act on the metallic transfer in the GMAW process, both in the electrode-wire and in cold-wire feeding. The potential of this technique to promote changes in the process performance under different modes of metallic transfer was explored through the variation of amplitude, frequency, and pulsation form. High-speed filming, current and voltage oscillograms, thermographic filming, and geometric aspects of the weld beads after macrographic exam were used for the analysis. The electrode-wire feed pulsation allows to control the frequency and, consequently, the volume by which the droplets are transferred to the weld pool by following two approaches: the first one by mechanical impulse and the second one by surface tension. In the first case, a simplified physical model included another force acting to detach the droplets, influencing the convective mass and the heat transfer behavior of the molten pool (Marangoni flow) and, therefore, the factors that govern the weld bead formation. In the second case, it was possible to weld with high voltage in short-circuit mode. When the feed pulsation was applied to the cold-wire, no sensitive influence was observed regarding the weld bead geometries, although it affected the behavior of the arc, the electrical signals, and the metallic transfer. Even so, the pulsed cold-wire interfered in the temperature profile outside the molten pool. For the highest pulsation frequency explored, regardless of the feed angle, less heat was transferred to the test plate. Further, lower heat input in this case limited grain growth, reducing the coarse grained heat affected zone HAZ and resulting in a refined microstructure. Hence, the wire feed pulsation was successfully demonstrated as being applicable to the GMAW process through the conception of an “active lung”.