Efeito dos parâmetros de pulsação no processo TIG sobre a formação da poça de fusão

Abstract

The pulsed TIG process, despite being known for years, has no its applicative characteristics adopted to a desired level among welding users. One reason might be a lack of understanding of physical phenomena intrinsic to the process. This work objective was to study the influence of the pulse parameters on the weld pool formation and on the resulting geometry of the weld when using the pulsed TIG process. Bead-on-plate welds on carbon steel plates were carried-out, varying the pulse frequency and the amplitudes of the pulse current and of the background current, holding the same mean current value. The results obtained with and without cold wire feeding were compared. An analysis of the effect of pulse frequency and of the current difference between pulse and background levels has been done, taking into account how the latter factor exhibits itself through welding current RMS. Some effects of the pulsation on the bead-on-plate resulting geometrical parameters were observed, as well as on the defect formation, both superficial ("dragon's tail") and internal (elongated cavities or "tunnel porosity"), as a function of the weld pool formation phenomenon. There was an endeavour undertaken to study in more details the crater row formation, differentiating this phenomenon from that of another defect known as humping. It was determined that the main parameter, which governs the bead-on-plate geometry formation, particularly concerning the melted area, is the effective current (thermal effect) rather than the pulse parameters per se. On the other hand, the pulse parameters, in combination with the welding speed, have an effect on the formation of such defects as craters and cavities (arc mechanical effect). Moreover, it was confirmed that the feed speed and the wire diameter must be regulated in accordance with the pulse parameters to avoid a risk of appearing of the defect named as "dragon s tail."