Experimental sensitivity analysis of welding parameters during transition from globular to spray metal transfer in gas metal arc welding

Abstract

Since the discovery of arc welding at the beginning ofthe century, metal transfer has been a topic ofresearch interest. Metal transfer can, in fact be related to weld quality, because it affects the arc stability. Furthermore, it determines the weld spatter, penetration, deposition rate and welding position. Gas Metal Arc Welding (also known as Metal Inert Gas- or MIG welding) is the most co=on method for arc welding steels and aluminurn alloys. Approximately 40% of the production welding in the country is accomplished by this process in which the thermal phenomena and melting ofthe solid electrode are coupled to the plasma arc and the weld pool. Thus the therrno- fluid behaviour of the electrode and detaching drops can have significant effects on the subsequent weld quality and production rate. The knowledge of how metal transfer affects this arc welding process is important for welding control and process automation, as well as in the development of improved welding consumables. Gas metal arc welding has a distinct feature, indicated by the results of Lesnewich [24], [23], that for most gases, there is a discrete metal droplet formation change between low and high current operations. Naturally the droplet size will have a significant influence on the properties ofthe welds. In globular transfer which occurs at low current, the welding electrode melts and produces large droplets (usually larger in diameter than the electrode wire diameter). This mode of transfer is associated with high spatter levels and thus undesirable in terms of welding economics. An increase in welding current will, for most welding! shielding gases, produce metal transfer with smaller droplets, which is termed spray transfer. This mode oftransfer is associated with high voltage and amperage settings, thus producing high deposition rates limited to the flaUhorizontal position.