Droplet Detachment and Plate Fusion Characteristics in Pulsed Current Gas Metal Arc Welding

摘要

Molten metal droplet detachment and plate fusion characteristics, which have an important bearing on the weld quality, were influenced by the parameters of pulsed current, viz. peak current (I_P), peak duration (T_P), background current (I_B) and background duration (T_B). The complex interdependence of the above parameters of pulsed current makes it difficult to select the most suitable combination pf parameters for welding (Refs. 1-4). To resolve this problem, a first estimate of the pulse parametric zone based on burnoff, droplet detachment and arc stability criteria was obtained. It has been further restricted taking into account the short circuit and burnback characteristics. Within this narrowed zone, the suitable combination of the pulsed current parameters has been recommended on the basis of a combined criteria, viz. uniformity in arc length, uniformity in droplet detachment and weld bead surface quality. This is done to obtain good quality welds. These studies have been carried out for a fixed pulse cycle time and one droplet detachment per pulse conditions. Further studies have been carried out for different types of droplet detachments, namely background detachment, one droplet detachment per peak, two droplets detachment per peak and three droplets detachment per peak by varying pulse cycle time. The suitable type of droplet detachment has been selected on the basis of uniformity in arc length, uniformity in droplet detachment and uniformity in weld bead surface undulation. The effect of types of droplet detachment on weld bead geometry has been studied. The peak energy, arc noise level, reinforcement height and heat input were found to be low for background detachments. Also with background detachments, uniformity in arc length and weld penetration were found to be high.