DROPLET DETACHMENT AND PLATE FUSION CHARACTERISTICS IN PULSED CURRENTGAS METAL ARC-WELDING

Molten metal droplet detachment and plate fusion characteristics, whic h have an important bearing on the weld quality, were influenced by th e parameters of pulsed current, viz. peak current (I-P), peak duration (T-P), background current (I-B) and background duration (T-B). The co mplex interdependence of the above parameters of pulsed current makes it difficult to select the most suitable combination of parameters for welding (Refs. 1-3). To resolve this problem, a first estimate of the pulse parametric zone based on burnoff, droplet detachment and are st ability criteria was obtained. It has been Further restricted taking i nto account the short circuit and burnback characteristics. Within thi s narrowed zone, the suitable combination of the pulsed current parame ters has been recommended on the basis of a combined criteria, viz. un iformity in are length, uniformity in droplet detachment and weld bead surface quality. This is done to obtain good quality welds. These stu dies have been carried out for a fixed pulse cycle time and one drople t detachment per pulse conditions. Further studies have been carried o ut for different types of droplet detachments, namely background detac hment, one droplet detachment per peak, two droplets detachment per pe ak and three droplets detachment per peak by varying pulse cycle time. The suitable type of droplet detachment has been selected on the basi s of uniformity in are length, uniformity in droplet detachment and un iformity in weld bead surface undulation. The effect of types of dropl et detachment on weld bead geometry has been studied. The peak energy, are noise level, reinforcement height and heat input were found to be low for background detachments. Also with background detachments, uni formity in are length and weld penetration were found to be high.