Challenges in Application of Pulse Current Gas Metal Arc Welding Process for Preparation of Weld Joint with Superior Quality B. P. Agrawal School of Mechanical Engineering Galgotias University, G B Nagar Greater Noida, UP, India Rajeev Kumar IIMT College of Engineering Greater Noida, UP Abstract— Quality of weld joint in the form of its mechanical and metallurgical properties produced using gas metal arc welding process is governed by combination of parameters employed. These parameters also affect arc stability, bead appearance and thermal and metal transfer behaviour. For a given shielding gas, diameter and composition of filler wire, different modes of metal transfer that can be achieved are short circuit, globular, spray and pulsed spray. The spray metal transfer provides better ease of operation due to controlled mode of it but at relatively higher welding current above transition level. This may give rise to increase in heat input and temperature of weld pool along with wider weld isotherm which may adversely affect quality weld joint. This problem to some extent can be minimized by pulsing of welding current resulting in application of comparatively lower heat input and temperature of weld pool. But application of pulse current gas metal arc welding involves additional pulse parameters of pulse current Ip, base current, Ib, pulse on time, tp and pulse off time tb simultaneously interacting in nature. Together, there can be infinite combination of possible parameters at a given heat input. Therefore, the major challenges in application of pulse current gas metal arc welding process are to select an appropriate combination of pulse parameters that will be able to produce a weld joint with superior quality. Considering all these, detail study of methods of selection of pulse parameters in pulsed current gas metal arc welding has been discussed. Keywords — Pulse current; Pulse current duration; Base current; Base current duration; Pulse frequency. I. INTRODUCTION The increasing population of the world is demanding higher use of structures such as ships, offshore structures, steel bridges, and pressure vessels [1]. Fusion welding is the most widely used manufacturing process employed in fabrication of these structures. Because of requirement by the customers of high quality involving joining and competition from global market, the selection of joining process has become critical. This aspect forces the organization to go towards the automation of the process involved in fabrication. There are several choices of the fusion welding processes, such as common conventional shielded metal arc welding, gas tungsten arc welding, submerged arc welding and gas metal arc welding [2, 14]. These welding processes influence severity of weld thermal cycle in different manner depending upon amount of weld deposition, welding parameters and shielding environment. However, SMAW suffers the drawback of requirement of lower angle of attack by a skilled welder especially in case of relatively higher thickness with narrow gap and the process automation is comparatively critical. SMAW has also limitation of slag entrapment [3]. In case of GTAW process, the welding speed is considerably lower necessitating use of higher time in preparation of the weld joint. The submerged arc welding process can be successfully used for thick section welding but it requires rather higher heat inputs which may adversely affect the mechanical and metallurgical properties of the weld joint. These limitations can be overcome by application of GMAW process due to its ability to produce fast and continuous weld at any position even with lower heat input than submerged arc welding process. In GMAW process a continuous consumable solid wire electrode is used along with an externally supplied inert shielding gas. The consumable wire electrode produces an arc with the work pieces to be joined, made as a part of the electric circuit and also provides filler metal to the weld joint. The externally supplied shielding gas plays double role in GMAW, first it protects the arc and the molten or hot, cooling weld metal from the atmospheric air. Second, it provides desired arc characteristics through its effect on ionization. A distinct advantage of GMAW is the mode of molten metal transfer. There are four possible modes in which the molten metal in the form of droplets can be transferred from electrode to the work pieces. These are short circuiting, globular, spray and pulse spray type metal transfer. In GMAW process, characteristics of metal transfer, wire melting rate and size of the weld pool primarily dictates the weld thermal cycle and bead geometry, depending upon various welding parameters. Out of several modes of metal transfer of GMAW process, the spray mode of metal transfer offers better ease of operation primarily due to dominating electromagnetic force resulting in projected transfer of the droplet. In GMAW process utilizing continuous current, depending upon filler wire material, filler wire size and shielding environment, spray transfer can be achieved only at significantly higher welding current above transition level, which increases heat input to the weld [4, 47]. This, increase in heat input consequently enhances temperature of the weld pool and adversely affects quality of the weld joint in the form of its mechanical and metallurgical properties through its influence on weld thermal cycle, weld isotherm and geometry of the weld bead. The adverse conditions generated in weld by using higher heat input in International Journal of Engineering Research & Technology (IJERT) ISSN: 2278-0181 IJERTV5IS010350 Vol. 5 Issue 01, January-2016 http://www.ijert.org Published by : 319 (This work is licensed under a Creative Commons Attribution 4.0 International License.)