Challenges in Application of Pulse Current Gas Metal Arc Welding Process for Preparation of Weld Joint with Superior Quality

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.

Laser Hybrid Butt Welding of Large Thickness Naval Steel

“…The evidence of LAHW application to weld large scale great thickness plates can be clearly seen in some cases like the study of Agrawal [48], where a joint with 25 m length was performed. Thus, it is indicated that for the execution of such joint with autogenous laser process (without the use of filler material) it would be required to maintain a maximum separation of 0.3 mm along the entire joining zone (25 m), being in this case almost unfeasible from a practical point of view.…”

“…The concise achievable penetration depends on the characteristics of the laser source used; LAHW usually allows welding relatively high plate thicknesses (in the order of 10 to 15 mm) [21]. Hybrid welding is proposed as ideal joining process for large-scale applications, such as those required in the building of chemical tankers, gas or oil tankers, since thickness of material to be welded is usually greater than 20 mm [48].…”

“…The improvement in the finishing the hull of ships has made it possible to reduce the need to carry out additional finishing processes, such as cutting works on-site to adjust the distortion generated by the welding. The excellent surface finish of LAHW process has allowed increasing also the productivity [48].…”

“…The production of large scale welding requires heavy equipment. Trumpf has recently opened a facility in Austria, where a hybrid laser welding head from Fronius International is able to join sheets of up to 20 tons in weight, generating welds with 8 mm thickness [48].…”

“…An example of this is the study carried out by Rethmeier [56], in which the base material selected was the typical pipeline steel API 5L X65. Frequently, in the HALW process, the laser is used to achieve the maximum penetration possible and the arc welding, for the incorporation of additional material that allows to cover the gaps and/or to modify the composition of the material in the welding zone [10,48]. In this sense, the contribution of a filling material is particularly advantageous for large scale applications.…”