Optimisation of GMAW via the alternating shielding gas technique

Student thesis: Doctoral Thesis


The use of the alternating shielding gas technique in arc welding systems has been previously studied due to advantages such as greater penetration of the weld joint, refined microstructure of the fusion zone, reduced heat input, and increased travel speeds of the welding torch. Yet, relatively little work has been carried out utilising this novel method. For instance, shielding gases employed during the arc welding procedures have been limited to Ar, CO and He, since the reactive behaviour of N within the arc plasma causes porosity development within the fusion zone. The present thesis extended the scientific knowledge regarding the alternating shielding gas technique via a systematic analysis utilising the gas metal arc welding process. It explored reductions in the shielding gas flow rate via variations in the frequency of alternation between the protective gases, investigated additions of N as a protective gas to weld DH36 grade steel plates, and examined ways to optimise the welding parameters. Measurements of the distortion of the workpiece, temperature of the weld, heat-affected zone (HAZ) and weld shape demonstrated the impact of the alternating shielding gas technique in reducing the heat input to the weldment. Microstructural characterisation coupled with analyses of the mechanical properties of the joint exhibited improved strength due to the faster welding procedures and greater formation of acicular ferrite. Additionally, mathematical modelling coupled with the genetic algorithm heuristic assisted with enhancing the efficiency of welds under the supply of N as a protective gas. The study carried out was able to diminish the shielding gas consumption even further by employing the alternating shielding gas technique. It also offered new insights in terms of shielding gas options, where the replacement of CO for N lowered the welding fume progression, eliminated the porosity development within welds, and generated a more uniform weld shape.
Date of Award7 Jun 2019
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SupervisorAlexander Galloway (Supervisor) & Athanasios Toumpis (Supervisor)

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