This document is an Executive Summary of individual submissions of work that the author has submitted towards the degree of Engineering Doctorate. The work comprises three main themes, which can be demonstrated in a broader sense as contributing towards improved productivity in fusion welding: i) The use of active fluxes for Tungsten Inert Gas (TIG) welding. ii) An investigation into the reduction of porosity when Metal Active Gas (MAG) welding galvanneal coated steel sheet used in the automotive industry. iii) The use of high power Nd:YAG laser welding for the production of large diameter, long distance land pipelines. Active fluxes give improved productivity by increasing the penetration depth of the TIG welding process by the simple addition of a flux applied to the surface. Although the productivity benefits of the process had been proven through a joint TWIIindustry project, the mechanism by which the fluxes produced this improvement was not fully understood. The first theme investigated the mechanisms at work in providing increased penetration and concluded that the primary mechanism responsible for the action of the fluxes was not due to a change in the flow of the molten pool but, as others had suggested, due to arc constriction. This work contributed to a greater understanding of the welding process and, furthermore, a greater understanding of the potential opportunities and limitations of the process when designing new fluxes for other alloy systems. MAG welds in coated steel sheet used in the automotive industry are prone to porosity leading to high reject rates. The second phase of work reported here determined welding procedures capable of delivering low porosity welds developed through statistical experimental design. These procedures demonstrated how low porosity welds could be made using conventional MAG welding techniques on steels that had been galvanneal coated to provide corrosion resistance. The procedures developed could be easily implemented at high production rates in an industrial manufacturing environment to reduce defect levels, and thus costly repairs or high scrap rates. The third theme of the work demonstrated how Nd:YAG laser welding could potentially be used to replace conventional arc welding techniques for land lay of gas transmission pipelines. The application of a single laser fill pass, made at high production rates, could replace the use of multiple MAG welding stations greatly reducing the costs associated with pipeline fabrication. BP has claimed that half pipeline cost savings of up to $300 million dollars are achievable through the implementation of such a technique. The justification for the use of lasers in pipelines is discussed in terms of both technical and economic suitability. Preliminary experimental work showed that high power Nd:YAG laser welds could achieve productivity targets, although in order to reduce defects and achieve the necessary structural performance it would be necessary to combine laser welding with a MAG welding process.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:528146 |
| Date | January 2002 |
| Creators | Howse, D. S. |
| Publisher | University of Warwick |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://wrap.warwick.ac.uk/2149/ |
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