Abstract:
This thesis presents a novel economic Welding Advisory System (eWAS) known as RANKWELD for supporting a welding-engineer in selecting a cost effective welding procedure. The technique uses the weighted ranking of each welding parameter's relative empirical influence on producing the lowest cost weld to plan cost effective welds by avoiding the iterative task of acquiring exhaustive quantities of cost data that limit existing systems. Such well-founded decision-making helps fabricators to improve productivity by minimising the cost of welding in a simple, flexible and timely fashion. Never before has such a model been presented that gives as much emphasis to the cost of welding as to the technical development of a WPS. New heuristic tools are presented to generalise the cost data to unobserved scenarios. The heuristic tools rank welding parameters with respect to their impact on cost, use longer chains of reasoning to allow for the complex interaction of welding parameters, and "fill in" the unavailable cost data by means of generalising available cost data. In the absence of any existing tools within eWAS, the new tools have been compiled from domains as disparate as medical diagnostics, software engineering, statistical surveying and expert systems. An existing eWAS model called Information Systems with Cost Analysis (ISCA) has been extended to include rankings. Because ISCA cannot easily be extended to uncertain data, a nearest neighbour imputation is used to fill in incomplete cost data. To demonstrate that the new heuristic tools are indeed valid, extensive simulation case studies have been carried out using realistic Welding Procedure Specifications (WPS) and cost data. Case study results are presented that show the consistent improvement of the new Ranking Information System with Cost Analysis (RISCA) over existing ISCA models for a number of typical welded fabrications. The prototype implementation (RANKWELD) demonstrates that it is indeed feasible to develop an eWAS that will improve the productivity of fabricators by more fully informing them of the economic implications of seemingly minor technical welding decisions.
