Year

2003

Degree Name

Doctor of Philosophy

Department

Faculty of Engineering

Abstract

Rapid prototyping (RP) is a large and rapidly growing industry with many different processes either under development or already available commercially. These processes offer fast and flexible production of objects from a wide range of materials. They vary from being able to produce only prototypes of products, through to being suitable for production of finished products ready for service. Rapid prototyping by robotic gas metal arc welding (GMAW) uses metal deposited by the GMAW process to build metal products with engineering properties suitable for service conditions. Wear replacement (WR) involves the repair of worn metal surfaces through the deposition of weld metal, and can also be performed using robotic GMAW. Since both rapid prototyping and wear replacement by robotic GMAW involve the building up of metal objects from metal deposited by the GMAW process, it is possible to combine research in this area. Rapid prototyping and wear replacement using the robotic GMAW process may however give rise to stability problems. Geometric and thermal instability can be an inherent feature of the process, resulting in relatively poor dimensional accuracy and surface quality. Various research directions have been taken in the past in order to address these problems, however the effects of weld path design on process stability have not yet been well researched. The objective of this thesis was to study what effects weld path design can have on the stability of rapid prototyping and wear replacement by GMAW, in order to test whether weld path design could be used to improve process stability and performance. The hypothesis adopted in this thesis was that improved geometric and thermal stability should be possible if the material and heat input are optimised by control of the weld path through weld path design. It was found that the stability of the rapid prototyping and wear replacement by GMAW process is very sensitive to weld path design and that optimised open-loop weld path design can be used to greatly improve process stability and performance. A number of different mechanisms were identified through which the weld path design impacts on the stability and performance of the process and corresponding recommendations for weld path design were presented. The suitability of various weld path designs for different types of applications was assessed and the most optimal weld path designs for an expected wide range of applications were identified. By using one of the most recommended path strategies, rapid prototyping and wear replacement by GMAW systems can enjoy improved geometric and thermal stability and fewer problems with weld defects, through the choice of weld path. It was predicted that the most successful commercial rapid prototyping and wear replacement by robotic GMAW systems would utilise a flexible and multi-faceted approach, using a combination of technologies, in order to best address the various needs of the process as required for key areas of industrial application.

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Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.