LASER NET SHAPE WELDING OF STEELS

Laser technologies have made distinguished contributions to modern industry. These have typically been realised through the important role played by lasers in the advancement of manufacturing technology in many areas such as welding, which has become an important joining technique and thus promoted the use of lasers in a wide variety of applications in the oil, gas, aerospace, aircraft, automotive, electronics and medical industries.A detailed review of previous work in the use of lasers for advanced manufacturing, and in particular, laser beam welding is given. The work reported in this thesis aims to develop a new method of laser welding. This is connected with investigations relating to the production of net shape welds for bead-on-plate welding and butt welding of mild steel plates. Based on the nature of its operation, use of a fibre laser was considered most suitable compared to other solid state lasers. Net-shape welds were demonstrated on mild steel plates using an IPG 1 kW single mode fibre laser with a maximum power output of 1000 W.The thesis shows results from experimental and modelling (based on finite element and computational fluid dynamic modelling) to validate the idea and the understanding of underlying scientific principles. The thesis is presented in the form of a collection of published work generated by the author during the course of this project. In addition, some results that are not yet published are also included. Design of experiments and statistical modelling has been used in the experimental work to understand the process parameter interactions. Microstructural and mechanical testing have been carried out to evaluate the performance of the welds. Net shaped (the weld bead is flat to the parent material surface) welds have been achieved and compared with standard welds. The understanding of net-shape weld formation and the effect of the laser welding parameters was enhanced by the theoretical modelling. The thesis concludes with a summary of scientific findings and an overview of future work.