Fibre laser metal deposition with wire : parameters study and temperature control

This research addresses the development of a laser metal deposition process with wire feeding and melt pool temperature control. The system consists of a2 kW fibre laser, a CNC table, a wire feeder and a temperature monitoring and control system. A study of the influence of the main parameters on the process and on the deposited bead geometry was performed. The parameters analysed were: laser power, traverse speed and wire feed rate. As a result of this study, a process window was established for metal deposition of stainless steel 308LSi (wire) on stainless steel 304 (plate). The influence of the parameters on the bead geometry (height and width) was analysed applying the Design of Experiments methodology, using a full factorial design 3k. The results are presented, together with important practical considerations for laser metal deposition with wire. A closed-loop temperature control system was developed: it controls the melt pool temperature by means of modifying the laser power. The melt pool temperature was measured by a two-colour pyrometer, whereas a single-colour pyrometer was used for monitoring the workpiece (upper layer) temperature. A model of the melt pool was derived from a heat balance equation. It was then utilized for the design of the controller in the discrete domain, using the root locus method. The control algorithm was developed in LabVIEW software and executed in a computer. The control system was implemented successfully and was utilized to build single-bead walls and cylinders of stainless steel 308LSi. The study performed on the parameters and the developed temperature controller proved to be very effective tools to facilitate the transition to the deposition of titanium alloy Ti-6A1-4V, requiring only minimum adaptations. Single-bead walls and cylinders were also built in this material. Stable and smooth metal deposition was achieved for both materials. During the experiments, several strategies for the automation of wire metal deposition of multilayered structures were developed. Finally, mechanical tests were performed. The mechanical properties of the deposited materials are comparable to those in wrought (annealed) condition and to similar alloys made by laser powder deposition systems. The system developed in this work provides a means to perform stable and smooth wire metal deposition, achieving good mechanical properties. It also facilitates the transition to deposit different materials. It has a flexible structure and can be expanded or adapted to be used in other wire metal deposition systems.EThOS - Electronic Theses Online ServiceGBUnited Kingdo