The laser deposition of shaped metallic wire using holographic optical elements
thesisposted on 01.06.2016 by Nicholas J. Goffin
In order to distinguish essays and pre-prints from academic theses, we have a separate category. These are often much longer text based documents than a paper.
This work covers an investigation of the use of customised laser beam profiles to improve the characteristics of wire-based laser deposition, by using the modified beam to control the thermal cycle of the deposition process. Inherent disadvantages of wire fed deposition vs. powder have been previously identified; namely that it is highly sensitive to changes in processing parameters, a tendency to low surface quality and a high incidence of porosity and cracking. Two potential avenues are identified and explored for the purpose of improving these disadvantages: Laser beam shaping and wire cross-sectional modification. The investigation is presented in both theoretical modelling and physical experiments. Surface reflectivity calculations are predicted that relate the incidence angle profile across the wire width with it absorption profile. Further heat transfer simulations were used to compare the heat conduction within the wire for the various wire cross-sections and experimental beam profiles. From this, melting simulations are presented with a variety of wire shapes and beam profiles. A series of experimental studies are presented comparing the use of different beam profiles on a single wire geometry, and then a single type of beam profile on different wire geometries. These are analysed principally with optical microscopy, with selected samples also studied via EBSD analysis. These corroborated the simulation results, where the use of altered beam profiles was found to give improved results in regard to the ability to form a melt pool, reduced power requirements and improved dilution characteristics. Combining a shaped beam with shaped wire gave further improvements. Subsequent to this, experimental clad tracks are presented that show the ability to create multiple layers in different directions, as well as the ability to use shaped wire with a wire feeder. This work shows that through the ability to modify the laser beam and wire cross-sectional profiles together with each other, the deposition properties can be improved; with a reduction in required power, an improvement in clad track quality and a reduction in process sensitivity.
- Mechanical, Electrical and Manufacturing Engineering