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Title: Direct Laser Deposition of Quasi-Hollow Metallic Components
Author: Davis, Stephen James
ISNI:       0000 0001 3417 9289
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2007
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The work in this thesis is concerned with the deposition of quasi-hollow components fabricated using the additive manufacturing technique Direct Laser Deposition (DLD). Solid metallic layers are deposited onto the surface of a substrate via the introduction of metallic powder material into a melt pool created by the intensity of a laser beam. Successive deposition of tracks in a layer by layer fashion leads to the ability to build functional components. Presented in this thesis is an analytical approach to predicting the minimum power required to clad single tracks with minimal dilution into the substrate using an energy balance and conservation of mass equation. To help determine the minimum power required to deposit continuous, , well bonded clad tracks a simple geometric model was created that describes the change in cross-sectional area of a deposited clad track as its height and width increases. The results of this work produced curves which enabled the minimum power to be predicted for certain combinations of processing speed and powder mass flow rates. Abstract ii Abstract Stephen J. Davis The maximum overhang capable of being achieved using the 3-Axis DLD system described in this work was determined for different combinations of process parameters. Multiple clad tracks were deposited in layers to create solid, thin walls built at an incline to the vertical axis. The effects of the process parameters and clad track cross-sectional profile were investigated to examine the limits of the process when depositing un-supported overhang builds. It was found that a maximum overhang angle of _600 to the vertical could be deposited without the need of build supports. This greatly improves the flexibility of the process 10 terms of fabrication time and the complexity of the components capable of being built. Abstract Stephen J. Davis iii \Vith the ability to deposit non-vertical walls novel internal component geometries were deposited using the DLD process. Components with novel internal geometries, such as enclosed voids, are termed quasihollow components. The response of these components to axial compression and external pressure was investigated with the aid of finite element analysis and mechanical testing. It was found that components of equivalent mass having solid sections performed better at resisting the external loads compared to the quasi-hollow components. Upon collapse of the quasi-hollow components it was noticed that the orientation of the internal support structures influenced the location at which collapse occurred. Comparisons between the FE analysis and mechanical results ', showed that for a large quasi-hollow thin walled cylinder FE analysis underestimated the collapse load by 8.3%. For the case of the solid section thin wall cylinder the FE results underestimated the collapse load by 12.6%.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available