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Title: Laser processing of powder form titanium for rapid manufacture of 3D parts
Author: Littlewood, Gareth
ISNI:       0000 0004 2677 1268
Awarding Body: The University of Manchester
Current Institution: University of Manchester
Date of Award: 2009
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Rapid manufacture refers to those processes in which a component can be manufactured without the need for specific tooling. This reduces the time between the design stage and production of finished parts compared with traditional methods such as forging or casting. There are a number of laser based rapid manufacture processes currently available such as selective laser sintering and direct laser deposition which are both based on adding powder form material to a substrate in a layer-by-Iayer fashion. Subtractive methods such as laser milling have been developed to a lesser extent but are lirriited by low removal rates and problems caused by heat affected zones. Here, three new subtractive methods of laser rapid manufacture of near net shape titanium components were developed. Each was investigated and the most promising was chosen for further research. The chosen method is based on water assisted laser processing of partially sintered titanium powder. A block is made by partial sintering of titanium powder in a furnace such that it has the properties of being strong enough to be handled but still porous, with the powder particles retaining their spherical shape. The block is then soaked in liquid so that the interconnected pores become filled. A laser is used to irradiate the surface of the block which causes material removal from the irradiation site in a predictable way. The process was characterised by investigating the influence of process parameters: sintering temperature, laser energy density, powder particle size, laser repetition rate and type of liquid used to soak the blocks. The process was also analysed using high- . speed photography, emission spectroscopy and the probe-beam extinction technique to gain an understanding of the material removal mechanism. A computational model of the process was proposed based on the Smoothed Particle Hydrodynamics method. It was found that the mechanism of material removal is based on the explosive boiling of the liquid in the pores of the partially sintered block caused by heating from the laser. The rapid expansion of the exploding water creates a pressure which breaks the weak bonds between particles and ejects them from the surface. The new method can be faster than the current additive laser based rapid manufacture techniques and uses lower laser powers than the current laser milling processes. This is achieved through the choice of experimental conditions and laser parameters.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Eng.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available