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Microwave processing in additive manufacturing

Hefford, Samuel John 2019. Microwave processing in additive manufacturing. PhD Thesis, Cardiff University.
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In this thesis the applications of microwave processing and measurement techniques for additive manufacture of metals by powder bed fusion (PBF) are investigated. This thesis presents an experimental setup developed for microwave heating and sintering of powder compacts using a cavity applicator. The setup uses directionally coupled power meters to achieve the functionality of a scalar network analyser, which allows the tracking of the resonant frequency during heating. Software is developed, which can be used to control the system and set the sample temperature using sensor measurements as feedback. Additionally, a cavity applicator is designed using a novel method for breaking frequency degeneracy of the excitation mode, TE011. This thesis shows that microwave sintering acts to reduce the microwave magnetic absorption of metal powder compacts. This is confirmed through experiment where various metal powders are sintered using microwave magnetic field. Measurements of the Q0 during the process are used to monitor the change in microwave loss of the powder compacts. This is important as previous results focus mainly on the postsintering properties, while there is very little data pertaining to in-process changes. This thesis presents a technique for measuring the surface resistance using a dielectric resonator. The novelty of the technique lays in its ability to determine the system losses by calibration in situ. This is achieved using a lift-off design, where the dielectric can be moved vertically within the resonator. Theoretical accuracy of this technique is shown to be good and simulation is used to investigate the effect on accuracy of different measurement conditions. Two prototype designs are produced and measurement results are presented for PBF manufactured metal parts, as well as metallised plastic surfaces produced by selective laser sintering (SLS) and stereo lithography (SLA).

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Engineering
Uncontrolled Keywords: Microwave; Additive; Heating; Sintering; Dietectric; Resonator.
Date of First Compliant Deposit: 27 March 2019
Last Modified: 27 Mar 2019 10:44

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