Citation: MARIMUTHU, S. et al., 2015 AbstractThe shape complexities of aerospace components are continuously increasing, which encourages industries to refine their manufacturing processes. Among such processes, the selective laser melting (SLM) process is becoming an economical and energy efficient alternative to conventional manufacturing processes. However, dependent on the component shape, the high surface roughness observed with SLM parts can affect the surface integrity and geometric tolerances of the manufactured components. To account for this, laser polishing of SLM components is emerging as a viable process to achieve high-quality surfaces. This report details an investigation carried out to understand the basic fundamentals of continuous wave laser polishing of SLM samples. A numerical model, based on a computational fluid dynamic formulation, was used to assist the understanding of melt pool dynamics, which significantly controls the final surface roughness. The investigation identified the input thermal energy as the key parameter that significantly affect the melt pool convection, and essentially controls the surface quality. Minimum meltpool velocity is essential to achieve wider laser polished track width with good surface finish. Experimental results showed a reduction of surface roughness from 10.2μm to 2.4μm after laser polishing with optimised parameters. Strategies to control the surface topology during laser polishing of SLM components are discussed.

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Selective laser sintering (SLS) is an additive manufacturing process used to realise fully functional component manufacture. Numerous parameters are used in the process to control variables such as laser power, scan speed, laser spot size and overlap of scan vectors. All of these parameters can dramatically alter the sintering process and therefore final component properties. This paper presents how Raman spectroscopy intensity effects, caused by the surface roughness of the components produced, can be used to monitor the degree of sintering between particles in the SLS process.

The dehydration kinetics of theophylline monohydrate is a two-stage process. The first stage involves loosening of the crystal water followed by a second stage in which the water evaporates from the sample. During differential scanning calorimetry (DSC) measurements, the kinetics of the two stages can be dramatically altered because of the sample environment and DSC pan type. In-depth understanding of how the sample environment alters the dehydration process and the kinetics involved requires more than DSC experiments alone. This paper describes the use of a novel, simultaneous thermal and spectral technique to monitor the dehydration kinetics of theophylline monohydrate. The analysis of the results obtained on the combined DSC-near-infrared and DSC-Raman equipment clearly detects the two stages of the dehydration process and the polymorphic structural changes that take place. The combined technique provides a powerful method to monitor the dehydration of hydrous systems.

Near infrared spectroscopy has been used to monitor the effects of changing build parameters on the sintering process of selective laser sintering components. The surface roughness of the parts produced has been studied whilst modifying laser scan speed and laser power build parameters. Near infrared spectroscopy is shown to be a powerful tool in detecting subtle variations in the coalescence of particles that form the surface topology of the component. Principal component analysis (PCA) performed on the diffuse reflectance spectra obtained from the surface of the components shows a strong correlation between near infrared (NIR) spectra and build parameters. Using the chemometric model produced from the PCA analysis it is possible to calculate build parameters for unknown components, making NIR a useful aid for quality control of additive manufacturing technologies.