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Open AccessArticle

Phase Change with Density Variation and Cylindrical Symmetry: Application to Selective Laser Melting

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Department of Mechanical Engineering, Frederick University, Nicosia 1303, Cyprus
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Department of Physical Metallurgy and Materials Testing, Montanuniversität Leoben, Leoben 8700, Austria
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Department of Mechanical and Manufacturing Engineering, University of Cyprus, Nicosia 1678, Cyprus
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School of Materials, University of Manchester, ICAM-Pariser Building, Manchester M13BB, UK
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Office of the Provost, Nazarbayev University, Astana 010000, Kazakhstan
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College of Engineering and Computer Science, Vin University, Hanoi, Vietnam
*
Author to whom correspondence should be addressed.
Author deceased.
J. Manuf. Mater. Process. 2019, 3(3), 62; https://doi.org/10.3390/jmmp3030062
Received: 17 June 2019 / Revised: 10 July 2019 / Accepted: 22 July 2019 / Published: 25 July 2019
(This article belongs to the Special Issue Selective Laser Melting: Materials and Applications)
In this paper we introduce an analytical approach for predicting the melting radius during powder melting in selective laser melting (SLM) with minimum computation duration. The purpose of this work is to evaluate the suggested analytical expression in determining the melt pool geometry for SLM processes, by considering heat transfer and phase change effects with density variation and cylindrical symmetry. This allows for rendering first findings of the melt pool numerical prediction during SLM using a quasi-real-time calculation, which will contribute significantly in the process design and control, especially when applying novel powders. We consider the heat transfer problem associated with a heat source of power Q ˙   ( W / m ) per unit length, activated along the span of a semi-infinite fusible material. As soon as the line heat source is activated, melting commences along the line of the heat source and propagates cylindrically outwards. The temperature field is also cylindrically symmetric. At small times (i.e., neglecting gravity and Marangoni effects), when the density of the solid material is less than that of the molten material (i.e., in the case of metallic powders), an annulus is created of which the outer interface separates the molten material from the solid. In this work we include the effect of convection on the melting process, which is shown to be relatively important. We also justify that the assumption of constant but different properties between the two material phases (liquid and solid) does not introduce significant errors in the calculations. A more important result; however, is that, if we assume constant energy input per unit length, there is an optimum power of the heat source that would result to a maximum amount of molten material when the heat source is deactivated. The model described above can be suitably applied in the case of selective laser melting (SLM) when one considers the heat energy transferred to the metallic powder bed during scanning. Using a characteristic time and length for the process, we can model the energy transfer by the laser as a heat source per unit length. The model was applied in a set of five experimental data, and it was demonstrated that it has the potential to quantitatively describe the SLM process. View Full-Text
Keywords: selective laser melting (SLM); analytical melt pool calculation; phase change; cylindrical symmetry; line heat source selective laser melting (SLM); analytical melt pool calculation; phase change; cylindrical symmetry; line heat source
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MDPI and ACS Style

Fyrillas, M.M.; Ioannou, Y.; Papadakis, L.; Rebholz, C.; Matthews, A.; Doumanidis, C.C. Phase Change with Density Variation and Cylindrical Symmetry: Application to Selective Laser Melting. J. Manuf. Mater. Process. 2019, 3, 62.

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