Improvement to the surface finish of additive laser manufactured parts made by selective laser melting

Date

2014

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De Montfort University

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Thesis or dissertation

Peer reviewed

Abstract

The Selective Laser Melting (SLM) process has been used since the end of last decade for different applications in the industrial sector. The priority of the technique is to produce fully dense and functional metallic parts of very complex design, but it is limited by a few issues such as quality of surface finish and porosity. The current study focuses on improving the surface finish of parts built on an SLM machine through two different approaches of post processing technique, laser re-melting followed by electropolishing. In this investigation Renishaw’s SLM 125 was employed to produce 3Dimensional (3D) parts by using stainless steel 316L material with powder particle size ranges from 15 to 45 microns. Samples with different inclinations were constructed in order to generate samples with different surface roughness; the parts were measured and inspected for surface finish by measuring Ra. The initial surface roughness ranges from 10 to 20μm Ra. Due to the poor surface quality, laser re-melting was implemented as a first stage in order to eliminate the initial surface roughness. Laser re-melting as a post-processing technique was employed for re-melting procedure employing the RECLAIM machine at Manufacturing Technology Centre (MTC) Coventry. Different setups of process were analysed to optimize the parameters for re-melting. The results proved that the best results are conducted with laser energy density ranges between 2160 to 2700 J/cm2 to give exceptional results of surface roughness of about 1.4 μm±15% Ra. In such case it’s possible to say that laser re-melting has the capacity to improve surface finish by about 80% compared to the initial surface roughness created by SLM. In the second stage, improvement was carried out by implementing green process to reduce the waste, pollution and high toxicity using a suitable room temperature ionic liquid (RTLs) as a solution in order to eliminate the secondary surface roughness that comes after re-melting. Physical properties such as shininess and reflectivity were significantly improved, due to the capacity of the process to improve the surface roughness and remove the oxide film created during re-melting. The method proved that the best results were obtained when the specimens were anodically kept at current densities associated with potential ranges between (4 to 5.5 volt), maintained at (40 C°) to give roughness (Ra) less than 0, 5μm. These levels of voltage can be facilitated to operate and avoid any passivation of material dissolving, which can lead to pitting of the surface.

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