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Optimisation of selective laser melting for a high temperature Ni-superalloy

Luke N. Carter (School of Metallurgy and Materials, University of Birmingham, Birmingham, United Kingdom.)
Khamis Essa (School of Mechanical Engineering, University of Birmingham, Birmingham, United Kingdom.)
Moataz M Attallah (School of Metallurgy and Materials, University of Birmingham, Birmingham, United Kingdom.)

Rapid Prototyping Journal

ISSN: 1355-2546

Article publication date: 15 June 2015

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Abstract

Purpose

The purpose of this paper is to optimise the selective laser melting (SLM) process parameters for CMSX486 to produce a “void free” (fully consolidated) material, whilst reducing the cracking density to a minimum providing the best possible fabricated material for further post-processing. SLM of high temperature nickel base superalloys has had limited success due to the susceptibly of the material to solidification and reheat cracking.

Design/methodology/approach

Samples of CMSX486 were fabricated by SLM. Statistical design of experiments (DOE) using the response surface method was used to generate an experimental design and investigate the influence of the key process parameters (laser power, scan speed, scan spacing and island size). A stereological technique was used to quantify the internal defects within the material, providing two measured responses: cracking density and void per cent.

Findings

The analysis of variance (ANOVA) was used to determine the most significant process parameters and showed that laser power, scan speed and the interaction between the two are significant parameters when considering the cracking density. Laser power, scan speed, scan spacing and the interaction between power and speed, and speed and spacing were the significant factors when considering void per cent. The optimum setting of the process parameters that lead to minimum cracking density and void per cent was obtained. It was shown that the nominal energy density can be used to identify a threshold for the elimination of large voids; however, it does not correlate well to the formation of cracks within the material. To validate the statistical approach, samples were produced using the predicted optimum parameters in an attempt to validate the response surface model. The model showed good prediction of the void per cent; however, the cracking results showed a greater deviation from the predicted value.

Originality/value

This is the first ever study on SLM of CMSX486. The paper shows that provided that the process parameters are optimised, SLM has the potential to provide a low-cost route for the small batch production of high temperature aerospace components.

Keywords

Acknowledgements

The authors would like to acknowledge the support of our collaborators from MicroTurbo/Safran Group. LNC would like to acknowledge the financial support provided by the Engineering and Physical Sciences Research Council (EPSRC) for his PhD Scholarship.

Citation

Carter, L.N., Essa, K. and Attallah, M.M. (2015), "Optimisation of selective laser melting for a high temperature Ni-superalloy", Rapid Prototyping Journal, Vol. 21 No. 4, pp. 423-432. https://doi.org/10.1108/RPJ-06-2013-0063

Publisher

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Emerald Group Publishing Limited

Copyright © 2015, Emerald Group Publishing Limited