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Application of in situ process monitoring to optimise laser parameters during laser powder bed fusion printing of Ti-6Al-4V parts with overhang structures

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Abstract

Enhanced levels of alloy print defects such as porosity are associated with the printing of overhang structures by laser powder bed fusion (L-PBF). This study compared the microstructure and porosity of Ti-6Al-4V overhang structures, with that observed for the bulk alloy. It was observed in the region around the overhang structure that the microstructure exhibited larger grain sizes and was less homogenous, compared to the that obtained within the bulk alloy. An increased level of porosity of up to 0.08% was also observed in the overhang print alloy, compared with the corresponding < 0.02% in the alloy bulk. It is hypothesised that these microstructural changes are associated with the excess heat generated in the overhang region, due to the decreased thermal conductivity of the powder immediately below the print layers, compared with solid alloy. During L-PBF alloy printing, in situ process monitoring of the melt pool emissions was obtained in the near-infrared range and correlated with the properties of the printed parts. This in-process data was used to assist in selecting optimal laser processing conditions, in order to help prevent melt pool overheating at the overhang. By systematically controlling the laser energy during the printing of the first fifteen layers over the overhang structure, the level of porosity was reduced, to the < 0.02% level of the bulk alloy. There was also an associated reduction in the roughness (Ra) of the overhang itself, with its Ra decreasing from 62.4 ± 7.3 to 7.5 ± 1.9 µm.

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Funding

This publication was produced from research supported in part by a research grant from Science Foundation Ireland (SFI) under Grant Number 16/RC/3872 and the SMART Eureka project APEM-AM. For the purpose of Open Access; the author has applied a CC by public copyright licence to any Author Accepted Manuscript version arising from this submission. The authors would also like to acknowledge the support provided by the Stryker European Operations Limited.

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Authors and Affiliations

  1. I-Form Centre, School of Mechanical and Materials Engineering, UCD, Dublin, D04 V1W8, Belfield, Ireland

    John J. Power, Owen Humphreys, Darragh Egan & Denis P. Dowling

  2. Irish Manufacturing Research, Block A, Collegeland, Rathcoole, Co. Dublin, D24 WC04, Ireland

    Mark Hartnett

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JP: conceptualisation, writing—review and editing, writing—original draught, methodology, visualisation, and investigation. OH: conceptualisation, writing—review and editing, methodology, visualisation, and investigation. MH: conceptualisation, methodology, and resources. DE: conceptualisation and methodology. DP.D: conceptualisation, project administration, resources, and writing—review and editing.

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Correspondence to John J. Power.

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Power, J.J., Humphreys, O., Hartnett, M. et al. Application of in situ process monitoring to optimise laser parameters during laser powder bed fusion printing of Ti-6Al-4V parts with overhang structures. Int J Adv Manuf Technol 130, 2297–2311 (2024). https://doi.org/10.1007/s00170-023-12794-z

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