Proceedings of the
9th International Conference of Asian Society for Precision Engineering and Nanotechnology (ASPEN2022)
15 – 18 November 2022, Singapore

Correlation of In-Process Monitoring Data and Defects in X-ray CT for Direct Metal Laser Sintering

Kin Keong Wong1,a, Zheng Jie Tan1, Yvonne Lim2 and Kenny Lee2

1Advanced Remanufacturing and Technology Centre (ARTC), 3 Cleantech Loop, #01/01 CleanTech Two, Singapore 637143

2EOS Singapore Pte Ltd, 2 Woodlands Sector 1 #05-09 Woodlands Spectrum 1, Singapore 738068


Direct Metal Laser Sintering (DMLS) is a type of Additive Manufacturing (AM) technique which is well suited for production of complex parts in low to medium volumes. The lack of quality assurance has been identified as a key barrier that reduces the speed of AM adoption by manufacturers for serial production. During AM serial production, random process instabilities can happen, and these can manifest to defects such as lack-of-fusion pores and cracks, which has a strong impact on fatigue performance and lead to early component failures.
In this study, an array of cutout coupons of an industrial swirler component was fabricated using the EOS M290 system. In-process monitoring using EOSTATE Exposure Optical Tomography (OT) was used to detect process instability during the production process. The Exposure OT is based on a camera collecting near-infrared emissions similar to that of a thermal imaging camera. Process instability was artificially generated by altering the inert gas flow at specific regions of the build platform. A poor inert gas flow condition can trigger smoke plume and splattering effect which can then lead to defocusing of the laser beam.
The process instability can be reflected as hotspots, which can be detected by the OT monitoring system. These hotspots can be correlated to porosity in X-ray CT scan. However, Exposure OT is sensitive and not all hotspots manifest into defects when compared to the CT results as some hotspots are unique process signature within the build part & support geometry. Comparative analysis of the data between OT and X-ray CT showed a series of conditions for which one can have strong correlation to defects. Firstly, hotspots with extreme mean grey values above a threshold of 80K have greater potential to manifest into porosities. Secondly, the overlap of hotspots in consecutive layers was observed to have greater potential to manifest into porosities. These conditions can be used to accelerate the decision-making process under a serial production scenario, where post inspection processes such as non-destructive and destructive testing can be reduced, lowering cost of quality assurance for parts.

Keywords: Additive Manufacturing, Direct metal laser sintering, In-process Monitoring, Quality assurance, X-ray CT, Serial production.

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