Design driven defects in laser powder bed fusion: correlation between in-situmonitoring data and ex-situ measurement
Typ
Examensarbete för masterexamen
Master's Thesis
Master's Thesis
Program
Materials engineering (MPAEM), MSc
Publicerad
2023
Författare
Belsure, Nikhil Gautam
Sundar, Vishal
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
Industrial adoption of Laser Powder Bed Fusion (LPBF) is hindered by lack of process
reliability and stability and the resulting build part quality. Manufacturing
defect-free parts is crucial for quality-critical industries such as aerospace. Prior
research has proposed in-situ monitoring of LPBF as a novel tool for early defect
detection and improving process reliability. Numerous studies investigate causal
correlation between anomalies in in-situ monitoring and defects and establishing
ground-truth for the anomalies observed in in-situ monitoring data. However, the
detection and characterization of defects generated by challenging geometries is relatively
underexplored. This study aims to correlate anomalies observed in LPBF
in-situ monitoring systems to design-driven defects arising from challenging geometries.
Further, these defects are characterized through ex-situ measurements using
non-destructive evaluation (NDE), namely X-ray computed tomography (XCT), 3D
scanning, and optical surface roughness measurement. Geometries with challenging
design features such as thin structures and unsupported overhangs, were designed
and printed to provoke defects such as geometrical deviations, surface roughness,
and internal flaws. Monitoring data obtained from the LPBF platforms, including
optical tomography (OT) images, spectral data, and powder bed images, were analyzed
to identify indications of these defects. Distortions in thin geometries exhibited
strong correlations to protrusion of the part through the powder bed after powder
dosing. Hotspots that corresponded with short hatch vectors and downskin surfaces
of overhangs lesser than 45° indicated surface defects. It was observed that hotspots
did not always indicate the presence of defects. Sometimes hotspots appeared in
areas or parts that were exposed in the prior powder bed layer. Correlating the
shifting of thin geometries due to recoater influences with the monitoring data was
possible with long exposure OT. The findings highlight the importance of considering
geometry-induced defects in LPBF processes and provided a validation for the
anomalies observed in monitoring data.
Beskrivning
Ämne/nyckelord
additive manufacturing , laser powder bed fusion , in-situ monitoring , Non-Destructive Evaluation , X-ray CT , 3D scanning , surface roughness , geometrical deviation