In situ monitoring of lunar regolith in PBF-LB: analyzing thermal history and densification mechanisms for improving part quality

Laser powder bed fusion (PBF-LB) of lunar regolith simulants is a key enabling technology for in situ resource utilization in extraterrestrial environments, yet process instability and high residual porosity currently limit the fabrication of functional components. This study presents the first multi-layer in situ monitoring investigation of regolith PBF-LB, combining high-resolution optical imaging for layer-wise surface assessment with infrared thermography for thermal history analysis. Experiments were conducted using two layer thicknesses (75 μm and 150 μm) under varying laser power and scanning speed conditions. The results reveal distinct process regimes governed by volumetric energy density and cumulative heat accumulation. Reduced layer thickness improved powder bed uniformity, while excessive energy input led to unstable melting, vitrification, and cracking. Intermediate energy conditions exhibited delayed instability driven by thermal history rather than instantaneous process parameters. A thermally informed inter-layer delay strategy was implemented as a proof of concept, demonstrating reduced porosity and improved process stability without increasing nominal energy input, and enabling the fabrication of a complex free-form demonstrator geometry. The findings demonstrate that thermal history is a primary driver of process stability in regolith PBF-LB and highlight the essential role of in situ monitoring for identifying stable processing regimes and mitigating heat-accumulation-driven defects. This work provides a realistic framework for robust process optimization of regolith-based PBF-LB for both terrestrial and extraterrestrial applications.