Suppression of powder spattering and melt pool instability in laser powder bed fusion via in-situ microwave volumetric scaffolding

Abstract Laser-based powder bed fusion (PBF-LB) is limited by powder spattering and melt pool instability caused by direct laser irradiation of loose powder beds, leading to defects, material loss, and poor surface quality. This study introduces a hybrid microwave (MW)-laser strategy that decouples bed stabilisation from precision melting by transforming loose powder into a coherent scaffold prior to laser exposure. Using copper as a model material, loose multimodal powder beds (0–3, 10–40, 45–105 µm) are volumetrically pre-sintered in seconds (< 80 s) using a 2.45 GHz MW source, without compaction or external susceptors. We demonstrate that fine particles (< 3 µm), acting as intrinsic MW couplers via skin-depth effects, enable rapid heating and create a mechanically robust, porous network that bridges larger particles. This scaffold alters the laser-powder interaction: high-speed imaging confirms the complete elimination of powder spattering and a transition to stable melt pool dynamics during subsequent laser melting. While full densification for structural applications requires further optimisation, the pre-sintered scaffold facilitates a density increase from 69.2 to 79.4%, serving as direct evidence of effective bed stabilisation and melt pool confinement (no claim for near-full densification—which typically exceeds 99.5% in conventional AM—but as evidence that the pre-MW sintered scaffold remains effectively laser-processable). This work establishes MW volumetric scaffolding as a novel, rapid pre-processing step to suppress instability in powder-bed fusion, offering a direct pathway to higher-stability in the AM process.