Powder particle movement during Powder Bed Fusion

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Powder Bed Fusion is a widely used technique to produce complex parts with different materials. In principle, a pre-placed powder layer is locally melted by a laser beam and thereby fused to the previous tracks and layers. This technique offers high flexibility at fast processing speeds. High-speed laser scanning enables, on the one hand, the fast processing but induces heat, forces and pressure in and around the processing zone on the other hand. The behavior of the single particles on the powder bed around the processing zone is hard to observe and therefore not sufficiently investigated. High-speed-imaging was used in this work to track the movement of the powder particles of the powder bed during Powder Bed Fusion in order to observe and explain their behaviour. It could be observed that powder particles move towards the melt pool affecting a large area around the melt pool, which changes the powder distribution of the powder bed. This indicates that a strong gas flow is constantly present during processing, which is thought to be due to the metal vapour induced by laser evaporation but can be also induced when no vapour is present due to the temperature and pressure increase around the processing zone.