Dry powder coating in additive manufacturing

Abstract

Dry powder coating is used in many industries to tailor the bulk solid characteristics of cohesive powders. Within this paper, the state of the art of dry coating of feedstock materials for powder based additive manufacturing (AM) processes will be reviewed. The focus is on feedstock materials for powder bed fusion AM processes, such as powder bed fusion of polymers with a laser beam and powder bed fusion of metals with lasers or an electron beam. Powders of several microns to several ten microns in size are used and the feedstock’s bulk solid properties, especially the flowability and packing density are of immanent importance in different process steps in particular for powder dosing and spreading of powder layers onto the building area. All these properties can be tuned by dry particle coating. Moreover, possibilities to improve AM processability and to manipulate the resulting microstructure (c.f. grain refinement, dispersion strengthening) by adhering nanoparticles on the powders will be discussed. The effect of dry coating on the obtained powder properties along the whole AM process chain and the resulting part properties is assessed. Moreover, appropriate characterization methods for bulk solid properties of dry-coated AM powders are critically discussed.

Expanding polymeric feedstocks for powder bed fusion via rational control of liquid–liquid phase separation

“…28 Several approaches have been attempted to increase flowability of P-PBF powders, where a common method involves the dry coating of the powder with nanoparticles, such as SiO 2 , carbon black, iron oxide and graphene. 29 Other than particle shape, particle size is also an essential factor in the suitability of a powder for P-PBF, where particles with 20-100 μm diameter perform well in P-PBF. 30,31 Larger particles do not flow easily and often require post-processing to create a smooth surface; while powders with smaller particles exhibited low flowability, inhibiting the spreading of new powder.…”

“…Powders formed from solution precipitation often form potato‐shaped particles that exhibit good flowability, while the irregular shaped particle created from cryogenic milling display the worst flowability 28 . Several approaches have been attempted to increase flowability of P‐PBF powders, where a common method involves the dry coating of the powder with nanoparticles, such as SiO 2 , carbon black, iron oxide and graphene 29 …”

A thick wall concept for robust treatment of contacts in DEM simulation of highly polydisperse particulate systems

“…If the small particles are sufficiently fine, they are subjected to adhesive forces and are often found attached to coarser particles, potentially detaching as a result of collisions with the containing walls or by the shearing action of a fluid stream. Examples include formation of dust during bulk solids handling (Schulz et al, 2022;Schulz et al, 2023), the deaggregation of active pharmaceutical ingredient (API) powder from coarser carrier particles in dry powder inhalation devices (Sharma and Setia, 2019;Chaurasiya and Zhao, 2020;Spahn et al, 2022), the production of active material with a layer of conducting material (e.g., carbon black) during dry mixing in battery electrodes manufacturing (Lischka et al, 2024), the use of solid flow-aids to improve powder flowability or to track powder mixing (Fulchini et al, 2017;Karde et al, 2023;Khala et al, 2023) and the improvement of powder bed homogeneity in additive manufacturing of ceramic materials by using bimodal particle size distribution (Sofia et al, 2018;Schmidt and Peukert, 2022).…”