Influence of Powder Deposition on Powder Bed and Specimen Properties

Abstract

Three-dimensional printing used to be a rapid prototyping process, but nowadays it is establishing as an additive manufacturing (AM) process. One of these AM techniques is selective laser sintering (SLS), which most often involves partial melting of the particles and therefore belongs to the category of powder bed fusion processes. Much progress has been made in this field by research on process parameters like laser power, hatch distance, and scanning speed while still lacking a fundamental understanding of the powder deposition and its influence on parts. A critical issue for economic manufacturing is the building time of parts with good mechanical properties, which can be reduced by lower surface roughness due to less or missing post processing. Therefore, the influence of three blade shapes on powder bed surface roughness has been evaluated for PA12 powder with three different grain size distributions by using advanced X-ray micro computed tomography (XMT) and a confocal laser scanning microscope (LSM). Along with those methods, new techniques for powder characterization were tested and compared. Lowest roughness has been achieved with a flat blade, based on a higher compression due to a larger contact zone between blade and powder bed. Furthermore, an anisotropic effect of the mechanical properties resulting from different building directions has been detected which can be explained by varying amounts of solid contact paths through the powder bed depending on powder application direction. In addition, an optimal combination of process parameters with an even compression of the powder bed leads to low surface roughness, complementing the advantages of additive manufacturing.

Nanoparticle Additivation Effects on Laser Powder Bed Fusion of Metals and Polymers—A Theoretical Concept for an Inter-Laboratory Study Design All Along the Process Chain, Including Research Data Management

“…PBF-LB is a layer-by-layer powder processing technique, and in each layer, the recoater spreads powder feedstocks on the building platform. During spreading, powder feedstocks must have excellent flowability to increase powder bed density and facilitate recoating a homogeneous and defect-free powder layer [74]. Since there is no international standard to measure PBF-LB powder feedstocks' flowability, a combination of several techniques such as density measurement (Hausner ratio, HR), ring shear test, and the rotating drum has to be used to measure the unmodified and additivated powder feedstocks' flowability.…”

Material Anisotropy in Additively Manufactured Polymers and Polymer Composites: A Review

“…Although the materials manufactured by FDM showed the most anisotropic levels, few researchers reported some noticeable levels of mechanical anisotropy in parts printed by SLS [ 13 , 18 , 19 , 20 ]. For instance, Ajoku et al reported the use of polyamide 12 (PA12) in producing parts with selected laser sintering (SLS).…”

“…Their samples showed a discrepancy of 16 per cent in tensile strength and 11.2 per cent in modulus for parts printed in the X, Y, and Z axes leading to unequal and lower mechanical properties in parts printed in Z build orientation than X orientation [ 18 ]. Beitz et al also reported a 48.6 per cent difference when build orientation was altered [ 19 ]. On the other hand, some other researchers reported no significant changes in the tensile strength of the parts printed by SLS [ 21 ].…”

“…On the other hand, some other researchers reported no significant changes in the tensile strength of the parts printed by SLS [ 21 ]. Parameters such as laser power (density), layer thickness, laser beam speed, build and powder deposition orientations as well as layer thickness, refresh rate, bed temperature and hatch pattern were reported to be amongst the influential processing parameters on the properties of the printed parts by SLS method [ 13 , 14 , 17 , 18 , 19 , 22 ].…”

Powder bed selective laser process (sintering/melting) applied to tailored calcium phosphate-based powders

“…It is known that the spreading and compression of the powder have an important effect on the properties of the printed parts. Beitz et al [47] offered an interesting summary of the results obtained by different authors on the spreading and compression of powder beds with different devices. They concluded, through the study of the spreading of nylon PA12 powders, that an even compression of the powder bed is better achieved when using both, a scraper or blade and a counter-rotating roller.…”