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Open accessJournal ArticleDOI: 10.3390/MET11030418

The Influence of Particle Shape, Powder Flowability, and Powder Layer Density on Part Density in Laser Powder Bed Fusion

04 Mar 2021-Vol. 11, Iss: 3, pp 418
Abstract: The particle shape influences the part properties in laser powder bed fusion, and powder flowability and powder layer density (PLD) are considered the link between the powder and part properties. Therefore, this study investigates the relationship between these properties and their influence on final part density for six 1.4404 (316L) powders and eight AlSi10Mg powders. The results show a correlation of the powder properties with a Pearson correlation coefficient (PCC) of −0.89 for the PLD and the Hausner ratio, a PCC of −0.67 for the Hausner ratio and circularity, and a PCC of 0.72 for circularity and PLD. Furthermore, the results show that beyond a threshold, improvement of circularity, PLD, or Hausner ratio have no positive influence on the final part density. While the water-atomized, least-spherical powder yielded parts with high porosity, no improvement of part density was achieved by feedstock with higher circularities than gas-atomized powder.

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Topics: Hausner ratio (72%)

5 results found

Open accessJournal ArticleDOI: 10.1108/RPJ-01-2021-0010
Abstract: Powder bed-based additive manufacturing (AM) is a promising family of technologies for industrial applications. The purpose of this study is to provide a new metrics based on the analysis of the compaction behavior for the evaluation of flowability of AM powders.,In this work, a novel qualification methodology based on a camera mounted onto a commercially available tap density meter allowed to assess the compaction behavior of a selection of AM materials, both polymers and metals. This methodology automatizes the reading of the powder height and obtains more information compared to ASTM B527. A novel property is introduced, the “tapping modulus,” which describes the packing speed of a powdered material and is related to a compression/vibration powder flow.,The compaction behavior was successfully correlated with the dynamic angle of repose for polymers, but interestingly not for metals, shedding more light to the different flow behavior of these materials.,Because of the chosen materials, the results may lack generalizability. For example, the application of this methodology outside of AM would be interesting.,This paper suggests a new methodology for assessing the flowing behavior of AM materials when subjected to compression. The device is inexpensive and easy to implement in a quality assurance environment, being thus interesting for industrial applications.

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Topics: Compaction (50%)

1 Citations

Journal ArticleDOI: 10.1016/J.POWTEC.2021.10.017
Lin Wang1, Zongyan Zhou1, Zongyan Zhou2, Erlei Li1  +2 moreInstitutions (2)
01 Jan 2022-Powder Technology
Abstract: Discrete element method is used in this work to examine the mechanisms determining powder deposition efficiency during powder spreading in powder bed fusion additive manufacturing. The results reveal that powder flow in the powder pile is critical for the formation and break of transient jamming. The forces on the underlying part increase first with spreading speed then decrease with a large fluctuation. For varied spreader shapes, a small inclined angle of the spreader surface makes the force barrier farther from the discharging gap, creating a larger region which ensure enough powder supply to the gap. Furthermore, a small inclined angle of the spreader surface close to the gap results in less particle motion conflicts at the gap and ensures larger discharging rate through the gap. This mechanism explains why spreaders with inclined or round surfaces help increase powder deposition efficiency.

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Open accessDOI: 10.1007/S40192-021-00240-5
11 Nov 2021-
Abstract: Research concerned with the identification as well as quantification of satellites found within metallic powders has recently demonstrated the promise of implementing Mask R-CNNs, instance segmentation, and transfer learning. Though the original research and development of such an approach demonstrated the functionality of the data-driven image analysis framework, questions remained in regards to the scale-ability of the Mask R-CNN-based model. Accordingly, the present work demonstrates the fact that the originally formulated model can be expanded to include scanning electron micrographs to various powder types at variate magnifications (rather than the original case of micrographs of a single powder type at a single magnification). Moreover, the present work establishes a process that enables users to specifically target which images will have most impact on increasing generalize-ability and performance in order to optimize maximum improvement of the model with the least amount of images annotated. Beyond this, we also outline a method of auto-labeling satellites in images by using a trained model to increase its own training set size.

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Open accessJournal ArticleDOI: 10.1016/J.ADDMA.2021.102489
Seungkyun Yim1, Huakang Bian1, Kenta Aoyagi1, Kenta Yamanaka1  +1 moreInstitutions (1)
Abstract: The quality of powder beds is a key factor governing the density of bulk parts produced by the powder bed fusion–additive manufacturing (PBF-AM) process. Conventional assessments of powder flowability cannot be used to evaluate spreadability of the spreading process owing to different dynamic conditions used. Therefore, factors that have dominant effects on the powder bed properties must be investigated. In this study, two types of Ti 48Al 2Cr 2 Nb powders, produced by the plasma rotating electrode process (PREP) and gas atomization (GA), were used to compare spreading behaviors and powder bed properties. The static and dynamic flowabilities of the PREP powder were better than those of the GA powder, while the packing density and surface roughness of the powder bed were worse. During the spreading process, the recorded recoating angle gradually increased for the GA powder, while it remained constant for the PREP powder. The increase in the recoating angle for the GA powder was due to the preferential segregation of fine particles during the spreading process. The discrete element method (DEM) model was calibrated by the fitting static and dynamic angle of repose. Based on the DEM model, three particle-flow regimes were identified: the vortex region, free flowing region, and shear stress region. In the shear stress region, the contact force between the GA powder particles was lower than that of the PREP powder, resulting in high packing density. Artificial manipulation of the particle size and shape in the DEM simulation revealed that the predominant factor governing the powder bed properties between the GA and PREP powders was the particle size distribution. We believe that our study provides an improved understanding of the powder-spreading mechanism and optimization of the powder bed properties.

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Topics: Angle of repose (53%), Discrete element method (51%), Particle-size distribution (50%) ... show more

Journal ArticleDOI: 10.1016/J.ADDMA.2021.102250
Ilaria Baesso1, David M. Karl2, Andrea Spitzer1, Aleksander Gurlo2  +2 moreInstitutions (2)
Abstract: The flow behavior of powders has an essential role in many industrial processes, including powder bed additive manufacturing. The characterization of the flow behavior is challenging, as different methods are available, and their suitability for an application in additive manufacturing is still controversial. In this study, six standardized methods (measurement of bulk density by ISO 60 and by ASTM B329, angle of repose by ISO 4324, discharge time by ISO 6186 and by ASTM B964–16, and Hausner Ratio by ASTM 7481–18), the rotating drum method (by GranuDrum) and powder rheometry (Anton Paar powder cell), were applied to five size fractions of a crushed quartz sand powder and compared. A statistical approach is proposed and discussed to correlate the obtained flowability indexes with the packing density of powder beds deposited layer-by-layer, and these correlations are compared between methods. Overall, the measurement of bulk density by ASTM B329 showed the best correlation with the powder bed density. Advanced methods such as the rotating drum method and powder rheometry did not demonstrate particularly good correlations, however they provided complementary information which can be useful to assess the dynamic behavior of powders.

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Topics: Hausner ratio (61%), Angle of repose (51%), Rheometry (50%)

36 results found

Open accessJournal ArticleDOI: 10.1080/09506608.2015.1116649
Abstract: Additive manufacturing (AM), widely known as 3D printing, is a method of manufacturing that forms parts from powder, wire or sheets in a process that proceeds layer by layer. Many techniques (using many different names) have been developed to accomplish this via melting or solid-state joining. In this review, these techniques for producing metal parts are explored, with a focus on the science of metal AM: processing defects, heat transfer, solidification, solid-state precipitation, mechanical properties and post-processing metallurgy. The various metal AM techniques are compared, with analysis of the strengths and limitations of each. Only a few alloys have been developed for commercial production, but recent efforts are presented as a path for the ongoing development of new materials for AM processes.

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Topics: Advanced manufacturing (50%), 3D printing (50%)

1,200 Citations

Journal ArticleDOI: 10.1016/J.MSEA.2006.04.117
Abdolreza Simchi1Institutions (1)
Abstract: In the present work, the densification and microstructural evolution during direct laser sintering of metal powders were studied. Various ferrous powders including Fe, Fe–C, Fe–Cu, Fe–C–Cu–P, 316L stainless steel, and M2 high-speed steel were used. The empirical sintering rate data was related to the energy input of the laser beam according to the first order kinetics equation to establish a simple sintering model. The equation calculates the densification of metal powders during direct laser sintering process as a function of operating parameters including laser power, scan rate, layer thickness and scan line spacing. It was found that when melting/solidification approach is the mechanism of sintering, the densification of metals powders ( D ) can be expressed as an exponential function of laser specific energy input ( ψ ) as ln(1 − D ) = − Kψ . The coefficient K is designated as “densification coefficient”; a material dependent parameter that varies with chemical composition, powder particle size, and oxygen content of the powder material. The mechanism of particle bonding and microstructural features of the laser sintered powders are addressed.

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Topics: Selective laser sintering (68%), Sintering (55%), Laser power scaling (54%) ... show more

478 Citations

Open accessJournal ArticleDOI: 10.1016/J.ACTAMAT.2015.06.004
Chunlei Qiu1, Chinnapat Panwisawas1, Mark Ward1, Hector Basoalto1  +2 moreInstitutions (1)
01 Sep 2015-Acta Materialia
Abstract: In this study, the development of surface structure and porosity of Ti–6Al–4V samples fabricated by selective laser melting under different laser scanning speeds and powder layer thicknesses has been studied and correlated with the melt flow behaviour through both experimental and modelling approaches. The as-fabricated samples were investigated using optical microscopy (OM) and scanning electron microscopy (SEM). The interaction between laser beam and powder particles was studied by both high speed imaging observation and computational fluid dynamics (CFD) calculation. It was found that at a high laser power and a fixed powder layer thickness (20 μm), the samples contain particularly low porosity when the laser scanning speeds are below 2700 mm/s. Further increase of scanning speed led to increase of porosity but not significantly. The porosity is even more sensitive to powder layer thickness with the use of thick powder layers (above 40 μm) leading to significant porosity. The increase of porosity with laser scanning speed and powder layer thickness is not inconsistent with the observed increase in surface roughness complicated by increasingly irregular-shaped laser scanned tracks and an increased number of discontinuity and cave-like pores on the top surfaces. The formation of pores and development of rough surfaces were found by both high speed imaging and modelling, to be strongly associated with unstable melt flow and splashing of molten material.

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Topics: Selective laser melting (57%), Porosity (57%), Laser power scaling (56%) ... show more

467 Citations

Open accessJournal ArticleDOI: 10.1016/J.ACTAMAT.2016.05.017
01 Aug 2016-Acta Materialia
Abstract: Understanding laser interaction with metal powder beds is critical in predicting optimum processing regimes in laser powder bed fusion additive manufacturing of metals. In this work, we study the denudation of metal powders that is observed near the laser scan path as a function of laser parameters and ambient gas pressure. We show that the observed depletion of metal powder particles in the zone immediately surrounding the solidified track is due to a competition between outward metal vapor flux directed away from the laser spot and entrainment of powder particles in a shear flow of gas driven by a metal vapor jet at the melt track. Between atmospheric pressure and ∼10 Torr of Ar gas, the denuded zone width increases with decreasing ambient gas pressure and is dominated by entrainment from inward gas flow. The denuded zone then decreases from 10 to 2.2 Torr reaching a minimum before increasing again from 2.2 to 0.5 Torr where metal vapor flux and expansion from the melt pool dominates. The dynamics of the denudation process were captured using high-speed imaging, revealing that the particle movement is a complex interplay among melt pool geometry, metal vapor flow, and ambient gas pressure. The experimental results are rationalized through finite element simulations of the melt track formation and resulting vapor flow patterns. The results presented here represent new insights to denudation and melt track formation that can be important for the prediction and minimization of void defects and surface roughness in additively manufactured metal components.

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420 Citations

Journal ArticleDOI: 10.1016/S0032-5910(98)00208-3
Ezzat Chan Abdullah1, Derek Geldart1Institutions (1)
03 Mar 1999-Powder Technology
Abstract: Two equipments for measuring the bulk density of powders have been used to assess the flowability of porous and non-porous powders in which particle size changes as a result of controlling the percentage of fine components in the mixtures. The Hosokawa Powder Tester, which measures the aerated and tapped bulk densities, gives accurate measurements of bulk density because a fixed volume of powder is used and the mass of the powder can be measured accurately. On the other hand, the Copley Tap Density Volumeter, which uses a fixed mass of powder, gives inaccurate measurements due to the difficulty of reading the volume from the graduated cylinder. Generally, the flowability of powder increases with the increase of particle size, and there appears to be a critical size range above which flowability does not show any improvement. The packing of particles in two conditions, i.e., aerated and tapped, is examined and compared with the ideal packing of binary mixtures spherical particles.

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Topics: Particle density (62%), Particle size (52%), Bulk density (51%)

395 Citations

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