Towards a generally applicable methodology for the characterization of particle properties relevant to processing in powder bed fusion of polymers – From single particle to bulk solid behavior

Hesse, Nicolas; Winzer, Bettina

doi:10.1016/j.addma.2021.101957

Cited by 17 publications

(25 citation statements)

References 54 publications

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“…The Hausner ratio is frequently used as an indicator for flowability [ 25 ] although it is related to the packing density and it might not be a quantity being sufficient to describe subtle changes in bulk solid characteristics altering PBF processability. [ 37 ] Poorly flowing powders frequently have a powder bed with many voids, which results in a low bulk density. By tapping, these voids are filled and the powder will be compacted, resulting in a higher tapped density.…”

Section: Resultsmentioning

confidence: 99%

Infiltration behavior of liquid thermosets in thermoplastic powders for additive manufacturing of polymer composite parts in a combined powder bed fusion process

2021

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Polymer-based multimaterial additive manufacturing (AM) has developed into one of the most promising technologies of recent times. A processing concept was developed in previous studies, which targets the implementation of reactive liquids in a thermoplastic powder-bed for the creation of multimaterial polymer composite parts. This process aims to be the first AM process of its kind to fully utilize the potentials of both thermoplastic and thermoset polymers simultaneously. A highly important aspect for this process is the investigation of the infiltration behavior of the reactive liquids within the powder bed, since premature or delayed curing of the liquids could lead to deviations from the intended geometry as well as process errors due to material protrusions. This investigation presents an experimental and a mathematical approach to describe and predict the time which a droplet needs to completely infiltrate the powder bed. The results showed, that the experimental setup is viable to observe the droplet height over time at temperatures of up to 105 C and infiltration times below 500 ms. The mathematical model proved to be a powerful approximation to describe the infiltration behavior of a reactive liquid within a thermoplastic powder bed once a material-specific form factor is determined for each powder material. Through the process of elimination, the independence of the form factor was demonstrated for different powder parameters like the particle size. A theory is presented, which correlates the form factor to the microstructural shape and surface condition of the particles based on SEM images.

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Section: Resultsmentioning

confidence: 99%

Infiltration behavior of liquid thermosets in thermoplastic powders for additive manufacturing of polymer composite parts in a combined powder bed fusion process

2021

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“…An evaluation of the flowability with the Hausner ratio is limited due to its low methodological sensitivity and lack of transferability to the powder application procedure in LB-PBF-P [ 27 ]. Therefore, ring shear tests deliver more reliable results, as this method is more sensitive to small changes in powder composition [ 33 , 34 ]. Additional measurements of PA12/CNP and PA12/Ag were performed three times to complete the powder characteristics under the same conditions as previous studies [ 20 , 23 ].…”

Section: Methodsmentioning

confidence: 99%

Quality over Quantity: How Different Dispersion Qualities of Minute Amounts of Nano-Additives Affect Material Properties in Powder Bed Fusion of Polyamide 12

et al. 2021

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The great interest, within the fields of research and industry, in enhancing the range and functionality of polymer powders for laser powder bed fusion (LB-PBF-P) increases the need for material modifications. To exploit the full potential of the additivation method of feedstock powders with nanoparticles, the influence of nanoparticles on the LB-PBF process and the material behavior must be understood. In this study, the impact of the quantity and dispersion quality of carbon nanoparticles deposited on polyamide 12 particles is investigated using tensile and cubic specimens manufactured under the same process conditions. The nano-additives are added through dry coating and colloidal deposition. The specimens are analyzed by tensile testing, differential scanning calorimetry, polarized light and electron microscopy, X-ray diffraction, infrared spectroscopy, and micro-computed tomography. The results show that minute amounts (0.005 vol%) of highly dispersed carbon nanoparticles shift the mechanical properties to higher ductility at the expense of tensile strength. Despite changes in crystallinity due to nano-additives, the crystalline phases of polyamide 12 are retained. Layer bonding and part densities strongly depend on the quantity and dispersion quality of the nanoparticles. Nanoparticle loadings for CO2 laser-operated PBF show only minor changes in material properties, while the potential is greater at lower laser wavelengths.

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“…A frequently used approach to assess powder flowability of PBF-LB/P feedstocks, which is even proposed in the relevant norms, is the calculation of the Hausner ratio (HR), the ratio of the tapped density to the (loose) bulk density of the powder. Although giving information on the compaction behavior of a bulk solid, respectively, its cohesion, this quantity may be misleading, because notable changes in tapped density and bulk density are "eliminated" by calculation of the quotient of the two densities, as shown recently (Hesse et al, 2021). Moreover, HR is not very sensitive to subtle changes in bulk properties and completely unreliable, if the compaction is performed manually.…”

Section: Characterization Of Bulk Solid Properties Of Pbf-am Feedstoc...mentioning

confidence: 99%

Dry powder coating in additive manufacturing

Schmidt

Peukert

2022

Front. Chem. Eng.

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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.

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Towards a generally applicable methodology for the characterization of particle properties relevant to processing in powder bed fusion of polymers – From single particle to bulk solid behavior

Cited by 17 publications

References 54 publications

Infiltration behavior of liquid thermosets in thermoplastic powders for additive manufacturing of polymer composite parts in a combined powder bed fusion process

Infiltration behavior of liquid thermosets in thermoplastic powders for additive manufacturing of polymer composite parts in a combined powder bed fusion process

Quality over Quantity: How Different Dispersion Qualities of Minute Amounts of Nano-Additives Affect Material Properties in Powder Bed Fusion of Polyamide 12

Dry powder coating in additive manufacturing

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