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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 B 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. Sillani, F. Published by Emerald Publishing Limited. Anyone may reproduce, distribute, translate and create derivative works of this article for both commercial and non-commercial purposes , subject to full attribution to the original publication and authors. Additive manufacturing AM is attracting strong interest in many industries: production of end-use parts can be achieved within a few hours or days for an increasing number of applications. Powder bed fusion PBF of both polymers and metals is the family of AM technologies that is closest to industrial applications: complex parts with a wide range of properties can be produced on demand and with much more design freedom compared to traditional machining. Recently, the interest of material suppliers to offer new polymer classes and metal alloys has grown. This is due to an overall PBF market growth, mainly driven by industrialization of this family of technologies, which can be estimated by looking at the year-over-year growth of polymer and metal feedstock, which in was Polymer powders are currently produced through different routes: cryogenic milling is the most common technique for short time-to-market products, thanks to its simplicity compared to more complex processes such as dissolution—precipitation. Vetterli reported a regular distribution of spherical particles for polypropylene produced through melt emulsification, and Kleijnen et al. Schmid et al. Vock et al. In AM, for example, the typical flowability metrics are angle of repose gravitational, compression and fluidized flow and compressibility compression and vibration flow Vock et al. For polymers, the flowability measured through the angle of repose is critical for obtaining smooth powder layers and, consequently, an error-free processing Amado, Vetterli reported a positive correlation between the final part density and the powder bed density, highlighting the importance of compressibility in PBM of polymers. Regarding metals, powder flowability Spierings et al. Haferkamp et al. Numerous examples in AM literature Vetterli, ; Vock et al. Kiani et al. The tap density is the packing density of a powder in the highest possible state of compaction. When measuring the tap density according to ASTM B, some information is lost, as powders can have the same Hausner ratio H but different curves when compacting from bulk to tap density. The powders had a similar particle size but, because of their production process, different shape distributions. Scope of the current work is thus to investigate the compaction behavior of a selection of commercially available AM powders, both polymers and metals. The evaluation of the compaction behavior will be carried out with a novel approach on a device specifically designed for this purpose. Repeatability of the aforementioned device is validated, and it will provide additional insights on powder flowability under compression flow compared to the methodologies currently available on the market. This study was carried out on commercially available materials that cover a broad spectrum of size and shape distributions, as highlighted in subsection 3. All materials were tested as received, with no specific conditioning, and their data are reported in Table 1 and Table 2. A DM-6 Leica — Wetzlar, Germany optical microscope was used with the procedure introduced in the study of Sillani et al. The shape was characterized using elliptic smoothness E S after fitting each particle with an ellipse of same area, orientation and centroid as in Figure 4 using the software ImageJ. Using elliptic smoothness for metal feedstock is unusual, as the atomization process typically produces very spherical particles. Nevertheless, being circles a particular case of ellipses, and considering that in this work both polymer and metal feedstock are simultaneously analyzed, the usage of E S seems reasonable in this context. The final setup is depicted in Figure 5. Afterwards, this amount of powder was weighted using a AE balance with a AB measuring unit Mettler Toledo, Schwerzenbach, Switzerland and carefully inserted into the glass cylinder using a funnel. The first frequency was selected to be 0. Compared to the recommended values of 1. Afterwards, each tap was automatically recognized, as highlighted in Figure 7. The subscripts i and x in Figure 7 are counting the taps and video frames, respectively. The measurement was repeated three times for every sample, with avalanches recorded per run. The dynamic angle of repose was calculated for every avalanche, and an average value was used. Then, a linear regression was applied to the first 15 data points to capture the most linear part of the compaction behavior. The performances of modified tapping device introduced in this work had to be statistically evaluated to assess its repeatability. Every material was tested five times by the same operator, and the variance per feedstock was then calculated according to the procedure outlined in Figure 8. The feedstock used for this work was chosen to cover a variety of powder properties and to show the suitability of the proposed methodology to study the flowability of AM materials. Compaction curves for all the powders were measured following the procedure in subsection 2. This means that coarser powders compact slower, possibly because of a lower void fraction after pouring the powder into the container. During the filling procedure, powders with a higher single-particle mass due to higher D 50 V compact more, leading to a lower void fraction and thus exhibiting a lower tapping modulus. Also, during tapping, powders composed of particles with higher mass are more easily dragged down by gravity and thus compact faster. Hence, size and shape distributions of the powder, which are determined by the production process, play a determinant role for flowability, and the data reported in Figure 11 b is confirming that melt emulsification allows to obtain smooth and well-flowing materials Kleijnen et al. Also, as cohesive forces become more important for less dense materials, shape at similar D 50 V also becomes more relevant for the initial packing behavior of polymers. When additional energy is added to the system, e. The flow pattern induced by the tapping setup is different from the one occurring in the rotating drum introduced in subsection 2. In contrast, the compaction flow is different from the fluidized flow for metal samples, for which r is not significant. The standard deviation shows that most of the variance in the powder density is created in the first tens of taps, possibly as a consequence of the cylinder filling procedure based on pouring. To provide some comparison with the ASTM B standard, which is the closest procedure to the methodology proposed in this paper that reported data on inter-laboratory repeatability, the standard deviation of an iron powder is shown in Table 4 , and the results of the present work show improvement by a factor of 2. In the current work, a novel methodology for the evaluation of flowability has been designed, tested and compared with the dynamic angle of repose and Hausner ratio. A commercially available tap density meter was upgraded with a camera that allowed to obtain the change of powder density in real-time. A representative sample of AM feedstock, including both metals and polymers, was chosen for this work through the analysis of four indicators median diameter, elliptic smoothness, avalanche angle and Hausner ratio. The heterogeneity of the samples with respect to the proposed properties was confirmed and hence supports wide applicability of the proposed methodology in the field of AM. It is calculated using a linear regression of the powder compaction over the first 15 taps. This quantity is unique to this test methodology, and correlations with size D 50 V and shape E S factors suggest that different compaction mechanisms exist for polymers and metals. For polymers, shape factors such as E S play a significant role in the flowing behavior of the powder, whereas for metals only the effect of particle size could be shown with the data set at hand. The proposed methodology was evaluated through a repeatability study carried out on all ten powders by one operator, running five measurements for each powder, for a total of 50 measurements. The maximum relative standard deviation is 1. Outlook of the current study is to examine the usage of the settling time, defined as the time between the actual tap and the time at which the final V s e t i is reached, as indicator of powder flowability. Also, an even broader variety of metal powders characterized by different shape e. Furthermore, correlation with in-process performances of each feedstock needs to be carried out. Considering the simplicity of implementing this measurement approach and because of widespread availability and low cost of tap density meters as quality assurance tools, the usage of a camera device has the potential to become a new standard methodology for the evaluation of powder flowability with regards to AM feedstock. Image recognition process from raw data to h t x. Sample output used for image analysis, reporting the powder height in pixel vs time in frames. Flowability comparison with powder properties, divided for polymers left and metals right. Ali , U. Amado , F. Baumann , F. Berretta , S. Caffrey , T. Gotoh , K. Haferkamp , L. Kleijnen , R. Kiani , P. Ramanujan , S. Rietema , K. Sames , W. Schmid , M. Seyda , V. Sillani , F. Spierings , A. Vetterli , M. Vock , S. Ziegelmeier , S. Please share your general feedback. Contact Customer Support. Abstract Purpose Powder bed-based additive manufacturing AM is a promising family of technologies for industrial applications. Findings 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. Figure 1 Different types of flowability expressions. Figure 4 Ellipse fitting. Figure 5 Modified tap density meter. Figure 6 Image recognition process from raw data to h t x. Figure 7 Sample output used for image analysis, reporting the powder height in pixel vs time in frames. Figure 8 Repeatability evaluation outline. Figure 9 Feedstock property space. Figure 10 Compaction behavior. Figure 11 Flowability comparison with powder properties, divided for polymers left and metals right. Francesco Sillani can be contacted at: sillani inspire. Related articles. All feedback is valuable Please share your general feedback. Report an issue or find answers to frequently asked questions Contact Customer Support. EOS Kreilling, Germany. Aspect Tokyo, Japan. Tekna Advanced Materials Inc. Sherbrooke, QC, Canada.

Buying powder Worthersee