| 1. |
- Hulme-Smith, Christopher, 1989-, et al.
(författare)
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A practicable and reliable test for metal powder spreadability : development of test and analysis technique
- 2023
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Ingår i: Progress in Additive Manufacturing. - : Springer Nature. - 2363-9512 .- 2363-9520. ; 8:3, s. 505-517
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Tidskriftsartikel (refereegranskat)abstract
- A crucial step in the powder bed metal additive manufacturing process is the formation of a thin layer of powder on top of the existing material. The propensity of the powder to form thin layers under the conditions used in additive manufacturing is critically important, but no test method has yet been established to measure this characteristic, which is sometimes referred to as spreadability. The current work spreads a single layer of powder using commercial equipment from the paint and food industries and derives the density of a layer of powder, which is of a similar thickness to that in additive manufacturing. Twenty-four powders from eight suppliers have been tested and the density of the layers has been measured as a function of various parameters. Twenty-two of the powders successfully form thin layers, with a density of at least 40% of each powder’s apparent density. Hall flow time did not correlate with the spread layer density, although the two powders that did not spread did not pass through the Hall funnel. The roughness of the plate onto which the powder was spread, the recoater speed, the layer thickness, particle size and aspect ratio all affect the measured layer density. Results of the new test are repeatable and reproducible. These findings can be used to develop a test for spreadability for metal powders that can be used for additive manufacturing, which will help to improve the quality of printed components.
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| 2. |
- Mishra, Ases Akas, 1996, et al.
(författare)
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Implementation of viscosity and density models for improved numerical analysis of melt flow dynamics in the nozzle during extrusion-based additive manufacturing
- 2021
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Ingår i: Progress in Additive Manufacturing. - : Springer Science and Business Media LLC. - 2363-9520 .- 2363-9512. ; In Press
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Tidskriftsartikel (refereegranskat)abstract
- Fused Filament Fabrication (FFF) is an Additive Manufacturing (AM) process that builds up a part via layer by layer deposition of polymeric material. The purpose of this study is to implement viscosity and density models for improving the assessment of melt flow behavior inside the nozzle during deposition. Numerical simulations are carried out for different combinations of important process parameters like extrusion velocity Ve, extrusion temperature Te, and filament material (Acrylonitrile Butadiene Styrene (ABS) and Polylactic Acid (PLA)). Cross-Williams–Landel–Ferry (Cross-WLF) viscosity and Pressure–Volume–Temperature (PVT) density models are incorporated to get realistic results. Distribution of printing parameters like pressure, temperature, velocity and viscosity inside the nozzle are observed at steady state and their relationship with the print quality is discussed. Effect of the PVT model on polymer deposition is illustrated by comparing it with deposition considering a constant density. Velocity profiles are obtained for the different cases considered and locations where the flow is fully developed, along the axial distance of the nozzle, are determined and termed as stable zones. A direct correlation between the position of the developed melt flow profile and printing quality is established and the best combination of printing parameters is proposed for ABS and PLA. Extended stable zones are obtained for the polymer melt in the nozzle at Ve = 60 mm/s, Te = 220 °C for ABS and Ve = 30 mm/s and Te = 195 °C for PLA and hence, these can be considered as the optimum values of the printing parameters.
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| 3. |
- Pei, Eujin, et al.
(författare)
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A review of geometric dimensioning and tolerancing (GD&T) of additive manufacturing and powder bed fusion lattices
- 2022
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Ingår i: Progress in Additive Manufacturing. - : Springer Science and Business Media LLC. - 2363-9512 .- 2363-9520. ; 7:6, s. 1297-1305
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Forskningsöversikt (refereegranskat)abstract
- To increase industrial adoption, part qualifcation and certifcation of the additive manufacturing (AM) process are crucial through geometric benchmarking as well as optimising the properties and process parameters. However, an extensive researchgap remains concerning the geometric dimensioning and tolerancing (GD&T) of AM parts. This paper presents a review on the state-of-art GD&T benchmarking of powder bed fusion techniques enabling complex geometrical features like lattices. The study found a lack of design guidelines and standardised measurement techniques for lattice features and profles.
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| 4. |
- Sjöström, William, 1994-, et al.
(författare)
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Melting ceramic Al2O3 powder by electron beam powder bed fusion
- 2024
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Ingår i: Progress in Additive Manufacturing. - : Springer Nature. - 2363-9512.
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Tidskriftsartikel (refereegranskat)abstract
- Electron beam powder bed fusion (PBF-EB) is a known metal additive manufacturing (AM) technology. Processing non-conducting powders such as ceramics has so far been considered as not feasible because of the inherent problems with Coulomb repulsion due to insufficient electrical conductivity. In this study, a method for functionalizing ceramic powder is proposed where particles are electroless coated by a ~ 1 µm Ni layer to decrease the surface resistivity. The feasibility of the suggested approach is tested on Al2O3 powder, and the results show that the coated ceramic powder has a decreased surface resistivity, which enables processing by PBF-EB. Heating and melting parameters were investigated and samples were manufactured at ~ 1600 °C. Sintered and melted powders were analyzed by microscopy and micromechanically tested by nanoindentation. Calculations, visual observation and SEM–EDX suggest that the Ni coating is evaporated during the process, which suggests that the process could be feasible for the manufacturing of pure ceramic parts.
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