| 1. |
- Hulme-Smith, Christopher, 1989-, et al.
(author)
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A practicable and reliable test for metal powder spreadability : development of test and analysis technique
- 2023
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In: Progress in Additive Manufacturing. - : Springer Nature. - 2363-9512 .- 2363-9520. ; 8:3, s. 505-517
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Journal article (peer-reviewed)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.
(author)
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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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In: Progress in Additive Manufacturing. - : Springer Science and Business Media LLC. - 2363-9520 .- 2363-9512. ; In Press
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Journal article (peer-reviewed)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.
(author)
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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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In: Progress in Additive Manufacturing. - : Springer Science and Business Media LLC. - 2363-9512 .- 2363-9520. ; 7:6, s. 1297-1305
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Research review (peer-reviewed)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. |
- Sheydaeian, Esmat, et al.
(author)
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Effect of pre-heat temperature on enhancing the processability of pure zinc by laser-based powder bed fusion
- 2024
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In: Progress in Additive Manufacturing. - : Springer Science and Business Media Deutschland GmbH. - 2363-9512 .- 2363-9520.
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Journal article (peer-reviewed)abstract
- Zinc-based biomaterials are promising for bioresorbable applications; however, their low melting points pose challenges in laser-based additive manufacturing (AM). This study addresses this challenge by focusing on pre-heat temperature in laser-based powder bed fusion (PBF-LB) AM, a critical factor that significantly impacts final part properties. Unlike previous studies, this work systematically explores the pre-heat temperature’s role in shaping the process map, alongside laser power and scanning speed, for high-density zinc fabrication. The primary goal is to analytically generate parameter sets to avoid the vaporization temperature of zinc during the PBF-LB process and enhance the process’s stability. The proposed approach demonstrates a significant influence of the variation in pre-heat temperature on other input parameters range, such as power and scanning speed, thus enhancing the material’s processability both theoretically and next experimentally. For model validation, 20 specimens divided between three builds each with unique pre-heat temperatures were printed, revealing a direct correlation between increased pre-heat temperature and part density. Remarkably, high density was achieved even with low laser power and high scanning speed, reaching up to 99.96%. This emphasizes the role of pre-heat temperature in enhancing production speed without compromising part integrity. Mechanical properties, assessed by Vickers microhardness (31.4 ± 3.5–39.7 ± 3.3 HV). Control over pre-heat temperature shows promise in influencing part microstructure and grain morphology, critical for future studies.
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| 5. |
- Roos, Stefan, 1983-, et al.
(author)
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Surface roughness reduction in electron beam powder bed fusion additive manufacturing of super duplex stainless steel 2507 : investigating optimisation techniques and face orientation-dependent irregularities
- 2024
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In: Progress in Additive Manufacturing. - : Springer Nature. - 2363-9512.
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Journal article (peer-reviewed)abstract
- The use of additive manufacturing in metals by powder bed fusion via electron beam (PBF-EB) is increasing for fabricating high-quality parts meeting industrial standards. However, high surface roughness poses a consistent challenge in PBF-EB. This study investigates two novel approaches to optimise surface roughness for a given machine and powder combination. Using machine control software’s recently introduced research mode functionality, we develop customised beam control code to effectively explore a vast parameter space. Additionally, we explored the impact of beam travel direction and spot morphology on surface roughness. Line-melt-based contours were explored by specimen manufacturing with layer-wise parameter change, whilst spot-melting-based samples were built using a full factorial design of experiments with four factors at three levels. Initial sample characterisation was done using a stylus-based contact profilometer, followed by detailed evaluation using focus variation microscopy. Results reveal that increasing beam power and spot energy exacerbate surface roughness. We also find that a well-defined energy distribution at the spot's edge contributes to smoother surfaces. Whilst the influence of beam travel direction on surface roughness remains uncertain, our findings underscore the importance of parameter selection in achieving optimal results. By adjusting contouring parameters, we achieve a vertical roughness of Ra17.7 ± 0.9 (Sa 21.6), significantly lower than in the current literature. These findings advance our understanding of surface roughness optimisation in PBF-EB and offer practical insights for improving part quality in industrial applications. By harnessing tailored beam control strategies, manufacturers can enhance the capabilities of additive manufacturing technologies in producing metal components.
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