| 1. |
- Mellin, P., et al.
(författare)
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Bonding EBM-built blocks of 316L steel, using hot isostatic pressing
- 2017
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Ingår i: Proceedings Euro PM 2017: International Powder Metallurgy Congress and Exhibition. - : European Powder Metallurgy Association (EPMA).
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Konferensbidrag (refereegranskat)abstract
- To enable production of the First Wall Beam in the ITER fusion reactor; we attempt to join EBM-built blocks of 316L, by Hot Isostatic Pressing (HIP). For highly critical components, EBM-built material is usually HIPed anyway to heal defects such as pores and cracks. Using HIP to simultaneously bond several print-jobs together into a larger component saves time and reduces manufacturing complexity. We found by carrying out this research, that fine surface roughness is an important enabler for a complete bond. The raw printed surfaces that are obtained straight from the Arcam machine (Ra = 19.2 μm) do not enable a good bond. Instead, traditional machining, which in this paper reached Ra = 2.0 μm, enabled a good bond. HIP parameters are also important. The best bond in this study was achieved after increasing holding time from 1 h to 2 h.
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| 2. |
- Han, Tong, et al.
(författare)
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Characterization of lignin at pre-pyrolysis temperature to investigate its melting problem
- 2019
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Ingår i: Fuel. - : Elsevier. - 0016-2361 .- 1873-7153. ; 235, s. 1061-1069
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Tidskriftsartikel (refereegranskat)abstract
- Technical lignin particles melt under relatively low temperature. This results in the problem in the continuous feeding and fluidization during lignin pyrolysis, which in turn limits its utilization on a large scale. In this study, two most available types of lignin have been used to investigate the lignin melting problem, which are Kraft lignin (KL) from pulping process and hydrolysis lignin (HL) from bio-ethanol production process. Elemental composition, thermal property and thermally decomposed derivatives of each sample are tested by elemental analyzer, TGA, DSC, and Py-GC/MS. Morphology, structure and crystal change before and after heat treatment are tested by microscopy, FTIR and XRD. All results suggest that lignin structure determines its melting properties. Kraft lignin from pulping process contains a less cross-linked structure. It melts under heating. On the other hand, hydrolysis lignin from hydrolysis process contains a highly crossed-linked and condensed structure. It does not melt before decomposition under heat treatment. Modifying lignin structure is suggested for the resolution of technical lignin melting problem.
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| 3. |
- 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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| 4. |
- Hulme-Smith, Christopher, 1989-, et al.
(författare)
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Benchtop Spreadability Measurement of Powder
- 2020
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Ingår i: Proceedings - Euro PM2020 Congress and Exhibition. - : European Powder Metallurgy Association (EPMA).
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Konferensbidrag (refereegranskat)abstract
- The behaviour of metal powders when they are spread into thin layers is critical for powder bed additive manufacturing and other processes. However, there is no accepted test procedure to quantify this behaviour. There is not even an accepted metric that can be used to assess this property. This increases the difficulty of developing new powders for additive manufacturing. The current study proposes test and analysis procedures that minimise the influence of operators and are aimed at providing maximum repeatability and reproducibility while minimising the need for specialist analysis equipment. Initial testing shows that a powder with good flow properties behaves as expected as a function of recoater speeds and always exhibits superior spread metrics to powders with poor flow properties. This provides an important step towards the establishment of a robust, inexpensive test that can help additive manufacturing to grow in new industries.
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| 5. |
- Marchetti, Lorenzo, et al.
(författare)
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Effects of Humidity on the Flowability of Steel Powders
- 2020
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Ingår i: Proceedings - Euro PM2020 Congress and Exhibition. - : European Powder Metallurgy Association (EPMA).
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Konferensbidrag (refereegranskat)abstract
- Humidity and temperature can vary across the world. For this reason, during storage and processing, batches of the same powder may interact with diverse environmental conditions and eventually vary in their properties. For example, a higher atmospheric water vapour content could increase the water adsorbed on the surface of individual powder particles. This adsorbed water can alter the surface interactions between particles, affecting its flow behaviour. In this study, we measured the flow behaviour of various sieve fractions and steel powders in different environmental conditions. We set the environmental conditions in a C1000-40 climate chamber to different levels of relative humidity and temperature. The powder samples and a Freeman FT4 powder rheometer were placed in the climate chamber and equilibrated for 72h. Subsequently, we tested the flow behaviour using two different programs of the powder rheometer. Ultimately, we found that powder flowability is adversely affected by increased humidity.
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| 6. |
- Marchetti, Lorenzo, et al.
(författare)
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Negative impact of humidity on the flowability of steel powders
- 2022
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Ingår i: Particulate Science and Technology. - : Informa UK Limited. - 0272-6351 .- 1548-0046. ; 40:6, s. 722-736
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Tidskriftsartikel (refereegranskat)abstract
- Atmospheric humidity is introduced into powders during handling, transportation, and storage. High moisture content can increase cohesive forces between particles and make it difficult to spread a powder into thin layers in powder bed processes or to fill a mold in processes such as press-and-sinter. Furthermore, water can cause porosity and uptake of oxygen in the final component, damaging its mechanical properties. In this study, a Freeman FT4 powder rheometer was placed inside a climate chamber. Both flowability and shear tests were performed on four steel powders under a range of humidity and temperatures. Basic flowability energy and specific energy were both found to increase significantly with humidity (typically increase by 50% for 80% of relative humidity compared to dry conditions) and were insensitive to temperature change (10–30 °C). Conversely, the behavior of the powders under shear was neither sensitive to relative humidity nor temperature. Measurements of moisture content revealed that finer powders contained more moisture than coarser ones, but the moisture content was not correlated with humidity, probably due to shortcomings with the measurement method. This knowledge can be used to optimize powder processing conditions.
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| 7. |
- Mellin, P., et al.
(författare)
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Environmental and safety aspects of AM metal powder recycling
- 2019
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Ingår i: Euro PM 2019 Congress and Exhibition.
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Konferensbidrag (refereegranskat)abstract
- Repeated recirculation of powder in AM processes ultimately results in a powder with degraded properties. We firstly discuss this topic and describe an experiment designed to understand the mechanisms behind the degradation. Secondly, we perform yield analysis for build jobs on a SLM 125 at RISE IVF. Further on, we consider the required resources and estimate the emitted carbon dioxide equivalents (kgCO2eq) during production of the PBF-LB fraction of two gas atomized powders. The first powder is a tool steel alloy that emits 3.1 kgCO2eq/kg; the second powder is Hastelloy X (HX) that emits 24.2 kgCO2eq/kg. The HX powder, if degraded, is hence very desirable to recycle. Producing 1 kg of PBF-LB fraction from recycled HX material causes 5.7 kgCO2eq vs 24.2 from virgin sources. Finally, we review the health and safety aspects of recirculation and recycling of powder.
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| 8. |
- Mellin, Pelle, et al.
(författare)
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Evaluating flowability of additive manufacturing powders, using the gustavsson flow meter
- 2016
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Ingår i: World PM 2016 Congress and Exhibition. - : European Powder Metallurgy Association (EPMA). - 9781899072484
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Konferensbidrag (refereegranskat)abstract
- The Gustavsson flow meter (including standard ISO-13517) is in this paper used to measure flow rate of fine AM powders. In the current paper, the results are compared to the Hall flow meter and a Freeman FT4 powder rheometer in terms of success of measuring these AM powders. The robustness is clearly superior to the Hall flow meter. Compared to using the rheometer, the Gustavsson flow meter is faster and simpler to use; however, other powder-aspects are evaluated since little correlation was found. All methods of characterizing the flowability could distinguish between (1) two alloys, and (2) if the alloys were new or used (in SLM), and (3) if they were dried or non-dried.
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| 9. |
- Mellin, Pelle, et al.
(författare)
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Evaluating flowability of additive manufacturing powders, using the Gustavsson flow meter
- 2017
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Ingår i: Metal Powder Report. - : Elsevier Ltd. - 0026-0657 .- 1873-4065. ; 72:5, s. 322-326
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Tidskriftsartikel (refereegranskat)abstract
- The Gustavsson flow meter (including standard ISO-13517) is in this paper used to measure flow rate of fine AM powders. In the current paper, the results are compared to the Hall flow meter and a Freeman FT4 powder rheometer in terms of success of measuring these AM powders. The range of possible powders to measure is smaller with Gustavsson flow meter; but in this range, the difference in flow time is greater compared to the Hall flow meter. Compared to using the rheometer, the Gustavsson flow meter is faster and simpler to use; however, other powder-aspects are evaluated since little correlation was found. For the powders in this paper, all methods of characterizing the flowability could distinguish between (1) two alloys, and (2) if the alloys were new or used (in SLM), and (3) if they were dried or non-dried.
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| 10. |
- Mellin, P., et al.
(författare)
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Moisture content analysis of metal powders, using oven desorption followed by Karl Fischer titration
- 2020
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Ingår i: Euro PM 2018 Congress and Exhibition. - 9781899072507
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Konferensbidrag (refereegranskat)abstract
- In this paper, we use Oven Desorption followed by Karl Fischer Titration (KF), to measure moisture content in a newly opened PBF-LB Hasteloy X powder (we found 28.8 ppm), an PBF-EB powder (13.7 ppm) and a HIP powder (6.7 ppm). This method heats a powder sample inside a hermetically closed vial, in an oven. At the same time an inert gas flow enters, flushes out the evaporated water and exits the vial, via a double hollow needle. The gas-water mixture that exits is directed to the Karl Fischer Titration, where the evaporated moisture is quantified. Included is also a comparison with thermogravimetric analysis (TGA) and a climate chamber moisturization experiment of a PBF-LB HX powder followed by KF analysis. After the moisturization and KF analysis, the same powder was characterized in terms of oxygen content.
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