| 1. |
- Dadbakhsh, Sasan, et al.
(författare)
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Process and geometrical integrity optimization of electron beam melting for copper
- 2022
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Ingår i: CIRP annals. - : Elsevier BV. - 0007-8506 .- 1726-0604. ; 71, s. 201-204
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Tidskriftsartikel (refereegranskat)abstract
- This work systematically analyzes and optimizes the process of electron beam melting for pure copper. It is shown that, for reliable manufacturing, the preheating temperature should be optimized to avoid porosity as well as part deformation. The electron beam should be fully focused to prevent shrinkage voids (correlated to negative defocusing) and material spattering (linked to positive defocusing). Smoother surfaces from lower hatch spacing (e.g., 100µm) can improve the density reliability, while longer overhangs are reached by a higher hatch spacing. A suitable starting contour strategy is also applied to mitigate border porosities, reduce side roughness and increase geometric precision.
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| 2. |
- Karlsson, Max, et al.
(författare)
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Mixed halide perovskites for spectrally stable and high-efficiency blue light-emitting diodes
- 2021
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 12:1
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Tidskriftsartikel (refereegranskat)abstract
- Bright and efficient blue emission is key to further development of metal halide perovskite light-emitting diodes. Although modifying bromide/chloride composition is straightforward to achieve blue emission, practical implementation of this strategy has been challenging due to poor colour stability and severe photoluminescence quenching. Both detrimental effects become increasingly prominent in perovskites with the high chloride content needed to produce blue emission. Here, we solve these critical challenges in mixed halide perovskites and demonstrate spectrally stable blue perovskite light-emitting diodes over a wide range of emission wavelengths from 490 to 451 nanometres. The emission colour is directly tuned by modifying the halide composition. Particularly, our blue and deep-blue light-emitting diodes based on three-dimensional perovskites show high EQE values of 11.0% and 5.5% with emission peaks at 477 and 467 nm, respectively. These achievements are enabled by a vapour-assisted crystallization technique, which largely mitigates local compositional heterogeneity and ion migration.
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| 3. |
- Lee, Christina, 1992, et al.
(författare)
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Production Across the Nordics
- 2022
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In the uncertain and volatile market that companies are currently facing worldwide, researchers and engineers become a key link to strengthen the industry and universities in order to understand, communicate, and tackle current challenges. In the PhD course, International Production, the goal is to investigate what makes Sweden and Iceland booming industrial hubs driven by technology. Through the visits to different types of industries, such as fintech, medical, or automotive industry, we as researchers have gained a better understanding of the challenges they are currently facing. This report is a summary of our findings and observations. The participants have focused on the six challenge areas highlighted within the Produktion2030 graduate school and summarize their findings as: •Resource-efficient production: Data as a resource is becoming increasingly important for the majority of companies in the Nordics and the application of traditional resource management tools on data is a suggested area for future research. •Flexible production: To strengthen organizations by enabling production systems to be flexible to address market variations is a key challenge to consider in the manufacturing industry •Virtual production development: Digitalization level is distinct in each Nodic country with the reason that each country has its own digitalization transformation policy and different measures on digitalization level. •Humans in the production system: Humans are central in the production systems of the visited companies. Use of automation technology and AI to support humans in their work may become more common in the future. •Circular production systems and maintenance: Circular production systems require a complex approach through the whole value chain. Industry in the Nordics has started the adoption of a circularity approach. •Integrated product and production development: Integration of product and production development is a key business factor for the Nordic countries, and geographical proximity between the two departments can have a beneficial effect. We hope that this report provides more details regarding the success and current challenges of the Swedish and Icelandic enterprises.
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| 4. |
- Lin, Zeyu, et al.
(författare)
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A Systematic Approach to Optimize Parameters in Manufacturing Complex Lattice Structures of NiTi Using Electron Beam Powder Bed Fusion Process
- 2024
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Ingår i: Advanced Engineering Materials. - : Wiley-VCH Verlagsgesellschaft. - 1438-1656 .- 1527-2648. ; 26:10
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Tidskriftsartikel (refereegranskat)abstract
- Herein, the quality and accuracy to manufacture delicate parts from NiTi powder using electron beam powder bed fusion (EB-PBF) technology is investigated. Therefore, benchmarks with thin cylinders and thin walls are designed and fabricated using two distinct scan strategies of EB-PBF manufacturing (i.e., continuous melting and spot melting) with different process parameter sets. After these optimizations, four different lattice structures (i.e., octahedron, cell gyroid, sheet gyroid, and channel) are manufactured and characterized. It is shown both continuous melting and spot melting modes are able to manufacture lattices with relative densities over 97%. And as-built lattice structures exhibit an excellent pseudoelasticity up to 8% depending on the design of the structure, e.g., the channel structure shows more deformation recoverability than the cell gyroid. This is attributed to the integrity of geometry as well as compressive mode of the mechanical loading. Of course, the compressive strength and ultimate compressive strength also increase with the increasing volume fraction. Moreover, the spot melting can be used as an engineering tool to customize a delicate beam-shaped structure with a superior pseudoelasticity.This study explores the precision of electron beam powder bed fusion (EB-PBF) for NiTi parts using continuous and spot melting scan strategies for the density and mechanical properties.image (c) 2024 WILEY-VCH GmbH
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| 5. |
- Lin, Zeyu, et al.
(författare)
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Evaluating the electron beam spot size in electron beam melting machines
- 2021
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Konferensbidrag (refereegranskat)abstract
- Since electron beam (EB) is the main additive manufacturing (AM) tool in electron beam melting (EBM), EB spot size plays a significant role in the parts quality, surface roughness as well as the microstructure and corresponding properties. So far, the research on the relationship between the machine parameters and the EB spot size has been mainly based on the single track and powderless single track printing on a metal plate such as stainless steel. However, this method, due to material thermal properties as well as the melting phenomena, cannot reveal the actual value for the EB spot size. This research is carried out to establish a simple methodology on measuring the EB spot size in a more accurate way with a low cost. To do so, a ceramic surface coating was applied to the surface of a metal copper starting plate and stainless steel plate. Afterwards, the EB applied the tracks onto the coatings and regular metal plate. The analysis showed that the EB tracks on ceramic coated stainless steel plates could be the best replica for the electron beam among those materials tested in this work.
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| 6. |
- Lin, Zeyu, 1991-, et al.
(författare)
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Influence of Electron Beam Powder Bed Fusion Process Parameters on Transformation Temperatures and Pseudoelasticity of Shape Memory Nickel Titanium
- 2023
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Ingår i: Advanced Engineering Materials. - : John Wiley & Sons. - 1438-1656 .- 1527-2648. ; 25:12
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Tidskriftsartikel (refereegranskat)abstract
- Electron beam powder bed fusion (PBF-EB) is used to manufacture dense nickel titanium parts using various parameter sets, including the beam current, scan speed, and postcooling condition. The density of manufactured NiTi parts is investigated in relation to the linear energy input. The results imply that the part density increases with increasing linear energy density to over 98% of the bulk density. With a constant energy input, a combination of low power and low scan speed leads to denser parts. This is attributed to lower electrostatic repulsive forces from lower number density of the impacting electrons. After manufacturing, the densest parts with distinct parameter sets are categorized into three groups: 1) high power with high scan speed and vacuum slow cooling, 2) low power with low scan speed and vacuum slow cooling, and 3) low power with low scan speed and medium cooling rate in helium gas. Among these, a faster cooling rate suppresses phase transformation temperatures, while vacuum cooling combinations do not affect the phase transformation temperatures significantly. Herein, all the printed parts exhibit almost 8% pseudoelasticity regardless of the process parameters, while the parts cooled in helium have a higher energy dissipation efficiency (1 − η), which implies faster damping of oscillations. © 2023 The Authors. Advanced Engineering Materials published by Wiley-VCH GmbH.
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| 7. |
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| 8. |
- Zeyu, Lin, 1991-, et al.
(författare)
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A systematic approach to optimize parameters in manufacturing complex lattice structures of NiTi using electron beam PBF process
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- In this study, the quality and accuracy to manufacture delicate parts from NiTi powder using electron beam powder bed fusion (EB-PBF) technology is investigated. Therefore, benchmarks with thin cylinders and thin walls were designed and fabricated using two distinct scan strategies of EB-PBF manufacturing (i.e., continuous melting and spot melting) with different process parameter sets. After these optimizations, four different lattice structures (i.e., octahedron, cell gyroid, sheet gyroid and channel) were manufactured and characterized. It is shown both continuous melting and spot melting modes are able to manufacture lattices with relative densities over 97%. And, as-built lattice structures exhibit an excellent spring-back up to 8% depending on the design of the structure, e.g., the channel structure shows more deformation recoverability than the cell gyroid. This is attributed to the integrity of geometry as well as compressive mode of the mechanical loading. Of course, the compressive strength and ultimate compressive strength also increases with increasing the volume fraction. Moreover, the spot melting could be used as an engineering tool to customize a delicate beam-shaped structure with a superior pseudoelasticity.
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| 9. |
- Zeyu, Lin, et al.
(författare)
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Developing processing windows for powder pre-heating in electron beam melting
- 2022
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Ingår i: Journal of Manufacturing Processes. - : Elsevier BV. - 1526-6125. ; 83, s. 180-191
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Tidskriftsartikel (refereegranskat)abstract
- Powder pre-heating is a critical step in electron beam melting (EBM), while there has been no systematic work tostudy the corresponding processing windows so far. Accordingly, this work investigates the relation between thesintering and the issues appearing during pre-heating (e.g., smoking or excessive sintering) in EBM of highlysusceptible-to-smoke Nickel-Titanium (NiTi) powder. First, the EB spot size was assessed depending on differentfocus offsets and beam currents from beam tracking experiments on a ceramic-coated stainless steel plate. Af-terwards, the smoke tests were carried out at different focus offsets and beam currents in terms of beam speeds. Itis shown that a smaller EB spot can effectively prevents smoking by enhancing the sintering degree. However,since this high sintering degree can cause strong powder bonding preventing the powder recycling, less focusedbeam (or larger EB spot) was selected to reach medium but efficient sintering in the level of around 30 %.Moreover, due to the influence of the diverging angle on the EB-material interaction, it is found that the negativedefocused EB mitigates the smoke phenomenon compared to the positive defocused EB with a similar spot size.Based on the smoke test results, linked to the sintering degree, the processing windows for pre-heating NiTipowder are developed demonstrating three different modes: smoke-heating, melting-heating and healthy-heating.
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| 10. |
- Zeyu, Lin, 1991-
(författare)
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Electron beam powder bed fusion of Nitinol : A development from production process window towards delicate structures
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Electron beam powder bed fusion (PBF-EB) is increasingly attracting attention for manufacturing the near-net shape parts due to its incomparable merits, such as free residual stress and superior mechanical performance. Nickel Titanium (NiTi) as the most widely used functional alloy, has not been systematically explored for manufacturing using PBF-EB despite the perfect vacuum and high temperature manufacturing environment. Therefore, this research explores the various aspects of PBF-EB for enabling the manufacturing of NiTi parts.The first section, the critical role of powder pre-heating in PBF-EB and its relation to smoking and sintering issues when using highly susceptible-to-smoke NiTi powder is studied. The research includes assessments of the electron beam spot size and its impact on smoking. In addition, this study investigates the influence of defocused electron beams on smoking, with negative defocusing mitigating smoke compared to positive defocusing that may increase the smoking phenomenon. Processing windows for pre-heating NiTi powder are developed based on smoke tests and sintering levels, showing three modes: smoke-heating, melting-heating, and healthy-heating. Accordingly, the healthy-heating processing window is chosen to manufacture the dense NiTi parts.Further, to produce high density and healthy components, the research focuses on investigating the effects of different PBF-EB parameter sets when manufacturing dense NiTi parts, including beam current, scan speed, and cooling conditions. After manufacturing, densest parts with different parameter sets are divided into three groups: i) high power with high scan speed and vacuum slow cooling, ii) low power with low scan speed and vacuum slow cooling and iii) low power with low scan speed and medium cooling rate in helium gas. A combination of low power and low scan speed leads to denser parts. This is attributed to lower electrostatic repulsive forces from lower number density of the impacting electrons. Different cooling conditions are proven to significantly affect phase transformation temperatures. The slower cooling rate leads to a higher Af and Ms temperatures and a wider phase transformation window than those from the parts with the medium cooling rate due to the formation of Ni4Ti3 precipitates. Afterwards, the pseudoelasticity of all the as-built parts is evaluated and illustrated, which shows that correct control of the process can produce components with recoverable strains as high as 8%.The final part of this thesis the quality and accuracy of manufacturing delicate NiTi parts using PBF-EB is studied. Thin cylinders, thin walls, and lattice structures with various designs are manufactured using different scan strategies. The research reveals that both continuous melting and spot melting modes achieve a dense part in delicate structures. As-built lattice structures exhibit excellent spring-back, with the channel structure displaying the most deformation recoverability. The compressive strength and ultimate compressive strength increase with higher volume fractions. Spot melting is demonstrated as a valuable engineering tool for customizing delicate beam-shaped structures with superior pseudoelasticity.
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