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  • 1.
    Dadbakhsh, Sasan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Manufacturing and Metrology Systems.
    Zhao, Xiaoyu
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Manufacturing and Metrology Systems.
    Chinnappan, Prithiv Kumar
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Shanmugam, Vishal
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Zeyu, Lin
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Manufacturing and Metrology Systems.
    Hulme-Smith, Christopher
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Process and geometrical integrity optimization of electron beam melting for copper2022In: CIRP annals, ISSN 0007-8506, E-ISSN 1726-0604, Vol. 71, p. 201-204Article in journal (Refereed)
    Abstract [en]

    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.
    Lin, Zeyu
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Production engineering.
    Surreddi, Kumar Babu
    Materials Technology School of Information and Technology Dalarna University SE‐791 88 Falun Sweden.
    Hulme-Smith, Christopher
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Dadbakhsh, Sasan
    KTH, School of Industrial Engineering and Management (ITM), Production engineering.
    Rashid, Amir
    KTH, School of Industrial Engineering and Management (ITM), Production engineering.
    Influence of Electron Beam Powder Bed Fusion Process Parameters on Transformation Temperatures and Pseudoelasticity of Shape Memory Nickel Titanium2023In: Advanced Engineering Materials, ISSN 1438-1656, E-ISSN 1527-2648Article in journal (Refereed)
    Abstract [en]

    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 post cooling condition. The density of manufactured NiTi parts are investigated with relation to the linear energy input. The results implies 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, densest parts with distinct parameter sets are categorized 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. Among these, a faster cooling rate suppresses phase transformation temperatures, while vacuum cooling combinations do not affect the phase transformation temperatures significantly. All the printed parts in this study exhibit almost 8% pseudoelasticity regardless of the process parameters, while the parts cooled in helium have a higher energy dissipation efficiency ( ), which implies faster damping of oscillations. 

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  • 3.
    Lin, Zeyu
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Manufacturing and Metrology Systems.
    Zhao, Xiaoyun
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Manufacturing and Metrology Systems.
    Dadbakhsh, Sasan
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Manufacturing and Metrology Systems.
    Rashid, Amir
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Manufacturing and Metrology Systems.
    Evaluating the electron beam spot size in electron beam melting machines2021Conference paper (Refereed)
    Abstract [en]

    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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  • 4.
    Yang, Man
    et al.
    Wuhan Univ, Sch Foreign Languages & Literature, Wuhan 430072, Hubei, Peoples R China..
    Bao, Xiangfei
    Wuhan Univ, Sch Foreign Languages & Literature, Wuhan 430072, Hubei, Peoples R China..
    Zeyu, Lin
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Manufacturing and Metrology Systems.
    A STUDY ON THE BASIC PRINCIPLES OF METAPHORICAL THINKING IN MYTHOLOGICAL LANGUAGE AND THE CHANGES OF EMOTIONAL BEHAVIOR2022In: International Journal of Neuropsychopharmacology, ISSN 1461-1457, E-ISSN 1469-5111, Vol. 25, no SUPPL 1, p. A94-A94Article in journal (Other academic)
  • 5.
    Zeyu, Lin
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Manufacturing and Metrology Systems. KTH, School of Industrial Engineering and Management (ITM), Production engineering.
    Electron beam powder bed fusion of Nitinol: A development from production process window towards delicate structures2023Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    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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    Kappa
  • 6.
    Zeyu, Lin
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Manufacturing and Metrology Systems.
    Evaluating the electron beam spot size in electron beam melting for additive manufacturing2021Conference paper (Refereed)
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  • 7.
    Zeyu, Lin
    et al.
    KTH, School of Industrial Engineering and Management (ITM).
    Dadbakhsh, Sasan
    KTH, School of Industrial Engineering and Management (ITM), Production engineering.
    The processing windows for NiTi alloy manufactured by PBF-EBessing windows for NiTi alloy manufactured by PBF-EB2023In: The processing windows for NiTi alloy manufactured by PBF-EB, 2023Conference paper (Other academic)
    Abstract [en]

    Nickel titanium (NiTi) as one of the most utilized shape memory alloy has drawn significant interest due to its unique characteristics. However, NiTi is also considered a susceptible material to smoke during electron beam powder bed fusion (PBF-EB) process, which restricts the manufacturing possibility of the components. This work investigates processing windows for pre-heating and melting of NiTi powder to allow fabricating healthy parts. The smoke tests were carried out at different focus offsets and beam currents in relation to beam speeds. It is noted that a smaller EB spot can effectively prevents smoking while it may cause the strong powder bonding which can affect powder recycling negatively. Thus, a less focused beam (or larger EB spot) was selected to reach medium but efficient sintering. Moreover, it was observed that a negative defocused EB mitigates the smoke phenomenon compared to the positive defocused EB with a similar spot size. After that, parts having a relative density over 99% were successfully manufactured with PBF-EB. It is also found that with the same level of energy input, a set of low power with low scan speed leads to denser parts compared to a set of high power with high scan speed. This is attributed to less complexities in the melt dynamic which is related to lower density of impacting electrons. Besides, the combination of low power with low scan speed also improves geometrical accuracy of the parts attributed to the smaller spot size and smaller melt pool sizes. 

  • 8.
    Zeyu, Lin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Production engineering.
    Dadbakhsh, Sasan
    KTH, School of Industrial Engineering and Management (ITM), Production engineering.
    Larsson, Jokim
    Örebro universitet, Örebro, Sweden.
    Karlsson, Patrik
    Örebro universitet, Örebro, Sweden.
    Rashid, Amir
    KTH, School of Industrial Engineering and Management (ITM), Production engineering.
    A systematic approach to optimize parameters in manufacturing complex lattice structures of NiTi using electron beam PBF processManuscript (preprint) (Other academic)
    Abstract [en]

    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.
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Manufacturing and Metrology Systems.
    Dadbakhsh, Sasan
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Manufacturing and Metrology Systems.
    Rashid, Amir
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Manufacturing and Metrology Systems.
    Developing processing windows for powder pre-heating in electron beam melting2022In: Journal of Manufacturing Processes, ISSN 1526-6125, Vol. 83, p. 180-191Article in journal (Refereed)
    Abstract [en]

    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
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Production engineering.
    Dadbakhsh, Sasan
    KTH, School of Industrial Engineering and Management (ITM), Production engineering.
    Rashid, Amir
    KTH, School of Industrial Engineering and Management (ITM), Production engineering.
    Increasing precision towards NiTi lattice structure using PBF-EB2023Conference paper (Refereed)
    Abstract [en]

    The electron beam powder bed fusion (PBF-EB) is limitedly used to manufacture complex structures such as delicate lattices. Nickel titanium (NiTi) has been chosen for fabricating the lattice structure due to its widely utilization in the biomedical sector. However, issues may arise when manufacturing angled trusses while the dimensional inaccuracy increased with the increasing of the angle between the truss member and the vertical build direction. Therefore, two different scan strategies: spot melting and linear melting were used to manufacture the lattice structures respectively to compare the dimensional accuracy of different structures. This investigation highlights that linear melting is prone to maintain the geometrical accuracy of line-based structure with a limited influence from the scan speed while the spot melting is more capable of manufacturing the point-based structure with a higher geometrical resolution.  

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    Poster
  • 11.
    Zeyu, Lin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Manufacturing and Metrology Systems.
    Zhao, Xiaoyu
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Manufacturing and Metrology Systems.
    Dadbakhsh, Sasan
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Manufacturing and Metrology Systems.
    Rashid, Amir
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Manufacturing and Metrology Systems.
    Evaluation of the electron beam spot size in electron beam melting for additive manufacturing2021In: Laser Metrology and Machine Performance XIV - 14th International Conference and Exhibition on Laser Metrology, Machine Tool, CMM and Robotic Performance, LAMDAMAP 2021, euspen , 2021, p. 89-92Conference paper (Refereed)
    Abstract [en]

    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 measuring EB spot size has been mainly based on printing with/without powder single tracks 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 at a low cost. To do so, a ceramic surface coating was applied to the surface of a copper starting plate and a stainless steel starting plate respectively. Afterwards, the EB applied the tracks onto the coated starting plate and regular metal starting 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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