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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.
    Holmberg, Jonas
    et al.
    Department of Manufacturing Processes, RISE Research Institutes of Sweden AB, Argongatan 30, Mölndal, Sweden.
    Berglund, Johan
    Department of Manufacturing Processes, RISE Research Institutes of Sweden AB, Argongatan 30, Mölndal, Sweden.
    Brohede, Ulrika
    Department of Production Technology, Swerim AB, Isafjordsgatan 28A, Kista, Sweden.
    Åkerfeldt, Pia
    Division of Material Science, Luleå University of Technology, 971 87, Luleå, Sweden.
    Sandell, Viktor
    Division of Material Science, Luleå University of Technology, 971 87, Luleå, Sweden.
    Rashid, Amir
    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.
    Fischer, Marie
    Department of Industrial and Materials Science, Chalmers University of Technology, Hörsalsvägen 7B, Göteborg, Sweden.
    Hryha, Eduard
    Department of Industrial and Materials Science, Chalmers University of Technology, Hörsalsvägen 7B, Göteborg, Sweden.
    Wiklund, Urban
    Department of Material Science, Ångströmlaboratoriet, Uppsala University, Lägerhyddsvägen 1, Uppsala, Sweden.
    Hassila, Carl Johan Karlsson
    Department of Material Science, Ångströmlaboratoriet, Uppsala University, Lägerhyddsvägen 1, Uppsala, Sweden.
    Hosseini, Seyed
    Department of Manufacturing Processes, RISE Research Institutes of Sweden AB, Argongatan 30, Mölndal, Sweden.
    Machining of additively manufactured alloy 718 in as-built and heat-treated condition: surface integrity and cutting tool wear2023In: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015, Vol. 130, no 3-4, p. 1823-1842Article in journal (Refereed)
    Abstract [en]

    Additive manufacturing (AM) using powder bed fusion is becoming a mature technology that offers great possibilities and design freedom for manufacturing of near net shape components. However, for many gas turbine and aerospace applications, machining is still required, which motivates further research on the machinability and work piece integrity of additive-manufactured superalloys. In this work, turning tests have been performed on components made with both Powder Bed Fusion for Laser Beam (PBF-LB) and Electron Beam (PBF-EB) in as-built and heat-treated conditions. The two AM processes and the respective heat-treatments have generated different microstructural features that have a great impact on both the tool wear and the work piece surface integrity. The results show that the PBF-EB components have relatively lower geometrical accuracy, a rough surface topography, a coarse microstructure with hard precipitates and low residual stresses after printing. Turning of the PBF-EB material results in high cutting tool wear, which induces moderate tensile surface stresses that are balanced by deep compressive stresses and a superficial deformed surface that is greater for the heat-treated material. In comparison, the PBF-LB components have a higher geometrical accuracy, a relatively smooth topography and a fine microstructure, but with high tensile stresses after printing. Machining of PBF-LB material resulted in higher tool wear for the heat-treated material, increase of 49%, and significantly higher tensile surface stresses followed by shallower compressive stresses below the surface compared to the PBF-EB materials, but with no superficially deformed surface. It is further observed an 87% higher tool wear for PBF-EB in as-built condition and 43% in the heat-treated condition compared to the PBF-LB material. These results show that the selection of cutting tools and cutting settings are critical, which requires the development of suitable machining parameters that are designed for the microstructure of the material.

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  • 3.
    Subasic, Mustafa
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Olsson, Mårten
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Dadbakhsh, Sasan
    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.
    Krakhmalev, Pavel
    Department of Engineering and Physics, Karlstad University, 651 88 Karlstad, Sweden.
    Mansour, Rami
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics. Department of Mechanical and Production Engineering, Aarhus University, 8200 Aarhus N, Denmark; DIGIT Center, 8200 Aarhus N, Denmark.
    Fatigue strength improvement of additively manufactured 316L stainless steel with high porosity through preloading2024In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 180, article id 108077Article in journal (Refereed)
    Abstract [en]

    This work investigates the influence of a single tensile preload, applied prior to fatigue testing, on the fatigue strength of 316L stainless steel parts manufactured using laser-based powder bed fusion (PBF-LB) with a porosity of up to 4 %. The specimens were produced in both the horizontal and vertical build directions and were optionally preloaded to 85 % and 110 % of the yield strength before conducting the fatigue tests. The results indicate a clear tendency of improved fatigue life and fatigue limit with increasing overload in both cases. The fatigue limits increased by 25.8 % and 24.6 % for the horizontally and vertically built specimens, respectively. Extensive modelling and experiments confirmed that there was no significant alteration in the shape and size of the porosity before and after preloading. Therefore, the observed enhancement in fatigue performance was primarily attributed to the imposed local compressive residual stresses around the defects.

  • 4.
    Tomkowski, Robert
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Sustainable production development.
    Zhao, Xiaoyu
    KTH, School of Industrial Engineering and Management (ITM), Production engineering, Manufacturing and Metrology Systems.
    Leiro, A.
    Materials Technology YTMN, Scania CV AB, Granparksvägen 10, Södertälje, 151 87, Sweden.
    Archenti, Andreas
    KTH, School of Industrial Engineering and Management (ITM), Sustainable production development.
    Areal topography evaluation of a Ni-based alloy printed by electron beam melting (EBM) process2022In: European Society for Precision Engineering and Nanotechnology, Conference Proceedings: 22nd International Conference and Exhibition, EUSPEN 2022, euspen , 2022, p. 433-436Conference paper (Refereed)
    Abstract [en]

    Electron beam melting (EBM) is a powder bed fusion (PBF) additive manufacturing (AM) process for metal powder printing with wide applications in key industrial sectors, including automotive, healthcare, aerospace, etc. The high-temperature processing of this technique extensively sinters the powders on the surfaces and creates a poor and coarse surface finish. Differences between the surfaces from EBM in comparison with other AM processes make it difficult to answer which measurement method, with what measurement settings, and which evaluation parameters should be used for surface characterization. In this work, the performance of various optical methods for the measurement of areal topography of rough EBM-made metal surfaces was investigated. A specially prepared artefact allowing for the generation of different angles was designed and produced from a nickel-based alloy using EBM without any supporting structure for down-facing surfaces. The as-built up-facing and down-facing surfaces from the artefacts were measured in orthogonal to the build direction. Measurement system capability for as-EBM surfaces is presented along with areal surface texture analysis.

  • 5.
    Trevisan, Silvia
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Wang, Wujun
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Zhao, Xiaoyu
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Laumert, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    A study of metallic coatings on ceramic particles for thermal emissivity control and effective thermal conductivity enhancement in packed bed thermal energy storage2022In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 234, article id 111458Article in journal (Refereed)
    Abstract [en]

    Ceramic particles-based packed bed systems are attracting the interest from various high-temperature applications such as thermal energy storage, nuclear cooling reactors, and catalytic support structures. Considering that these systems work above 600 ◦C, thermal radiation becomes significant or even the major heat transfer mechanism. The use of coatings with different thermal and optical properties could represent a way to tune and enhance the thermodynamic performances of the packed bed systems. In this study, the thermal stability of several metallic (Inconel, Nitinol, and Stainless Steel) based coatings is investigated at both high temperature and cyclic thermal conditions. Consequently, the optical properties and their temperature dependence are measured. The results show that both Nitinol and Stainless Steel coatings have excellent thermal stability at temperatures as high as 1000 ◦C and after multiple thermal cycles. Contrarily, Inconel (particularly 625) based coatings show abundant coating degradation. The investigated coatings also offer a wide range of thermal emissivity (between0.6 and 0.9 in the temperature range of 400–1000 ◦C), and variable trends against increasing temperature. This work is a stepping-stone towards further detailed experimental and modelling studies on the heat transfer enhancement in different ceramic-based packed bed applications through using metallic coatings.

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  • 6.
    Vaddadi, Bhavana
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Centres, Integrated Transport Research Lab, ITRL.
    Zhao, Xiaoyu
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Manufacturing and Metrology Systems.
    Susilo, Yusak
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, System Analysis and Economics. KTH, School of Industrial Engineering and Management (ITM), Centres, Integrated Transport Research Lab, ITRL.
    Nybacka, Mikael
    KTH, School of Industrial Engineering and Management (ITM), Centres, Integrated Transport Research Lab, ITRL.
    Pernestål Brenden, Anna
    KTH, School of Industrial Engineering and Management (ITM), Centres, Integrated Transport Research Lab, ITRL.
    Measuring system level effects of Corporate MaaS: A case study in Sweden2019In: Towards human scale cities -open and happy, 2019, p. 68-Conference paper (Other academic)
    Abstract [en]

    Mobility as a Service (MaaS) integrates different elements of transportation, which mainly are: ticket & payment integration, mobility modes integration and ICT integration. It plays an important role as it is expected to enable the shift from private car use to shared and sustainable transport modes. 

    Corporate Mobility as a Service (CMaaS) is a version of MaaS, which enables mobility within as well as to and from, a work site for the employees. CMaaS fulfils all the above-mentioned characteristics of MaaS. It may also consist of different service packages which could either be free and/ or paid. 

    CMaaS is a new concept and its implementation is limited. The expected benefits of CMaaS are both to support a shift toward sustainable transportation and to be the first step towards more general MaaS solutions. In this paper, we study the effects of CMaaS from economic, environmental and societal aspects on individual, organizational and social levels. 

    The case study of the implementation of CMaaS at a company with 13000 employees located in a city 30 km outside of Stockholm, Sweden, is used in this study. The estate spans over three-square kilometres, and the facilities are spread over the area with distances between the buildings of up to 5kms. 

    The service provides internal taxis, small shuttle buses and e-bikes to aid the employees to get around the estate during the working day. It also offers a commuter bus service to and from Stockholm City. The evaluation is based on data collected through three surveys with more than 400 respondents, complemented with operational data. 

    The analysis is ongoing and will be completed during the spring. Preliminary results show that CMaaS have supported the shift towards the use of e-bikes in favour of motorized modes which has positive effects on e.g. health and emissions. 

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  • 7.
    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.

  • 8.
    Zhao, Xiaoyu
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Manufacturing and Metrology Systems.
    Additive manufacturing of Ni-based Superalloys- an analysis of parameter and strategy driven properties in Electron Beam Melting Process2022Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Metal AM processes produce significantly rough surfaces as compared to wrought or machined components. Currently, the as-EBM surfaces are extremely rough and consequently, the as-built components could not be directly used as commercial products. The state-of-the-art research has focused primarily on deeply machined (DM) samples. The mechanical properties of the EBM components as reported thus are not real representative of the process. This can largely dispute the main merits of the EBM process: print on demand and low buy-to-fly ratio. Hence, the research here was designed to bridge this research gap and systematically analyze the properties of net-shaped (NS) and near-net-shaped (NNS) components.

    This thesis is divided into three levels, including the fundamental, validation and optimization level. The fundamental research work is performed on the commercialized processing parameters from Arcam, for Inconel 718 (IN718). The NNS samples made with and without the commercial multi-spot contour are tested for their mechanical properties. These samples achieved smoother surfaces and better tensile behavior. Thus, they were later compared with the NS and DM samples which were made with the same parameter settings but varied machining depth. The purpose of this work was to test the NS and NNS samples and analyze the cause of the failure. It was found that the premature failure of these samples was linked to the porous surface and subsurface region. Therefore, a machining protocol was set up according to the depth of the porous region which can theoretically improve the tensile strength of the machined samples to a level comparable to wrought material. The findings in case of IN718 were also validated for another superalloy, Inconel 625(IN625). The results again showed that the machining requirement of the as-EBM samples with contour is more than 2 mm. Therefore, a novel contouring strategy was later developed, optimized and tested in order to eliminate the machining requirement. To do so, the continuous contour with different energy, overlapping ratio and sequence to the hatching region was tested. The high-energy continuous contour applied after hatching was found to be the optimal strategy, which was able to maintain a comparable surface condition as the multi-spot contour whilst it could generate a denser subsurface region. Accordingly, the NNS samples with such contour achieved comparable tensile properties as DM samples.

    It should be noted that all these research works were focused on the vertical samples (along the building direction) to avoid high thermal stresses in horizontal direction that seriously limit deformation free manufacturing of the samples. To deal with the challenge of thermal stresses and deformation, the last part of this research was designed to assess the thermal stresses and strains of EBM manufactured IN625 samples. The effects of different processing parameters and scanning strategies were tested to provide a set of guidelines about how to produce the horizontal and longer components. The results showed that one could effectively minimize the thermal stress/strain and deformation of the parts using a bidirectional scanning pattern with proper layer rotations angles to deliver shorter scans in each layer.

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  • 9.
    Zhao, Xiaoyu
    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.
    Contouring strategies to improve the tensile properties and quality of EBM printed Inconel 625 parts2021In: Journal of Manufacturing Processes, ISSN 1526-6125, Vol. 62, p. 418-429Article in journal (Refereed)
    Abstract [en]

    This work systematically analyzes the influence of rough surfaces and porous subsurfaces in electron beam melting (EBM) printed components. Consequently, it applies various contouring strategies to improve the tensile properties of EBM printed Inconel 625 alloy parts. It is shown that no contouring (i.e., only hatching) creates a rough surface with numerous surface voids (as translated to surface notches). Although the commercially used multi-spot contouring can smoothen the surface to some extent (∼34 %), it fails to create a defect-free superficial region by leaving ∼25 % surface voids (translated to large surface notches) and ∼4 % subsurface porosity. These superficial defects form due to an interrupted shrinkage, occurring on the surface and in the contouring region. In contrast, optimal post-hatching high energy continuous contouring creates a thick and consistent post-hatching track that can successfully reconsolidate surface voids remaining from the hatching step. In comparison with the multi-spot contouring, this reduces the surface and subsurface porosity down to ∼10 % and ∼0.4 %, respectively, and hence increases the apparent stiffness by ∼140 %, tensile strength by ∼105 % and elongation by ∼260 %. This nearly reaches the mechanical properties of the conventionally machined parts (UTS ∼635 ± 20 MPa and elongation ∼50 ± 2 %).

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  • 10.
    Zhao, Xiaoyu
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Rashid, Amir
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Machine and Process Technology.
    Dadbakhsh, Sasan
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Influence of Contouring and depth of machining on tensile properties of Inconel 625 made by Electron Beam Melting2019In: Metal Additive Manufacturing Conference: Laser Melting, Electon Beam Melting & Direct Energy Deposition Processes, 2019, p. 118-127Conference paper (Refereed)
    Abstract [en]

    This research is to evaluate the manufacturability and to characterize the performance of Inconel 625 (IN625) by electron beam melting (EBM). After further modifying the commercial EBM parameters for Inconel 718, such as speed function for hatching and the line offset for both hatching and multi-beam contouring, nearly full dense samples (over 99.7% of the wrought material) are produced. It is shown that no contouring strategy generates a relatively rougher surface (approximately 29% in average) compared to the samples printed with contour, requiring even a further post-process machining. Furthermore, the microhardness after EBM is comparable to as-rolled and annealed IN625 material. The samples machined from bulk specimens exhibit good tensile properties regardless of the contouring strategy due to the high depth of machining (5.5mm). However, for the near-net shaped specimens with only 2.1 mm machining of the surfaces, elongation is significantly affected by the contouring strategy. This is in such a manner that the contoured near-net shape parts show relatively 32% less elongation compared to the samples without any contour. Accordingly, multi-beam contouring is better to be avoided to reach tensile properties comparable to the wrought material after a shallow machining, despite the fact that it can lead to a relative smoother surface finish after EBM.

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  • 11.
    Zhao, Xiaoyu
    et al.
    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.
    Strondl, A.
    Swerim AB, Isafjordsgatan 28A, S-16440 Kista, Sweden.
    Hulme-Smith, Christopher
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Process.
    Stenberg, N.
    Swerim AB, Isafjordsgatan 28A, S-16440 Kista, Sweden.
    Dadbakhsh, Sasan
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Manufacturing and Metrology Systems.
    Role of Superficial Defects and Machining Depth in Tensile Properties of Electron Beam Melting (EBM) Made Inconel 7182021In: Journal of materials engineering and performance (Print), ISSN 1059-9495, E-ISSN 1544-1024, Vol. 30, no 3, p. 2091-2101Article in journal (Refereed)
    Abstract [en]

    Since there is no report on the influence of machining depth on electron beam melting (EBM) parts, this paper investigated the role of superficial defects and machining depth in the performance of EBM made Inconel 718 (IN718) samples. Therefore, as-built EBM samples were analyzed against the shallow-machined (i.e., only removal of outer surfaces) and deep-machined (i.e., deep surface removal into the material) parts. It was shown that both as-built and shallow-machined samples had a drastically lower yield strength (970 ± 50 MPa), ultimate tensile stress (1200 ± 40 MPa), and ductility (28 ± 2%) compared to the deep-machined samples. This was since premature failure occurred due to various superficial defects. The superficial defects appeared in two levels, as (1) notches and pores on the surface and (2) irregular pores and cracks within the subsurface. Since the latter occurred down to 2 mm underneath the surface, shallow machining only exposed the subsurface defects to outer surfaces. Thus, the shallow-machined parts achieved only 68% and 8% of UTS and elongation of the deep-machined parts, respectively. This low performance occurred to be comparable to the as-built parts, which failed prematurely due to the high fraction surface voids and notches as well as the subsurface defects.

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  • 12.
    Zhao, Xiaoyu
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Rashid, Amir
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Manufacturing and Metrology Systems.
    Strondl, Annika
    Hulme-Smith, Christopher
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Process.
    Stenberg, Niclas
    Dadbakhsh, Sasan
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Manufacturing and Metrology Systems.
    Role of Superficial Defects and Machining Depthin Tensile Properties of Electron Beam Melting (EBM)Made Inconel 7182021In: Journal of materials engineering and performance (Print), ISSN 1059-9495, E-ISSN 1544-1024Article in journal (Refereed)
    Abstract [en]

    Since there is no report on the influence of machining depth on electron beam melting (EBM) parts, this paper investigated the role of superficial defects and machining depth in the performance of EBM made Inconel 718 (IN718) samples. Therefore, as-built EBM samples were analyzed against the shallow-machined (i.e., only removal of outer surfaces) and deep-machined (i.e., deep surface removal into the material) parts. It was shown that both as-built and shallow-machined samples had a drastically lower yield strength (970 ± 50 MPa), ultimate tensile stress (1200 ± 40 MPa), and ductility (28 ± 2%) compared to the deep-machined samples. This was since premature failure occurred due to various superficial defects. The superficial defects appeared in two levels, as (1) notches and pores on the surface and (2) irregular pores and cracks within the subsurface. Since the latter occurred down to 2 mm underneath the surface, shallow machining only exposed the subsurface defects to outer surfaces. Thus, the shallow-machined parts achieved only 68% and 8% of UTS and elongation of the deep-machined parts, respectively. This low performance occurred to be comparable to the as-built parts, which failed prematurely due to the high fraction surface voids and notches as well as the subsurface defects.

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    Zhao2021_Article_RoleOfSuperficialDefectsAndMac
  • 13.
    Zhao, Xiaoyu
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Production engineering, Manufacturing and Metrology Systems.
    Wei, Yuan
    Northwestern Polytech Univ, Xian Inst Flexible Elect IFE, Xian Inst Biomed Mat & Engn, Frontiers Sci Ctr Flexible Elect, Xian 710072, Peoples R China..
    Mansour, Rami
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    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.
    Effect of Scanning Strategy on Thermal Stresses and Strains during Electron Beam Melting of Inconel 625: Experiment and Simulation2023In: Materials, E-ISSN 1996-1944, Vol. 16, no 1, article id 443Article in journal (Refereed)
    Abstract [en]

    This paper develops a hybrid experimental/simulation method for the first time to assess the thermal stresses generated during electron beam melting (EBM) at high temperatures. The bending and rupture of trusses supporting Inconel 625 alloy panels at similar to 1050 degrees C are experimentally measured for various scanning strategies. The generated thermal stresses and strains are thereafter simulated using the Finite-Element Method (FEM). It is shown that the thermal stresses on the trusses may reach the material UTS without causing failure. Failure is only reached after the part experiences a certain magnitude of plastic strain (similar to 0.33 +/- 0.01 here). As the most influential factor, the plastic strain increases with the scanning length. In addition, it is shown that continuous scanning is necessary since the interrupted chessboard strategy induces cracking at the overlapping regions. Therefore, the associated thermal deformation is to be minimized using a proper layer rotation according to the part length. Although this is similar to the literature reported for selective laser melting (SLM), the effect of scanning pattern is found to differ, as no significant difference in thermal stresses/strains is observed between bidirectional and unidirectional patterns from EBM.

  • 14.
    Zhao, Xiaoyu
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Manufacturing and Metrology Systems.
    Yuan, Wei
    Northwestern Polytechnical University, 127 Youyi W Rd, Bian Jia Cun Shang Ye Jie Qu, Beilin, Xi'an, Shaanxi, China.
    Mansour, Rami
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    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.
    Effect of scanning strategy on thermal stresses and strains during electron beam melting of Inconel 625: experiment and simulation2022In: Article in journal (Other academic)
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