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  • 1.
    Alam, Md. Minhaj
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Tuominen, Jari
    Tampere University of Technology.
    Vuoristo, Petri MJ J
    Tampere University of Technology.
    Miettinen, Juha S.
    Tampere University of Technology.
    Poutala, J.
    Department of Mechanics and Design, Tampere University of Technology.
    Näkki, Jonne
    Tampere University of Technology.
    Junkala, J.
    Tampere University of Technology.
    Peltola, Tero
    Tampere University of Technology.
    Surface pore initiated fatigue failure in laser clad components2013Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 25, nr 3Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A laser clad and machined cylindrical structural steel rod was fatigue tested under four-point bending load. The resulting fracture could be tracked back to a spherical surface pore in the Co-based coating. Due to an oxide inclusion, the pore was not identified by dye penetrant inspection. Two circular buckling strain patterns that were detected beside the pore at the surfaces after fracture confirm local plastic deformation prior to crack initiation. In order to calculate the stress field around the surface pore, linear elastic finite element analysis was carried out. For four-point bending load, a surface pore generally exceeds the maximum stress of a smooth rod as long as the pore is located within an azimuthal angle of ±55°, which was the case for the presented as well as for another pore initiated sample.

  • 2.
    Al-Mashikhi, S.O
    et al.
    Salalah College of Technology, Engineering Department, Salalah, Oman and Faculty of Engineering, University of Nottingham.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Voisey, K.T.
    Faculty of Engineering, University of Nottingham.
    Heat affected zones and oxidation marks in fiber laser–oxygen cutting of mild steel2011Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 23, nr 4Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The effect of cutting speed and sheet thickness on surface oxidation and heat affected zones (HAZs) has been investigated for laser–oxygen cutting of mild steel sheet with a fiber laser. Optical and scanning electron micrographs were used to determine the extent of surface oxidation and HAZ from plan and cross-sectional views, respectively. The HAZ is consistently wider at the bottom of the cut compared to the HAZ at the top of the cut. With increasing speed, the width of the HAZ at the top of the cut decreases whereas the HAZ width at the bottom of the cut generally increases. No simple, direct relationship between HAZ width and surface oxidation was seen. However, it is possible to state that in each case considered here, the HAZ would be completely removed if they are machined back by a depth equal to the extent of the surface oxidation.

  • 3.
    Atiyah, H.
    et al.
    Faculty of Engineering, The University of Nottingham.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Petring, D.
    Fraunhofer Institute for Laser Technology ILT.
    Stoyanov, S.
    Fraunhofer Institute for Laser Technology ILT.
    Voisey, T.
    Faculty of Engineering, The University of Nottingham.
    Fiber laser cutting: The use of carbon-filled acrylic as a qualitative and quantitative analysis tool2018Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 30, artikel-id 032009Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The use of carbon-filled black acrylic (CFBA) as a quantitative and qualitative analytical tool for fiber laser cutting is investigated. In the qualitative work, CFBA targets placed below the laser cutting zone when cutting stainless steel showed a distinctive “leaf” shaped evaporation crater which can provide information about the nature of the reflections taking place in the cut zone. Quantitative measurements have revealed a specific evaporation energy of 3.4 J/mm3 for CFBA. However, this figure is only applicable when considering intense beams when the CFBA target is stationary with respect to the laser beam.

  • 4.
    Brueckner, Frank
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. Fraunhofer Institute for Material and Beam Technology.
    Riede, Mirko
    Fraunhofer Institute for Material and Beam Technology.
    Mûller, Michael
    Fraunhofer Institute for Material and Beam Technology.
    Marquardt, Alex
    Fraunhofer Institute for Material and Beam Technology.
    Willner, Robin
    Fraunhofer Institute for Material and Beam Technology.
    Seidel, André
    Fraunhofer Institute for Material and Beam Technology.
    Lopez, Elena
    Fraunhofer Institute for Material and Beam Technology.
    Leyens, Christoph
    Fraunhofer Institute for Material and Beam Technology.
    Beyer, Eckhard
    Fraunhofer Institute for Material and Beam Technology.
    Enhanced manufacturing possibilities using multi-materials in laser metal deposition2018Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 30, nr 3, artikel-id 032308Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Additive manufacturing (AM) addresses various benefits as the buildup of complex shaped parts, the possibility of functional integration, reduced lead times or the use of difficult machinable materials compared to conventional manufacturing possibilities. Beside these advantages, the use of more than one material in a component would strongly increase the field of applications in typical AM branches as energy, aerospace, or medical technology. By means of multi-material buildups, cost-intensive alloys could be only used in high-loaded areas of the part, whereas the remaining part could be fabricated with cheaper compositions. The selection of combined materials strongly depends on the requested thermophysical but also mechanical properties. Within this contribution, examples (e.g., used in the turbine business) show how alloys can be arranged to fit together, e.g., in terms of a well-chosen coefficient of thermal expansion. As can be seen in nature, the multi-material usage can be characterized by sharp intersections from one material to the other (e.g., in case of a thin corrosion protection), but also by graded structures enabling a smoother material transition (e.g., in case of dissimilar materials which are joined together without defects). The latter is shown for an example from aerospace within this paper. Another possibility is the simultaneous placement of several materials, e.g., hard carbide particles placed in a more ductile matrix composition. These particles can be varied in size (e.g., TiC versus WC). Also the ratio between carbides and matrix alloy can be adjusted depending on its application. Especially, nozzle-based free form fabrication technologies, e.g., laser metal deposition, enable the utilization of more than one material. Within this contribution, possibilities to feed more than one filler material are demonstrated. In addition, results of multi-material processes are shown. Finally, this work focuses on different (potential) applications, mainly on power generation, but also for medical technology or wear resistant components.

  • 5.
    Dewi, Handika Sandra
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Volpp, Joerg
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Impact of laser beam oscillation strategies on surface treatment of microalloyed steel2020Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 32, nr 4, artikel-id 042006Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The depth homogeneity of laser-treated zones is one possible factor to define the quality and efficacy of altered mechanical properties in materials. For instance, half-rounded cross-sectional shapes of laser hardened zones using Gaussian beams provide dissimilar hardened depth in the edges and center of the treated area. This means that the in-depth distribution of compressive residual stress varies between the edges and the center of the hardened area. Nonhomogeneity of compressive residual stress distributions can inhibit fatigue properties and can lead to product failure. The utilization of oscillated laser beams has been proven to improve the welding efficiency and energy input distribution to the material, which promises achieving a homogeneous depth of laser-treated zones in hardening applications. Therefore, this work examines the influence of triangular, square, and circular beam oscillation strategies on the energy input distribution during the process and the geometry of the laser-treated zones on microalloyed steel. Laser beam pathways were assembled using a vector graphic editor to visualize the energy distribution from each oscillation strategy. Cross section images of the hardened tracks were taken and related to the thermal energy input profiles. It was revealed that each oscillation strategy demonstrates characteristic temporal and spatial thermal energy input distribution, influencing the geometry of the hardened zone. The circular oscillation strategy produced a widely constant depth in contrary to the triangular and square beam oscillation due to its characteristic energy distribution that allows homogeneous heat dissemination in the material. This confirms that the laser beam oscillation strategy can tailor the energy input distribution to optimize the processing outcome.

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  • 6.
    Eriksson, Ingemar
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Surface tension generated defects in full penetration laser keyhole welding2014Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 26, nr 1, artikel-id 12006Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    During laser keyhole welding of thin plates the melt pool is relatively wide compared to the plate thickness. Under certain conditions an elongated keyhole can be created and a permanent hole is sometimes left in the weld seam. The generation of such holes is determined by surface tension effects in the melt which can generate a self sustaining geometry at the rear of the melt pool. The geometry of the shape is known as a catenoid and has clear geometrical limits.

  • 7.
    Fedina, Tatiana
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Brueckner, Frank
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. Fraunhofer IWS, Winterbergstrasse 28, 01277 Dresden, Germany.
    Kaplan, Alexander F. H.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Wilsnack, Christoph
    Fraunhofer IWS, Winterbergstrasse 28, 01277 Dresden, Germany.
    Laser-assisted reduction of iron ore using aluminum powder2023Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 35, nr 2, artikel-id 022007Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This study reports on the laser-assisted reduction of iron ore waste using Al powder as areducing agent. Due to climate change and the global warming situation, it has become ofparamount importance to search for and/or develop green and sustainable processes for ironand steel production. In this regard, a new method for iron ore utilization is proposed in thiswork, investigating the possibility of iron ore waste reduction via metallothermic reaction withAl powder. Laser processing of iron ore fines was performed, focusing on the Fe2O3-Alinteraction behavior and extent of the iron ore reduction. The reaction between the materialsproceeded in a rather intense uncontrolled manner which led to a formation of Fe-rich domainsand alumina as two separate phases. In addition, a combination of Al2O3 and Fe2O3 melts aswell as transitional areas such as intermetallics were observed, suggesting the occurrence ofincomplete reduction reaction in isolated regions. The reduced iron droplets were prone toacquire a sphere-like shape and concentrated mainly near the surface of the Al2O3 melt or at theinterface with the iron oxide. Both SEM, EDS and WDS analyses were employed to analyzechemical composition, microstructure and morphological appearances of the reaction products.High-speed imaging was used to study the process phenomena and observe differences in themovement behavior of the particles. Furthermore, the measurements acquired from X-raycomputed microtomography revealed that approximately 2.4 % of iron was reduced during thelaser processing of Fe2O3-Al powder bed, most likely due to insufficient reaction time orinappropriate equivalence ratio of the two components.

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  • 8. Forsman, Tomas
    et al.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Magnusson, Claes
    Initiation and termination phenomena in laser welding of aluminum2000Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 12, nr 2, s. 81-84Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This article investigates a defect problem related to laser welding of tailored aluminum blanks. During the initial few millimeters of welding the weld was intermittent. By applying an analytical line source model the weld was shown to experience overheating close to the starting edge. This overheating was reduced by ramping the power during the initial 100 mm and this made the defects disappear. Al sheets of 0.1mm thickness with milled edges were butt welded and bead-on-plate welded in the present investigation.

  • 9.
    Forsman, Tomas
    et al.
    Luleå tekniska universitet.
    Powell, John
    Laser Expertise Ltd., Unit H, Nottingham, England.
    Magnusson, Claes
    Luleå tekniska universitet.
    Process instability in laser welding of aluminum alloys at the boundary of complete penetration2001Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 13, nr 5, s. 193-198Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Intrinsic instabilities in the depth of penetration achieved when laser welding aluminum alloys were investigated in this article. Four types of weld pool configuration, resulting in different welds, were identified, only two of which are associated with full penetration. A simple phenomenological explanation of the unstable welding process at the boundary of complete penetration was proposed. The nature and cause of the instabilities were discussed and suggestions were offered for process control. Materials used: AA6016 aluminum alloy.

  • 10.
    Frostevarg, Jan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Comparison of three different arc modes for laser-arc hybrid welding steel2016Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 28, nr 2, artikel-id 22407Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Traditionally, Laser Arc-Hybrid Welding (LAHW) is made using a gas metal arc heat source in pulsed mode. In this study, welds made with three different arc modes under various conditions are compared. The arc modes compared for LAHW are: Standard, Pulsed, and Cold Metal Transfer (CMT). The pulsed mode, using power modulation, is more controlled than the "natural" Standard mode and offers globular drop transfer with reduced heat input to the work piece, enabling thinner materials to be welded. The CMT arc mode also uses power modulation as well as controlled wire feeding. This enables surface tension drop transfer, involving even less heat input and is also considered to generate less undercuts and spatter than the other two arc modes. The welds compared were made in 7 mm thick S420 laser cut steel sheets with two different welding speeds and gap sizes. They were made using close-to-production setup within the limitations of the CMT capabilities, i.e., low and medium wire feed rates. The weld caps and roots were studied optically and the structures were analyzed by making cross-sectional macrographs longitudinally and transversally. These cross sections were analyzed geometrically, structurally, and also hardness tested. The welds were also studied and analyzed by means of pre- and postweld scanning as well as high speed imaging. The study shows that the laser keyhole reduces the effect of the arc modes, enabling higher welding speeds than without the laser. The gouge formed in front of the keyhole determines occurrence of undercuts and bead uniformity. The material mixing of filler and base material, and laser penetration spiking is also influenced by the depth of the arc gouge. The material structure is also affected to some degrees for expected performances. Even though the short-arc technique CMT show promising results, the pros and cons for each arc technique are discussed

  • 11.
    Frostevarg, Jan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Undercut suppression in laser-arc hybrid welding by melt pool tailoring2014Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 26, nr 3, s. 4-, artikel-id 31501Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In welding, high welding speeds are usually limited by an increase in undercut. This study shows that the geometrical conditions of the melt flow can be tailored to suppress undercut when using the arc leading setup. By applying high speed imaging, it can be seen that the keyhole and its position affects the melt flow, making the distance between the laser and the arc an important parameter. Undercut formation usually occurs due to a narrowing or necking of the melt flow behind the gouge that can be prevented if the melt flow is changed by optimizing the laser/arc positioning

  • 12.
    Frostevarg, Jan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Qinglong, Pan
    Joining and Welding Research Institute, Osaka University.
    Mizutani, Masami
    Joining and Welding Research Institute, Osaka University.
    Kawahito, Yousuke
    Joining and Welding Research Institute, Osaka University.
    Katayama, Seiji
    Joining and Welding Research Institute, Osaka University.
    Effects of edge oxides from laser cutting in laser-arc hybrid welding2018Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 30, nr 1, artikel-id 012014Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Laser-arc hybrid welding (LAHW) is a promising technique for joining sheets due to fast processing speeds and small gap bridgeability. Prior to welding, the edges are often prepared using laser cutting. However, this often leaves small striations with a thin oxide layer that may affect the weld quality. Compared to milled edges, these striations produces a quasigap in a butt joint configuration. The effects of these cutting oxides upon welding are yet unknown. Here, the effects of these oxides in combination with CO2 in the shielding gas are investigated for the LAHW process, using a cold metal transfer arc process.

  • 13.
    Frostevarg, Jan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Torkamany, Mohammad J.
    Department of Materials Engineering, Tarbiat Modares University , P.O. Box 14115-143, Tehran, Iran.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kaplan, Alexander F. H.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Improving weld quality by laser re-melting2014Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 26, nr 4, artikel-id 41502Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Laser welding, arc welding, and laser-arc hybrid welding can all result in undercut and varying penetration. In some cases, it is technically and commercially viable to reduce undercut at the weld cap and smooth out the weld root profile by defocussing the welding laser and using it to remelt the welded surfaces.

  • 14.
    Gedda, Hans
    et al.
    Luleå tekniska universitet.
    Powell, John
    Laser Expertise Ltd., Nottingham, United Kingdom.
    Wahlström, G.
    Duroc AB, Umeå, Sweden.
    Li, W-B
    Luleå tekniska universitet.
    Engström, Hans
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Magnusson, Claes
    Luleå tekniska universitet.
    Energy redistribution during CO2 laser cladding2002Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 14, nr 2, s. 78-82Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This article examines the factors that effect the efficiency of the CO sub 2 -laser powder cladding process. By theoretical calculation and experimental work it has been possible to identify how much of the original laser energy contributes to the cladding process and how much is lost to the surrounding environment by reflection, radiation, convection, etc. Every aspect of energy redistribution has been analyzed and quantified and this has led to a deeper understanding of the process. The article concludes with a number of suggestions for improving the efficiency of blown powder laser cladding.

  • 15.
    Gruber, Samira
    et al.
    Fraunhofer Institute for Material and Beam Technology, IWS, Dresden, Germany. Institute of Materials Science, Technische Universität Dresden,Dresden, Germany.
    Grunert, Christian
    Fraunhofer Institute for Material and Beam Technology, IWS, Dresden, Germany.
    Riede, Mirko
    Fraunhofer Institute for Material and Beam Technology, IWS, Dresden, Germany.
    López, Elena
    Fraunhofer Institute for Material and Beam Technology, IWS, Dresden, Germany.
    Marquardt, Axel
    Institute of Materials Science, Technische Universität Dresden, Dresden, Germany.
    Brückner, Frank
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. Fraunhofer Institute for Material and Beam Technology, IWS, Dresden, Germany.
    Leyens, Christoph
    Fraunhofer Institute for Material and Beam Technology, IWS, Dresden, Germany. Institute of Materials Science, Technische Universität Dresden,Dresden, Germany.
    Comparison of dimensional accuracy and tolerances of powder bed based and nozzle based additive manufacturing processes2020Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 32, nr 3, artikel-id 032016Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Additive manufacturing processes have the potential to produce near-net shaped complex final parts in various industries such as aerospace, medicine, or automotive. Powder bed based and nozzle based processes like laser metal deposition (LMD), laser powder bed fusion (LPBF), and electron beam melting (EBM) are commercially available, but selecting the most suitable process for a specific application remains difficult and mainly depends on the individual know-how within a certain company. Factors such as the material used, part dimension, geometrical features, as well as tolerance requirements contribute to the overall manufacturing costs that need to be economically reasonable compared to conventional processes. Within this contribution, the quantitative analysis of basic geometrical features such as cylinders, thin walls, holes, and cooling channels of a special designed benchmark demonstrator manufactured by LMD; LPBF and EBM are presented to compare the geometrical accuracy within and between these processes to verify existing guidelines, connect the part quality to the process parameters, and demonstrate process-specific limitations. The fabricated specimens are investigated in a comprehensive manner with 3D laser scanning and CT scanning with regard to dimensional and geometrical accuracy of outer and inner features. The obtained results will be discussed and achievable as-built tolerances for assessed demonstrator parts will be classified according to general tolerance classes described [DIN ISO 2768-1,Allgemeintoleranzen-Teil 1: Toleranzen fur Langen- und Winkelmasse ohne einzelne Toleranzeintragung(1991). Accessed 26 February 2018; DIN ISO 2768-2,Allgemeintoleranzen-Teil 2: Toleranzen fur Form und Lage ohne einzelne Toleranzeintragung(1991). Accessed 26 February 2018].

  • 16.
    Gruber, Samira
    et al.
    Fraunhofer Institute for Material and Beam Technology IWS, 01277, Dresden, Germany.
    Stepien, Lukas
    Fraunhofer Institute for Material and Beam Technology IWS, 01277, Dresden, Germany.
    Gerdt, Leonid
    Fraunhofer Institute for Material and Beam Technology IWS, 01277, Dresden, Germany.
    Lopez, Elena
    Fraunhofer Institute for Material and Beam Technology IWS, 01277, Dresden, Germany.
    Kieser, Jan
    Fraunhofer Institute for Material and Beam Technology IWS, 01277, Dresden, Germany.
    Brueckner, Frank
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. Fraunhofer Institute for Material and Beam Technology IWS, 01277, Dresden, Germany.
    Leyens, Christoph
    Fraunhofer Institute for Material and Beam Technology IWS, 01277, Dresden, Germany; TUD Dresden University of Technology, Institute of Materials Science, 01069, Dresden, Germany.
    Bratt, Craig
    Fraunhofer USA—Center Midwest, Laser Applications Division, Plymouth, Michigan 48170, United States.
    Process development for laser powder bed fusion of GRCop-42 using a 515 nm laser source2023Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 35, nr 4, artikel-id 042078Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Copper is widely used in high heat flux and electrical applications because of its excellent electrical and thermal conductivity properties. Alloying elements such as chromium or nickel are added to strengthen the material, especially for higher temperatures. Cu4Cr2Nb, also known as GRCop-42, is a dispersion-strengthened copper-chromium-niobium alloy developed by NASA for high-temperature applications with high thermal and mechanical stresses such as rocket engines. Additive manufacturing (AM) enables applications with complex functionalized geometries and is particularly promising in the aerospace industry. In this contribution, a parametric study was performed for GRCop-42 and the AM process laser powder bed fusion (PBF-LB/M) using a green laser source for two-layer thicknesses of 30 and 60 µm. Density, electrical conductivity, hardness, microstructure, and static mechanical properties were analyzed. Various heat treatments ranging from 400 to 1000 °C and 30 min to 4 h were tested to increase the electrical conductivity and hardness. For both layer thicknesses, dense parameter sets could be obtained with resulting relative densities above 99.8%. Hardness and electrical conductivity could be tailored in the range of 103-219 HV2 and 24%-88% International Annealed Copper Standard (IACS) depending on the heat treatment. The highest ultimate tensile strength (UTS) obtained was 493 MPa. An aging temperature of 700 °C for 30 min showed the best combination of room temperature properties such as electrical conductivity of 83.76%IACS, UTS of 481 MPa, elongation at break (A) at 24%, and hardness of 125 HV2.

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  • 17.
    Haack, M
    et al.
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Kuczyk, M
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Seidel, A
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Lopéz, E
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Brückner, Frank
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. Fraunhofer Institute for Material and Beam Technology, Dresden, Germany. Department of Production Technologies.
    Leyens, C
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany. Institute/Department of Material Science, Technische Universität Dresden, Dresden, Germany.
    Investigation on the formation of grain boundary serrations in additively manufactured superalloy Haynes 2302020Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 32, nr 3, artikel-id 032014Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Solid-solution and carbide-strengthened superalloys such as Haynes 230 are the materials of choice for the hot-section components of gas turbines, e.g., combustion cans and transition ducts. Under severe thermal conditions, to which those parts are exposed, creep strength is a crucial property of the related materials during their lifetime. Recently, the introduction of serrated grain boundaries in Haynes 230 has been intensively studied [J. G. Yoon, H. W. Jeong, Y. S. Yoo, and H. U. Hong, "Influence of initial microstructure on creep deformation behaviors and fracture characteristics of Haynes 230 superalloy at 900 °C,"Mater. Charact. 101, 49-57 (2015); L. Jiang, R. Hu, H. Kou, J. Li, G. Bai, and H. Fu, "The effect of M23C6 carbides on the formation of grain boundary serrations in a wrought Ni-based superalloy,"Mater. Sci. Eng. A 536, 37-44 (2012)], and nearly a triplication of the time to creep failure at high temperature and low stress conditions has been observed [J. G. Yoon, H. W. Jeong, Y. S. Yoo, and H. U. Hong, "Influence of initial microstructure on creep deformation behaviors and fracture characteristics of Haynes 230 superalloy at 900 °C,"Mater. Charact. 101, 49-57 (2015)]. The aim of this paper is to achieve serrated grain boundaries in Haynes 230 through an appropriate thermal process chain including the intrinsic heat treatments of the laser metal deposition (LMD) process, subsequent hot isostatic pressing and suitable heat treatments. The formation of serrations is a relatively new technique for Haynes 230 (i.e., first paper in 2012), and similar alloys and thus serrations have only been introduced in conventionally cast or wrought alloys so far. Optical and scanning electron microscopies are employed in this work to investigate the created microstructures, whose grain and carbide structure is finer compared to the recently studied conventionally processed alloys. Within the LMD samples, serrations were already found on almost all of the observed grain boundaries even in the as-build condition. This result was rather unexpected, as literature reports slow-cooling to be responsible for the formation of serrations, while fast-cooling is prevalent in LMD. Some authors associated the formation of serrations to the precipitation of M23C6-carbides at the grain boundaries during slow cooling conditions [L. Jiang, R. Hu, H. Kou, J. Li, G. Bai, and H. Fu, "The effect of M23C6 carbides on the formation of grain boundary serrations in a wrought Ni-based superalloy,"Mater. Sci. Eng. A 536, 37-44 (2012)]. The lower density of carbides along grain boundaries in the as-build state, however, makes this mechanism seem unlikely. Other authors attributed the emergence of serrations to a phenomenon similar to the faceting mechanism [J. G. Yoon, H. W. Jeong, Y. S. Yoo, and H. U. Hong, "Influence of initial microstructure on creep deformation behaviors and fracture characteristics of Haynes 230 superalloy at 900 °C,"Mater. Charact. 101, 49-57 (2015)]. It can be said that no uniform theory for the emergence of grain boundary serrations exists as of now. The electron backscatter diffraction (EBSD) investigations performed in this work indicated a correlation between serrated grain boundary segments, the {111}-directions of the crystal lattice, and possibly segregations along dendritic subgrain boundaries for a two-dimensional case. Serial sectioning in combination with EBSD analysis confirmed an agreement between the three-dimensional orientation of serrated grain boundary segments and the {111}-direction of adjacent grains. Hence, a mechanism different from the ones described in previous works is proposed for the formation of grain boundary serrations in the additively manufactured Haynes 230 alloy.

  • 18.
    Haglund, Peter
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Eriksson, Ingemar
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Surface tension stabilized laser welding (donut laser welding): A new laser welding technique2013Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 25, nr 3Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A new laser welding process is presented which delivers a porosity free, spatter free weld. The process involves a donut shaped melt with a central hole of the same order of magnitude as the material thickness. The laser illuminates only the leading section of this melt. The hole is kept open by the melt surface tension.

  • 19.
    Harrysson, Ralph
    et al.
    Luleå tekniska universitet.
    Vomacka, P.
    Luleå tekniska universitet.
    Acoustic emission response of soda lime glass after a single Nd-YAG laser pulse1994Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 6, nr 3, s. 153-158Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    When machining brittle solids with a laser, crack formation can occur in the material around the irradiated area causing a strength reduction of the machined material. The purpose of this work was to study a well known brittle material (soda lime glass) by means of acoustic emission (AE) in order to investigate the correlation between visually observed crack formation and detected AE energy released by the crack formation in the material. During and after irradiation of soda lime glass with an Nd-YAG laser pulse, the number of hits and amount of AE energy were measured in the first 300 s using AE. It was found that it is possible to detect AE signals from cracks caused by irradiation with a single Nd-YAG laser pulse. The power of the detected signal is related to the amount of crack formation. Cracks can be minimized or avoided by choosing a suitable combination of pulse time and power density of the single laser pulse. The cracks which occur after a laser shot extend mainly in the radial direction from the irradiated area.

  • 20.
    Heidowitzsch, Maximilian
    et al.
    Fraunhofer Institute for Material and Beam Technology IWS, Winterbergstr. 28, Dresden, Saxony 01277, Germany.
    Gerdt, Leonid
    Fraunhofer Institute for Material and Beam Technology IWS, Winterbergstr. 28, Dresden, Saxony 01277, Germany.
    Samuel, Conrad
    Fraunhofer Institute for Material and Beam Technology IWS, Winterbergstr. 28, Dresden, Saxony 01277, Germany.
    Maetje, Jacob-Florian
    Fraunhofer Institute for Material and Beam Technology IWS, Winterbergstr. 28, Dresden, Saxony 01277, Germany.
    Kaspar, Jörg
    Fraunhofer Institute for Material and Beam Technology IWS, Winterbergstr. 28, Dresden, Saxony 01277, Germany.
    Riede, Mirko
    Fraunhofer Institute for Material and Beam Technology IWS, Winterbergstr. 28, Dresden, Saxony 01277, Germany.
    López, Elena
    Fraunhofer Institute for Material and Beam Technology IWS, Winterbergstr. 28, Dresden, Saxony 01277, Germany.
    Brueckner, Frank
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. Fraunhofer Institute for Material and Beam Technology IWS, Winterbergstr. 28, Dresden, Saxony 01277, Germany.
    Leyens, Christoph
    Fraunhofer Institute for Material and Beam Technology IWS, Winterbergstr. 28, Dresden, Saxony 01277, Germany; Chair of Materials Technology (IfWW), Institute of Materials Science, TU Dresden, Helmholtzstr. 7, Dresden, Saxony 01069, Germany.
    Grain size manipulation by wire laser direct energy deposition of 316L with ultrasonic assistance2023Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 35, nr 3, artikel-id 032017Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The epitaxial growth of coarse and columnar grain structures along the build direction of additive manufactured metals is a usual phenomenon. As a result, as-built components often exhibit pronounced anisotropic mechanical properties, reduced ductility, and, hence, a high cracking susceptibility. To enhance the mechanical properties and processability of additive manufactured parts, the formation of equiaxed and fine grained structures is thought to be most beneficial. In this study, the potential of grain refinement by ultrasonic excitation of the melt pool during laser wire additive manufacturing has been investigated. An ultrasound system was developed and integrated in a laser wire deposition machine. AISI 316L steel was used as a substrate and feedstock material. A conversion of coarse, columnar grains (d(m) = 284.5 mu m) into fine, equiaxed grains (d(m) = 130.4 mu m) and a weakening of typical -fiber texture with increasing amplitude were verified by means of light microscopy, scanning electron microscopy, and electron backscatter diffraction analysis. It was demonstrated that the degree of grain refinement could be controlled by the regulation of ultrasound amplitude. No significant changes in the dendritic structure have been observed. The combination of sonotrode/melt pool direct coupling and the laser wire deposition process represents a pioneering approach and promising strategy to investigate the influence of ultrasound on grain refinement and microstructural tailoring.

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  • 21.
    Ion, John C.
    et al.
    Lappeenranta University of Technology, Lappeenranta, Finland.
    Kokkonen, J.
    Lappeenranta University of Technology, Lappeenranta, Finland.
    A comparison of gas tungsten arc and CO2 laser beam welding of AA20242001Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 13, nr 2, s. 79-83Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Mechanical fastening methods are used extensively to join aluminum alloys, particularly in the aerospace industries. Laser welding provides the possibility of a high productivity single-step process, with the added benefit of potential weight savings of about 10% in comparison with riveting. However, the weldability of many aluminum aerospace alloys is generally considered to be low, and little data are currently available. A procedure for CO2 laser welding of the alloy AA2024 is developed, with the use of 2319 filler wire. Weld property data are shown to achieve the requirements for the most stringent quality level of the current European workmanship standard for laser-welded joints in aluminum. Hardness and tensile strength properties are shown to be similar to those of gas tungsten arc (GTA) welds. The fatigue strength of GTA welds is superior to that of laser welds in the as-welded condition, but when the weld bead is machined flush with the plate surface the difference is reduced. The laser welds achieved the requirements of recommendations produced by the International Institute of Welding for single-sided welding of aluminum alloys. The quality of the weld toe is shown to have the greatest effect on fatigue strength.

  • 22.
    Ivarson, Anders
    et al.
    Luleå tekniska universitet.
    Powell, John
    Luleå tekniska universitet. Laser Expertise Ltd. Nottingham, U.K..
    Magnusson, Claes
    Luleå tekniska universitet.
    Role of oxidation in laser cutting stainless and mild steel1991Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 3, nr 3, s. 41-45Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper gives the results of a detailed examination of the particles ejected from the cut zone during CO2 laser cutting of mild and stainless steels. Cuts were carried out over a range of material thickness at the optimum speed for each at a laser power of 900 Watts. Particles ejected from the cut zone were collected and analyzed to establish their chemical and physical characteristics. Analysis techniques included Scanning Electron Microscopy, wet chemical analysis, optical microscopy, metallography and particle sizing. The results from this extensive analysis have enabled the authors to estimate the heat generated by the oxidation process during cutting of both mild and stainless steels.

  • 23.
    Ivarson, Anders
    et al.
    Luleå tekniska universitet.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik. Laser Expertise Ltd, Nottingham, U.K..
    Magnusson, Claes
    Luleå tekniska universitet.
    Role of oxygen pressure in laser cutting mild steels1996Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 8, nr 4, s. 191-196Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper presents the results of an experimental program investigating the effects of using high pressure oxygen as assist gas in combination with a pulsed laser while cutting medium thick mild steel plates. It was discovered that if the pulse conditions are optimized, the maximum cutting speed for a set average laser power could be increased by up to 10% compared to low oxygen pressure continuous wave (CW) laser cutting. The assist gas was found to have two optimum pressure ranges between which the material suffered from burning on the cut edge. The paper presents a phenomenological model to explain the changes in cut front dynamics as the oxygen pressure is increased and the role of pulsing in suppressing edge burning

  • 24.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Influence of the beam profile formulation when modeling fiber-guided laser welding2011Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 23, nr 4Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    During deep penetration laser welding, the focused laser beam determines the vapor capillary, called keyhole, and in turn the whole process physics. Beside spot diameter and Rayleigh length, the beam profile is another important but hardly explored part of the focused laser beam. The focusing of fiber-guided Yb:fiber, Nd:YAG or diode laser beams creates the complex situation that the beam has a top-hat profile in the focal plane but toward the far field transforms to a Gaussian beam. Such power density distribution was measured for a focused high power Yb:fiber laser beam and then approached by three different beam formulations. The beam formulations were then applied to model the keyhole shape during laser welding. Although a second order beam model approached the measured beam significantly more accurately, the first order Gaussian beam was similarly suitable to predict the keyhole shape as long as the central beam domains do not interact with the material, which occurs only for low focal plane positions. A hypothetical top-hat beam would cause a different, steeper keyhole shape. Consequently, a Gaussian beam is still a suitable formulation for a wide range of welding parameters.

  • 25.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Laser absorptivity on wavy molten metal surfaces: Categorization of different metals and wavelengths2014Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 26, nr 1, artikel-id 12007Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The absorptivity of a laser beam interacting at grazing incidence with the processing front during laser welding, cutting, or drilling depends on the metal to be processed and on the laser wavelength. The absorptivity on a smooth processing front is homogeneously governed by the angle-dependent operating range of the corresponding Fresnel-curve. In contrast, a wavy processing front strongly modulates the absorptivity across the surface. The calculated absorptivity modulation is presented for five different metals and four laser wavelengths. A discussion based on the respective optical constants and Fresnel-curves leads to a categorization of the absorption behavior, mainly dividing into low and high electrical conductivity metals as well as into short and 10.6 μm long laser wavelength. Six categories are distinguished. In particular, highly conductive metals remain highly reflective for short laser wavelength, even for a wavy processing front. Exceptions of higher overall absorptance are Cu for 532 nm and Al for 808 or 532 nm

  • 26.
    Kaplan, Alexander F. H.
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Höfemann, Matthias
    Salzgitter Mannesmann Forschung GmbH, 38239 Salzgitter, Germany.
    Vaamonde, Eva
    AIMEN Technology Center, 36418 Pontevedra, Spain.
    Ramasamy, Anandkumar
    Lincoln Electric Europe, 6534 AD Nijmegen, The Netherlands.
    Kalfsbeek, Bert
    Lincoln Electric Europe, 6534 AD Nijmegen, The Netherlands.
    Näsström, Jonas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Robertson, Stephanie M.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Frostevarg, Jan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Volpp, Jörg
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Microstructures from wire-fed laser welding of high strength steel grades2020Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 32, nr 2, artikel-id 022050Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In welding, wire-feeding enables alteration of the resulting microstructure and, in turn, the mechanical behavior of the welded joint. For pipeline steel grades, very few commercial wires are matching at high strength and simultaneously ensure sufficient toughness. New wire chemistries need to be investigated. Promising consumable chemistries can be studied through metal cored wires. One promising concept is alloys that promote acicular ferrite instead of bainite. Interlocking instead of parallel laths can lead to higher toughness. In the gouge range of 15–19 mm, laser-arc hybrid welding has been studied for pipeline steel grades X80 and X100. For efficient mapping of various weld metal conditions, a simplifying “snapshot” method was developed. A pulse shaped laser beam melts wire pieces in a controlled manner, reproducing thermal cycles in welding. The weld metal tends to form bainite, but under certain conditions, complex microstructures with interlocking laths can be generated. Slow thermal cycles can lead to coalescence of the laths to coarser structures, while fast cycles favored finer structures and occasionally lath interlocking. The formation of acicular ferrite was difficult to achieve. Advanced wire chemistries lowered the hardness of the weld metal, as did preheating.

  • 27.
    Kaplan, Alexander
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kim, Kyounghak
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Bang, Hee-Seon
    Chosun University, Department of Welding & Joining Science Engineering.
    Bang, Han-Sur
    Chosun University, Department of Welding & Joining Science Engineering.
    Näsström, Jonas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Frostevarg, Jan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Narrow gap laser welding by multilayer hot wire addition2016Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 28, nr 2, artikel-id 22410Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Welding of thick section butt joints experiences limitations for different techniques. One option is to fill a narrow gap layer by layer with laser melted wire, a laser metal deposition technique where the complexity of a keyhole is avoided. The presented results show that wire addition can enable relatively thick layers. In particular, when electrically preheating the wire the process becomes more energy-efficient and favorable wetting conditions might be achieved. Since the wire was preheated by an electric current conducted through the wire to the workpiece, high speed imaging has shown that the wire tip can occasionally ignite small electric arcs. The wire deposited in the narrow gap also shows a fluctuating but self-stabilizing movement of the tip. Imperfections that have to be avoided are hot cracks, cavities, lack of fusion, and an irregular final weld surface topology. The technique shows high potential.

  • 28.
    Kaplan, Alexander
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Matti, Ramiz
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Absorption peaks depending on topology of the keyhole front and wavelength2015Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 27, nr Suppl. 2, artikel-id S29012Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    By high speed imaging, wavy patterns were observed at the keyhole front in Yb:fibre laser welding. Despite a regular appearance of downstreaming wave flow in the movies, deeper image analysis shows that the pattern structure is complex. The observed grayscale levels of the flow pattern are likely to correspond to a combination of temperature, topology, and emissivity of the keyhole front, in turn originating from variations of the beam absorption, temperature, boiling, ablation pressure, and melt acceleration across the keyhole surface. Bright domains can fluctuate on a time scale of 10-100 mu s. For interpretation of the fundamental mechanisms, the evidence from high speed imaging analysis is accompanied by mathematical modeling of the absorption modulation, combining local absorptivity, and beam projection. The calculated results show that for a wide range of keyhole topology parameters, lasers with a wavelength of about 1 mu m induce high absorption peaks at the wave shoulders while CO2-lasers have a more homogenizing behavior. Different regimes can be distinguished

  • 29.
    Kaplan, Alexander
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Spatter in laser welding2011Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 23, nr 3Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Spatter, the ejection of melt from a weld pool, is a major problem whenever it occurs in a welding process. The ejection of droplets from the weld metal results in a weld with underfill, undercuts, craters, blowholes, or blowouts-all of which can have a detrimental effect on the mechanical properties of the weld. This paper presents a systematic description of the different types of spatter phenomena which occur during laser welding. A categorization system is proposed to facilitate the comparison and combination of research findings on spatter. This should allow researchers in this area to act as a more effective team in future

  • 30.
    Kledwig, Christian
    et al.
    Development Department, Sauer GmbH LASERTEC, DMG MORI AG, Pfronten 87459, Germany.
    Perfahl, Holger
    Development Department, Sauer GmbH LASERTEC, DMG MORI AG, Pfronten 87459, Germany.
    Reisacher, Martin
    Development Department, Sauer GmbH LASERTEC, DMG MORI AG, Pfronten 87459, Germany.
    Brückner, Frank
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. Additive Manufacturing and Printing, Fraunhofer Institute for Material and Beam Technology IWS, Dresden 01277, Germany.
    Bliedtner, Jens
    SciTec Department, Ernst-Abbe-Hochschule Jena, Jena 07745, Germany.
    Leyens, Christoph
    Additive Manufacturing and Printing, Fraunhofer Institute for Material and Beam Technology IWS, Dresden 01277, Germany. Institute of Materials Science, Technische Universität Dresden, Dresden 01062, Germany.
    Image-based algorithm for nozzle adhesion detection in powder-fed directed-energy deposition2020Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 32, nr 2, artikel-id 022021Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The rapidly growing technological innovation of directed energy deposition leads to an increase in part complexity as well as quality and mechanical properties of manufacturable components. However, the variety of process parameters and influencing factors still requires skilled operators, who observe the machine tools. For an unobserved use of deposition welding machines, well parametrized and validated monitoring systems have to analyze the process to detect irregularities and finally initiate a machine stop. This study focuses on nozzle adhesions that frequently occur when tool or high-speed steels are processed. This effect leads to decreasing quality or ultimately to a failure of the whole welding process. In this work, the authors present an algorithm and the corresponding parametrization to automatically detect nozzle adhesions based on images from a coaxial camera, integrated in the laser head. The algorithm is based on a detailed image analysis from which temporal and spatial patterns are derived. In particular, the algorithm calculates a nozzle adhesion indicator based on the heat intensity distribution in an experimentally derived shaped area on the inner nozzle boundary. It is parametrized in such a way that process-critical adhesions are detected. The algorithm was parametrized using an experimental setup with four materials: stainless steel (X2CrNiMo17-12-2), tool steel (X35CrMoMn7-2-1), high-speed steel (HS6-5-2C), and the nickel-based alloy NiCr19NbMo.

  • 31.
    Koh, Y.S.
    et al.
    Kiruna Center for Conservation of Cultural Property.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Removal of layers of corrosion from steel surfaces: a qualitative comparison of laser methods and mechanical techniques2007Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 19, nr 2, s. 99-106Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A series of steel substrates with precisely grooved surfaces were produced and subsequently corroded under controlled conditions. The oxidized surfaces were then cleaned by one of eight methods, three of which were mechanical (brushing, micro blasting with Al2O3 or glass) and five of which were laser dependent (TEA CO2 or Nd:YAG laser with or without surface water). Surface profilometry and scanning electron microscopy have been used to compare the cleaned surfaces with the original surface geometries. The relative efficacy of the eight cleaning methods has been qualitatively compared for three different types of grooved surface and three different levels of corrosion

  • 32.
    Kolsch, N.
    et al.
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Seidel, A.
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Finaske, T.
    Fraunhofer Institute for Material and Beam Technology , Winterbergstraße 28, 01277 Dresden, Germany.
    Brueckner, Frank
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Gumpinger, J.
    European Space Research and Technology Centre—ESTEC, Noordwijk, Netherlands.
    Bavdaz, M.
    European Space Research and Technology Centre—ESTEC, Noordwijk, Netherlands.
    Rohr, T.
    European Space Research and Technology Centre—ESTEC, Noordwijk, Netherlands.
    Ghidini, T.
    European Space Research and Technology Centre—ESTEC, Noordwijk, Netherlands.
    Leyens, C.
    Fraunhofer Institute for Material and Beam Technology , Winterbergstraße 28, 01277 Dresden, Germany; Institute of Materials Science, Technische Universität Dresden, Helmholtzstr. 7, 01069 Dresden, Germany.
    Novel local shielding approach for the laser welding based additive manufacturing of large structural space components from titanium2020Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 32, nr 2, artikel-id 022075Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Advanced Telescope for High-ENergy Astrophysics (ATHENA) will observe “the hot and energetic universe,” which was determined as one of the most urgent scientific topics for a major future space mission by The European Space Agency (ESA). One of its three main components is the optical bench, a monolithic titanium structure that accommodates 678 mirror modules and keeps them accurately aligned. The immense but slender structure in the range of 2.5–3 m diameter at a height of 300 mm proves a challenge to manufacturing. A hybrid robot cell is developed using additive buildup via laser welding, combined with high-performance machining and the state of the art process and metrology monitoring and control. The present work focuses on the shielding of the laser induced melt pool, a key concern when processing titanium. The sensitive metal with unusual low heat conductivity requires a large area of high purity atmosphere to prevent embrittlement. However, the large hybrid system prohibits the use of a sealed enclosure, and therefore, a local shielding system is developed for the challenging case of the ATHENA optical bench’s hollow-chamber design. Since the present thin wall design poses a worst-case scenario in terms of heat dissipation and shielding flow for the shielding system, its effectiveness here can be applied to most other geometries enabling the flexibility for lot size one. The key features of the novel approach are the prevention of turbulence while keeping operation economical despite the large shielding area. The first is achieved by means of an integrated honeycomb screen and the latter by employing a layered flow with a higher velocity outer curtain and an air deflecting coflow. This system was numerically optimized, tested, and effectiveness proven by means of visual inspection, microstructural analysis, and measurement of material properties.

  • 33.
    Koti, Daniel
    et al.
    Faculty of Engineering, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom.
    Powell, John
    Faculty of Engineering, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom; University of Stuttgart, ICM, D-70569 Stuttgart, Germany.
    Naesstroem, Himani
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Spaccapaniccia, Chiara
    Independent Researcher.
    Voisey, K. T.
    Faculty of Engineering, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom.
    Laser cladding: A high-speed-imaging examination of powder catchment efficiency as a function of the melt pool geometry and its position under the powder stream2023Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 35, nr 4, artikel-id 042065Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper provides quantitative information about the paths taken by blown powder particles during laser cladding. A proportion of the powder is "wasted" by bouncing off the solid areas surrounding the melt pool. This wastage reduces the productivity and profitability of the process. In this paper, specially developed software was used to analyze high-speed imaging videos of the cladding process, to monitor the directions of powder particle flight toward and away from the melt pool area. This information has been correlated to the geometry and position of the melt pool zone for three different cladding techniques: single track cladding (A tracks), standard overlapping track cladding (AAA cladding), and a recently developed technique called ABA cladding. The results show that the melt pool geometry, and particularly the overlap between the melt pool and the incoming powder stream, has a strong influence on powder catchment efficiency. ABA cladding was found to have considerably better powder catchment efficiency than standard AAA cladding and this improvement can be explained by consideration of the geometries and positions of the melt pools and surrounding solid material in each case. As powder costs are an important factor in industrial laser cladding, the adaption of the ABA technique, and/or control of pool/powder stream overlap (e.g., by making the powder stream not coaxial with the laser beam), could improve the profitability of the process.

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  • 34.
    Koti, Daniel
    et al.
    Faculty of Engineering, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom.
    Powell, John
    Faculty of Engineering, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom; Innovation Campus Future Mobility, University of Stuttgart, ICM, D-70569 Stuttgart, Germany.
    Naesstroem, Himani
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Voisey, K. T.
    Faculty of Engineering, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom.
    Powder catchment efficiency in laser cladding (directed energy deposition). An investigation into standard laser cladding and the ABA cladding technique2023Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 35, nr 1, artikel-id 012025Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper investigates the efficiency of powder catchment in blown powder laser cladding (a directed energy deposition technique). A comparison is made between standard "track by overlapping track"cladding ("AAA"cladding) and "ABA"cladding, where the gaps left between an initial set of widely spaced tracks ("A"tracks), are filled in by subsequent "B"tracks. In both these techniques, the melt pool surface is the collection area for the cladding powder, and the shape of this pool can be affected by several parameters including cladding speed, intertrack spacing, and type of cladding technique. The results presented here are derived from of an analysis of high-speed videos taken during processing and cross sections of the resultant clad tracks. The results show that the first track in AAA cladding has a different melt pool shape to subsequent tracks, and that the asymmetry of the subsequent track melt pools results in a reduction in the powder catchment efficiency. In contrast to this, the geometry of the "B"track melt pools between their adjacent "A"tracks results in an enhanced powder catchment efficiency.

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  • 35.
    Lamas, Javier
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. Centro Tecnolóxico do Naval Galego, Ferrol, Spain.
    Karlsson, Jan Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Norman, Peter
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kaplan, Alexander F. H.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Yañez, Armando
    Centro de Investigacións Tecnolóxicas, Universidade da Coruña, Ferrol 15403 (A Coruña), Spain.
    The effect of fit-up geometry on melt flow and weld quality in laser hybrid welding2013Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 25, nr 3Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Hybrid laser-arc welding has a good tolerance to poor fit up as compared to simple laser welding. For a butt joint, the joint fit-up variations can be reduced to two local properties: the gap width and the vertical edge mismatch. The impact of these two properties on the resulting weld quality has been studied systematically in this paper. The original edges as well as the resulting weld surface topography have been scanned in three dimensions in order to study trends. During hybrid welding, the melt flow and the electric arc were observed at the top surface by high speed imaging to analyze the complex fluid flow phenomena.

  • 36.
    Laskin, Alexander
    et al.
    AdlOptica GmbH, Rudower Chaussee 29, 12489 Berlin, Germany.
    Volpp, Joerg
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Comparison of the thermal focus shift and aberration between the single-mode and multimode lasers2021Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 33, nr 4, artikel-id 042026Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Thermal lensing is a well-known but typically undesired effect during the use of laser optics. Nonuniform (gradient) heating due to absorption of high-power laser radiation in optical elements causes thermal lensing, paraxial focus shift, and aberration leading to changes in size and intensity profile of the focused spot in optics. Therefore, an analysis of primary physical effects of geometrical deformation of optical surfaces in the form of aspheric bulges and transformation of the material into a gradient refractive medium was conducted to quantitatively estimate the focus shift and aberrations. Since focus shift effects are different in the case of single-mode and multimode lasers, for both laser modes, the optimal relationships between the physical properties of optical materials for reduction in thermo-optical effects through compensating the material thermal expansion by the change in the refractive index—condition of self-compensation or athermalization were formulated. A comparison of the characteristics, namely, temperature coefficient of the optical pathlength and thermo-optical ratio allowed determination of the optimal materials for the optics for both single-mode and multimode high-power lasers: athermal crystalline quartz and specialty glasses, sapphire with extremely high thermal conductivity ensure minimal temperature gradients. Optics made of these materials exhibit a minimized thermal focus shift and aberration even during the absorption of laser energy in the bulk material and coatings by contamination, scratches, and other surface defects. Weak birefringence of crystalline quartz and sapphire does not prevent their successive use in laser optics.

  • 37.
    Laskin, Alexander
    et al.
    AdlOptica GmbH, Rudower Chaussee 29, 12489 Berlin, Germany.
    Volpp, Joerg
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Laskin, Vadim
    AdlOptica GmbH, Rudower Chaussee 29, 12489 Berlin, Germany.
    Nara, Takuji
    Profitet, 3-1-13, Tokiwa, Urawa-ku, Saitama-shi, Saitama-ken 330-0061, Japan.
    Jung, Seong Ryol
    ShinHoTek, #1306, 19 Gasan digital 1-ro, Geumcheon-gu, Seoul 08594, South Korea.
    Multispot optics for beam shaping of high-power single-mode and multimode lasers2021Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 33, nr 4Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The performance of various laser technologies, such as welding, laser powder bed fusion (LPBF), brazing, cladding, and sheet metal cutting, based on the use of high-power multimode fiber lasers, fiber-coupled solid-state, and diode lasers, can be improved using the patent pending beam-shaping optics providing optimal energy distributions by splitting the laser beam into several separate spots in the working plane and variable energy sharing between these spots. Various patterns, such as square, line, and rhombus, consisting of four or nine separate spots, are expected to eliminate or reduce spatter and to realize optimum temperature distributions in the melt pool and stabilizing the processes in the welding of tailored blanks, copper and aluminum parts in the production of batteries, zinc-coated steel, cladding, and LPBF. Because multimode lasers have a comparably low spatial coherence characterized by large beam parameter products or beam quality (M²) values, it is difficult to control the intensity distribution by methods other than imaging the fiber end with a collimator and a focusing objective. The proposed solution is a combination of fiber end imaging and geometrical separation of focused spots perpendicular to the optical axis using special optical components and creating a working spot as a combination of several spots. Varying the energy portions in separate spots and the distances between them make it possible to optimize common spot intensity distributions for particular applications. To ensure reliable operation with multi-kW lasers, the refractive optical components of the multispot devices are implemented from athermal optical materials characterized by insignificant thermal lensing and, hence, negligible thermal focus shift and spherical aberration. The article presents descriptions of multispot optics and examples of intensity profile measurements and application results, while the reduction in spattering was observed using multispot laser welding. It is concluded that the melt pool flows homogenize when applying several laser spots compared to a single spot. The possibility of tailoring melt pool dimensions in LPBF was shown.

  • 38.
    Lopez, Elena
    et al.
    Fraunhofer Institute for Material and Beam Technology , Winterbergstraße 28, 01277 Dresden, Germany.
    Felgueiras, Tomás
    Fraunhofer Institute for Material and Beam Technology , Winterbergstraße 28, 01277 Dresden, Germany.
    Grunert, Christian
    Fraunhofer Institute for Material and Beam Technology , Winterbergstraße 28, 01277 Dresden, Germany.
    Brueckner, Frank
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. Fraunhofer Institute for Material and Beam Technology , Winterbergstraße 28, 01277 Dresden, Germany.
    Riede, Mirko
    Fraunhofer Institute for Material and Beam Technology , Winterbergstraße 28, 01277 Dresden, Germany.
    Seidel, André
    Fraunhofer Institute for Material and Beam Technology , Winterbergstraße 28, 01277 Dresden, Germany; Dresden University of Technology , 01062 Dresden, Germany.
    Marquardt, Alex
    Dresden University of Technology , 01062 Dresden, Germany.
    Leyens, Christoph
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik. Fraunhofer Institute for Material and Beam Technology , Winterbergstraße 28, 01277 Dresden, Germany.
    Beyer, Eckhard
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik. Fraunhofer Institute for Material and Beam Technology , Winterbergstraße 28, 01277 Dresden, Germany.
    Evaluation of 3D-printed parts by means of high-performance computer tomography2018Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 30, nr 3, artikel-id 032307Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Conventional tactile and optical testing methods are not capable to detect complex inner geometries or complex surface shapes. Detecting porosities in parts is also not possible with those nondestructive methods. Among other material parameters, geometrical accuracy is essential to determine part's quality. Additive manufacturing processes also have to be optimized regarding geometry deviations caused by distortion or unfavorable orientation in the build chamber. For additive manufactured parts that incorporate previously mentioned features, high-performance computer tomography is the more suitable nondestructive testing method. Components of different materials such as plastics, ceramics, composites, or metals can be completely characterized. This nondestructive testing method was used for porosity analysis regarding the shape and local distribution of pores in an additive manufactured part to find correlations concerning the most suitable process conditions. The measured part data were also compared to original CAD files to determine zones of deviation and apply specific process strategies to avoid distortion. This paper discusses the results of integrating high-performance computer tomography (power: 500 W, max. part size: Ø 300 mm, 300 × 430 mm2) in a productionlike environment of additively manufactured parts for a wide range of technologies (i.e., electron beam melting and selective laser melting). I. INTRODUCTION

  • 39.
    Mishra, Pragya
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Ilar, Torbjörn
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Brueckner, Frank
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Energy efficiency contributions and losses during selective laser melting2018Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 30, nr 3, artikel-id 032304Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Selective Laser Melting technique, SLM, requires remelting of adjacent tracks to avoid cavities and other imperfections. Usually, very conservative process parameters are chosen to avoid imperfections, resulting in a low building rate. The process efficiency relates the energy required for the generation of a new track to the laser beam power. For SLM this efficiency is determined by the process parameters, specifically hatch distance, layer depth and scanning speed, independent of the resulting process mechanisms. For SLM the process efficiency often very low, typically 2‑20%. Apart from beam reflection losses of normally 50-60%, significant energy losses result from the remelting of surrounding layers. Some areas can even experience multiple remelting cycles. Further losses originate inevitably from substrate heating. A simplified mathematical model of the track cross section and the corresponding layer overlap geometry has been developed, to analyze the different loss contributions from remelting with respect to the process parameters. The model explains why increasing the hatch distance or the layer depth proportionally increases the process efficiency. However, these increases are limited by cavity formation. The cross section of the overlapping tracks generated by SLM can be regarded as an experimental fingerprint linked to the process conditions. The track cross section geometries can significantly fluctuate, in terms of area and coordinate position. The fluctuations require additional reduction of the hatch distance or layer depth, to ensure robust, cavity-free processing. Examples are presented for stainless steel where a 180 W laser beam has led to a process efficiency of 5-11%, proportional to a hatch distance that was increased from 50 to 110 µm, for 40 µm powder layer depth, at a speed of 50 m/min.

  • 40.
    Moradi, Mahmoud
    et al.
    Department of Mechanical Engineering, Faculty of Engineering, Malayer University.
    Salimi, Nahid
    Department of Computer Engineering, Malayer Branch, Islamic Azad University.
    Ghoreishi, M.
    Faculty of Mechanical Engineering, K.N. Toosi University of Technology, Tehran.
    Abdollahi, Hadi
    Department of Mechanical Engineering, Urmia University of Technology.
    Shamsborhan, Mahmoud
    Department of Engineering, Mahabad Branch, Islamic Azad University.
    Frostevarg, Jan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Ilar, Torbjörn
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Parameter dependencies in laser hybrid arc welding by design of experiments and by a mass balance2014Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 26, nr 2, artikel-id 22004Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Reinforcement, undercut, and root drop-through during laser hybrid arc welding of steel were studied in dependence of gap width, welding speed, and wire feeding rate. Generalized trends were obtained through design of experiments. Most of the trends could be explained by a mass balance while some parameter impacts relied on more complex mechanisms. In particular, different levels of complexity of parameter dependencies were distinguished, ranging from monotonous behaviour to maxima and to changing signs of the trends. The findings are of high practical relevance to optimize the process with respect to the weld quality. Moreover, the potential and limits of the design of experiments method, of a mass balance, and of the matrix flow chart method are discussed.

  • 41.
    Moritz, J.
    et al.
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Seidel, A.
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Braun, B.
    Space Structures GmbH, Berlin, Germany.
    Brandao, A.
    European Space Research and Technology Centre, ESTEC, Noordwijk, Netherlands.
    Pambaguian, L.
    European Space Research and Technology Centre, ESTEC, Noordwijk, Netherlands.
    Köhler, B.
    Fraunhofer Institute for Ceramic Technologies and Systems, Dresden, Germany.
    Barth, M.
    Fraunhofer Institute for Ceramic Technologies and Systems, Dresden, Germany.
    Riede, M.
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Lopéz, E.
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Brückner, Frank
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Leyens, C.
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.Institute of Materials Science IfWW, Technische Universität Dresden, Dresden, Germany.
    Functional integration approaches via laser powder bed processing2019Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 31, nr 2, artikel-id 022319Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Additive manufacturing design rules are different from those of conventional fabrication techniques. These allow geometries that would not be possible to achieve otherwise. One example of application is the integration of functional parts as part of the manufacturing process. Conceivable applications range from mechanical functions like integration of moving parts or thermodynamic functions, for example, cooling channels or incorporation of electric circuits for electrical functionalization [J. Glasschroeder, E. Prager, and M. F. Zaeh, Rapid Prototyping J. 21, 207–215 (2015)]. Nevertheless, the potential of functional integration using powder-bed processes is far from being exhausted. The present approach addresses the generation of inner cavities and internal structures of titanium-based parts or components by the use of selective laser melting. This paper focusses on the investigation of voids and cavities regarding their capabilities to add new functions to the material. To this end, comprehensive characterization is performed using destructive as well as nondestructive testing methods. These include 3D scanning, computed tomography, and surface roughness measurements as well as microscopic analysis. Voids and cavities were filled with different thermoplastic materials, followed by the qualitative assessment of the mold filling and resulting material properties. Finally, applications are derived and evaluated with respect to the field of lightweight design or damping structures.

  • 42.
    Mueller, Michael
    et al.
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany; Technische Universität Dresden, Dresden, Germany.
    Riede, Mirko
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Eberle, Sebastian
    Kampf Telescope Optics GmbH, Munich, Germany.
    Reutlinger, Arnd
    Kampf Telescope Optics GmbH, Munich, Germany.
    Brandão, Ana D.
    European Space Research and Technology Centre, ESTEC, Noordwijk, Netherlands.
    Pambaguian, Laurent
    European Space Research and Technology Centre, ESTEC, Noordwijk, Netherlands.
    Seidel, André
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Lopéz, Elena
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Brückner, Frank
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Beyer, Eckhard
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany; Technische Universität Dresden, Dresden, Germany.
    Leyens, Christoph
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany; Technische Universität Dresden, Dresden, Germany.
    Microstructural, mechanical, and thermo-physical characterization of hypereutectic AlSi40 fabricated by selective laser melting2019Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 31, nr 2, artikel-id 02232Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The powder bed additive manufacturing process selective laser melting (SLM) enables designers and engineers to overcome restrictions of conventional manufacturing technologies. The potential of fabricating complex lightweight structures and processing advanced materials is a key feature for enhancing further development of high performance components for space applications. Due to a high specific stiffness and a thermal expansion coefficient very close to electroless nickel, which is an advantageous optical coating material, the hypereutectic aluminum-silicon alloy AlSi40 shows great potential for the manufacturing of optical mirrors for space applications. In prior investigations, Hilpert et al.showed the feasibility to process AlSi40 by SLM [E. Hilpert and S. Risse, Materials Science & Technology Conference and Exhibition MS&T'15, Columbus, Ohio, 4–8 October 2015(Association for Iron & Steel Technology, Warrendale, PA, 2015) and E. Hilpert, “Struktur und Eigenschaften von additiv gefertigten hypereutektischen Aluminum-Siliciumlegierungen,” in Werkstoffwoche 2017, Dresden, Germany28 September 2017 (Deutsche Gesellschaft für Materialkunde e.V., Berlin, 2017)]. Nevertheless, in order to qualify this material for space applications, the manufacturing process and fabricated samples need to be thoroughly investigated in terms of microstructural, mechanical, as well as thermo-physical characterization. The authors present results of the SLM process development for manufacturing dense AlSi40 samples with a relative density above 99.50%. The effect of various process parameters, such as hatch distance, preheating, and scanning strategy, on the formation of defects was investigated by destructive [e.g., optical microscopy (OM)] and nondestructive (e.g., computed tomography) testing. In addition, the effect of several thermal post-treatments on the AlSi40 microstructure was profoundly analyzed by multiple methods such as OM, scanning electron microscopy, and energy dispersive x-ray spectroscopy analysis. Moreover, mechanical and thermo-physical testing of manufactured specimens was conducted to provide material characteristics for component design. In conclusion, the determined material properties of AlSi40 samples fabricated by SLM were compared to bulk material properties. The gained knowledge and testing data were evaluated in order to identify correlations and dependencies.

  • 43.
    Müller, M.
    et al.
    Fraunhofer IWS, Winterbergstraße 28, Dresden 01277, Germany; Technische Universität Dresden, Helmholtzstr. 7, 01069 Dresden, Germany.
    Labisch, C. C.
    Fraunhofer IWS, Winterbergstraße 28, Dresden 01277, Germany.
    Gerdt, L.
    Fraunhofer IWS, Winterbergstraße 28, Dresden 01277, Germany.
    Bach, L.
    Fraunhofer IWS, Winterbergstraße 28, Dresden 01277, Germany.
    Riede, M.
    Fraunhofer IWS, Winterbergstraße 28, Dresden 01277, Germany.
    Kaspar, J.
    Fraunhofer IWS, Winterbergstraße 28, Dresden 01277, Germany.
    López, Elena
    Fraunhofer IWS, Winterbergstraße 28, Dresden 01277, Germany.
    Brueckner, Frank
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. Fraunhofer IWS, Winterbergstraße 28, Dresden 01277, Germany.
    Zimmermann, M.
    Fraunhofer IWS, Winterbergstraße 28, Dresden 01277, Germany; Technische Universität Dresden, Helmholtzstr. 7, 01069 Dresden, Germany.
    Leyens, C.
    Fraunhofer IWS, Winterbergstraße 28, Dresden 01277, Germany; Technische Universität Dresden, Helmholtzstr. 7, 01069 Dresden, Germany.
    Multimaterial direct energy deposition: From three-dimensionally graded components to rapid alloy development for advanced materials2023Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 35, nr 1, artikel-id 012006Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Laser-based direct energy deposition (L-DED) with blown powder enables the simultaneous or sequential processing of different powder materials within one component and, thus, offers the possibility of additive multimaterial manufacturing. Therefore, the process allows a spatially resolved material allocation and fabrication of sharp or even graded material transitions. Within this contribution, the latest results from two major research fields in multimaterial L-DED—(I) automation and (II) rapid alloy development of high entropy alloys (HEAs) by in situ synthesis—shall be presented. First, an automated multimaterial deposition process was developed, which enables the automated manufacturing of three-dimensionally graded specimens. For this, a characterization of the deposition system regarding powder feeding dynamics and resulting powder mixtures in the process zone was conducted. The obtained system characteristics were used to achieve a three-dimensional deposition of specified powder mixtures. The fabricated specimens were analyzed by energy-dispersive x-ray spectroscopy, scanning electron microscopy, and micro hardness measurement. The research demonstrates the increasing readiness of L-DED for the fabrication of multimaterial components. Second, the latest results from rapid alloy development for HEAs by DED are presented. By the simultaneous usage of up to four powder feeders, a vast range of alloy compositions within the Al–Ti–Co–Cr–Fe–Ni HEA system was investigated. For this, tailored measurement systems such as an in-house developed powder sensor were beneficially used. The study shows the influence of a variation of Al on the phase formation and resulting mechanical properties and demonstrates the potential of L-DED for reducing development times for new alloys.

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  • 44.
    Näsström, Jonas
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Brueckner, Frank
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. Fraunhofer Institute for Material and Beam Technology, IWS, Dresden, Germany.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Laser enhancement of wire arc additive manufacturing2019Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 31, nr 2, artikel-id 022307Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Additive manufacturing (AM) can be used for the fabrication of large metal parts, e.g., aerospace/space applications. Wire arc additivemanufacturing (WAAM) can be a suitable process for this due to its high deposition rates and relatively low equipment and operationcosts. In WAAM, an electrical arc is used as a heat source and the material is supplied in the form of a metal wire. A known disadvantageof the process is the comparably low dimensional accuracy. This is usually compensated by generating larger structures than desired andmachining away excess materials. So far, using combinations of arc in atmospheric conditions with high precision laser heat sources forAM has not yet been widely researched. Properties of the comparable cheap arc-based process, such as melt pool stability and dimensionalaccuracy, can be improved with the addition of a laser source. Within this paper, impacts of adding a laser beam to the WAAMprocess are presented. Differences between having the beam in a leading or a trailing position, relative to the wire and arc, are alsorevealed. Structures generated using the arc-laser-hybrid processes are compared to ones made using only an arc as the heat source. Bothgeometrical and material aspects are studied to determine the influences of laser hybridization, applied techniques including x ray,energy-dispersive X-ray spectroscopy, and high precision 3D scanning. A trailing laser beam is found to best improve topological capabilitiesof WAAM. Having a leading laser beam, on the other hand, is shown to affect cold metal transfer synergy behavior, promotinghigher deposition rates but decreasing topological accuracy.

  • 45.
    Näsström, Jonas
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Frostevarg, Jan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Multipass laser hot-wire welding: Morphology and process robustness2017Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 29, nr 2, artikel-id 022014lArtikel i tidskrift (Refereegranskat)
    Abstract [en]

    There are great prospects for utilizing multipass laser hot-wire welding to join thick steel sheets, especially for techniques commonly performed in single passes, e.g., laser arc hybrid welding, fall short, presenting great opportunities for vehicle industries and offshore applications. Many modern approaches for applying these techniques rely on customized wire feeding nozzles or special scanner optics to ensure proper laser–wire interactions and, in turn, robust process behavior, making them less accessible to many industries. Here, we present a modified adaption of laser hot-wire welding, utilizing more readily available equipment, including an unmodified welding source and a nozzle, presented and evaluated through means of, e.g., high speed imaging and macroscopy. This technique was found to have high process robustness, especially for sealing passes, if wire resistance heating is kept within suitable levels. It is able to both maintain proper laser–wire interaction and produce close to net-shape weld caps. Also, recommended process parameters are presented, together with a description of a potential method for suppressing solidification cracking.

  • 46.
    Ohlsson, L.
    et al.
    Luleå tekniska universitet.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik. Laser Expertise Ltd., Nottingham, England.
    Ivarson, Anders
    Luleå tekniska universitet.
    Magnusson, Claes
    Luleå tekniska universitet.
    Comparison between abrasive water jet cutting and laser cutting1991Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 3, nr 3, s. 46-50Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper is intended to demonstrate the advantages and disadvantages of laser profiling techniques as compared with the Abrasive Water Jet (AWJ). The growth of AWJ as a cutting tool has provided engineers with a new profiling technique which often offers great technical and commercial advantages over more traditional methods. However, AWJ cutting is not the best solution to all profiling problems. There are a number of techniques which compete with or complement the process and the optimum profiling method can be difficult to identify. The following paper serves as a general guide-line comparing two competitive cutting methods (CO2 laser cutting and Nd: YAG laser cutting) with AWJ cutting. The subject of cutting covers a great many more processes than can be reviewed in one article but the techniques to be discussed were chosen because they all involve profiling using an axially symmetric energy beam of some sort

  • 47.
    Olsson, Rickard
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. Laser Nova AB, SE-831 48 Östersund, Sweden.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Frostevarg, Jan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kaplan, Alexander F. H.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Normal vector distribution as a classification tool for convoluted rough surfaces with overhanging features2020Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 32, nr 2, artikel-id 022030Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Convoluted rough surfaces involving overhanging features can be a natural consequence of laser additive manufacturing and other spray techniques or can be generated deliberately by laser surface texturing, e.g., to aid osseointegration. Overhanging features add an extra level of complexity to the topography of a rough surface and can have a substantial effect on wettability, etc. However, features of this type are invisible to traditional surface roughness measurement techniques. This work presents a computer-based surface analysis method that gives useful information about the presence and nature of overhanging features on rough technical surfaces. The technique uses micro-computer tomography to generate a typical cross section of the surface under investigation. The angles of the vectors normal to the surface can then be analyzed to reveal the presence of overhanging features, which can also be indicated by the standard deviation of the normal vector distribution. Titanium surfaces generated by six different techniques were compared. The characteristics of these surfaces varied strongly, as did the shapes of the overhangs involved. These variations are reflected by different statistical distributions of the normal vectors.

  • 48.
    Olsson, Rickard
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. Laser Nova AB.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Palmquist, A.
    Department of Biomaterials, University of Gothenburg.
    Brånemark, R.
    Department of Orthopaedic Surgery, University of California, San Francisco.
    Frostevarg, Jan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    The production of osseointegrating (bone bonding) surfaces on titanium screws by laser melt disruption.2018Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 30, nr 4, artikel-id 042009Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Several techniques can be used to modify implant surfaces in order to accelerate bone growth around titanium implants. One method is to generate a surface structure which stimulates bone growth and remodelling. This paper describes and explains a non-ablative method for producing osseointegrating (structural and functional bone bonding) surfaces on titanium implants using laser processing. The focus is especially on surface texturing of dental implant screws, where the ability of a Nd:YAG laser to generate ‘splashy’ surfaces covered in resolidified micro scale droplets coated with nano-scale surface oxides is assessed. The surfaces produced were analysed by scanning electron microscope (SEM) and energy dispersive x-ray spectroscopy (EDS). It is concluded that laser processing using Q-pulsed Nd:YAG lasers can generate surfaces which match the demands set by clinical experience. One important characteristic of the surfaces discussed here is that they involve overhanging features which are suitable for trapping red blood cells and which cannot be created by mechanical or chemical roughening techniques.

  • 49.
    Olsson, Rickard
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. Laser Nova AB, Östersund, Sweden.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Palmquist, Anders
    Department of Biomaterials, University of Gothenburg, Gothenburg, Sweden.
    Brånemark, Rickard
    Department of Orthopaedic Surgery, University of California, San Francisco, CA, USA.
    Frostevarg, Jan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Formation of osseointegrating (bone integrating) surfaces on titanium by laser irradiation2019Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 31, nr 2, artikel-id 022508Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Pulsed lasers can be used to modify the surface of medical implants in order to accelerate bone growth (osseointegration). A surface covered in attached droplets with diameters between 1 and 20 μm is a beneficial surface for rapid osseointegration. This paper presents the results of an experimental program in which a broad range of laser parameters and different atmospheres were used to create different surface textures on titanium substrates, including the desired "attached droplet" topology. The resulting surfaces were analyzed by scanning electron microscopy and micro-computer tomography. The paper explains how different types of surfaces are created by the laser-material interaction under different conditions and focus characteristics. It is shown that optimization of the laser parameters results in a robust process, which produces a surface that is fundamentally different from those created by nonlaser methods.

  • 50.
    Pocorni, Jetro
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. Laser Expertise Ltd., Acorn Park Industrial Estate.
    Frostevarg, Jan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Investigation of the Piercing Process in Laser Cutting of Stainless Steel2017Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 29, nr 2, artikel-id 022201Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper investigates the laser piercing process which precedes nearly every laser cutting operation. The two most important aspects of the piercing process are: a) How long does it take to pierce the material? And b) How wide is the pierced hole? If the hole is no wider than the cut line, the material can be pierced on the line to be cut. In this paper 10 mm thick stainless steel was pierced by a multikilowatt fibre laser to compare efficiency and quality when piercing with a continuous wave (cw) output and a selected range of power modulation parameters. The different processes were observed by high speed imaging and subsequently examined by visual observation. High speed imaging is used to time the penetration event and to study the laser-material interactions involved in drilling the pierced holes. The results show that appropriate laser power modulation settings can considerably reduce both the piercing time and the required energy to generate any piercing hole required for the subsequent cutting process. This pulse-pierce technique and the differences between piercing with a continuous and a power modulated laser beam are further explained and discussed. Also the effect on the size of the entrance to the pierced hole depending on power modulation regimes was investigated in this paper.

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