Dr.-Ing.

Day, Robin

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  • Publication
    Initial experiments to regenerate the surface of plasma-facing components by wire-based laser metal deposition
    ( 2024)
    Tweer, Jannik
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    Day, Robin
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    Derra, Thomas orcid-logo
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    Dorow-Gerspach, Daniel
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    Loewenhoff, Thorsten
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    Wirtz, Marius
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    Linsmeier, Christian
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    Bergs, Thomas
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    Natour, Ghaleb
    Plasma-facing components (PFC) in nuclear fusion reactors are exposed to demanding conditions during operation. The combination of thermal loads, plasma exposure as well as neutron induced damage and activation limits the number of materials suitable for this application. Due to its properties, tungsten (W) is foreseen as plasma-facing material (PFM) for the future DEMOnstration power plant. It is considered suitable due to its exceptionally high melting point, excellent thermal conductivity, low tritium retention and low erosion resistance during plasma exposure. But even tungsten armored PFCs have a limited lifetime due to, among other factors, surface erosion and the resulting thickness reduction of the armor material. In-situ local deposition of tungsten by means of additive manufacturing (AM) could counteract surface erosion and thus increase the service life span of PFCs. After evaluation of the potential AM processes qualified for this task, the wire-based laser metal deposition (LMD-w) process was selected as the most suitable process. First trials were conducted to examine if it is possible to reliably deposit tungsten onto tungsten substrate using the LMD-w process. In these first studies, single welding beads were generated, and in later experiments, entire layers were created from several welding beads which are arranged next to each other. To ensure reproducibility of the results, the substrate temperature was kept constant. Further experiments aimed at the elimination or minimization of problems such as oxidation, occurrence of balling defects, porosity, cracking, surface waviness and insufficient connection to the substrate. To increase the welding bead quality, the input parameters like laser power, deposition velocity, wire feed rate, inert gas flow, as well as the wire position were optimized. Furthermore, stacking of several layers, as well as the remelting of an already created layer, were carried out and investigated. This study represents the first steps in testing the feasibility of an in-situ surface regeneration concept for PFCs.
  • Publication
    Emissionsminderung beim Laserauftragschweißen
    ( 2022)
    Gräfe, Stefan
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    Paulus, Rebecca
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    Wohter, Daniel
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    Day, Robin
    ;
    Bergs, Thomas
    Wire-based laser metal deposition (LMD-w) releases welding fume particles that are harmful to health and the environment. The potential hazard depends on the chemical composition as well as particle number and size. Using a statistical design of experiments, the emissions are characterized and the depen-dence on relevant process factors is determined. From this, process-intrinsic measures for emission reduction are derived.
  • Publication
    Express Wire Coil Cladding as an Advanced Technology to Accelerate Additive Manufacturing and Coating
    ( 2022)
    Gipperich, Marius
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    Riepe, Jan
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    Day, Robin
    ;
    Bergs, Thomas
    Metal shafts are indispensable components in mobility, energy and mechanical engineering. In such applications, the shafts need to withstand severe mechanical loads, friction, high temperature or corrosive media. This is why shafts are often completely made of high-performance alloys. From a technical point of view, coating an inexpensive base shaft with a thin layer of high-performance material is mostly sufficient to ensure its functionality. Adding functional parts such as bearing seats by Additive Manufacturing (AM) is an advantageous approach to increase flexibility and material efficiency. Reliable and economic AM processes need to be developed further, and laser-based processes such as wire-based Laser Metal Deposition (LMD-w) offer high potential to accomplish this. Due to their low deposition rate, however, LMD processes are not economically competitive with high-speed subtractive technologies. Motivated by this challenge, we present an alternative approach for laser-based shaft cladding. Instead of adding the filler wire continuously, wire coils are wound and preplaced on the shaft. In a second step, laser processing while rotating the part generates a metallurgical bond between the wire and the substrate. In this study, several solid and flux-cored wires were analyzed regarding their suitability for this two-step coil winding and LMD process. The resulting surface state and the welded joint quality are evaulated. Metallographic cross sections show low porosity and small heat-affected zones. Thanks to its good scalability, this innovative process can help strongly increase the build-up rate compared to classic LMD-w.