Dr.-Ing.

Day, Robin

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Compensation of structure distortion in nonisothermalhot forming of laser structured thin glass

2024-06-12 , Kohse, Martin , Meiners, Constantin , Plakhotnik, Denys , Vogel, Paul-Alexander , Day, Robin , Grunwald, Tim , Bergs, Thomas

The modern automotive industry employs various complex shaped glass components. Around 50% of these components are currently functionalized using environmentally and economically unfriendly etching or replication processes. We present a new approach of direct laser structuring on glass, which reduces costs and energy by up to 60% and avoids harmful chemicals, offering a more sustainable alternative to conventional processes.

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Initial experiments to regenerate the surface of plasma-facing components by wire-based laser metal deposition

2024 , Tweer, Jannik , Day, Robin , Derra, Thomas , Dorow-Gerspach, Daniel , Loewenhoff, Thorsten , Wirtz, Marius , Linsmeier, Christian , Bergs, Thomas , 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.

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Benchmark of Abrasives for Different Applications

2022 , Schüler, Manuel , Day, Robin , Bergs, Thomas

The industrial use of abrasive waterjet (AWJ) technology has its strength in the machining of conventionally difficult-to-machine materials where the use of abrasives is obligatory. Since the use of AWJ technology, garnet abrasive has become the standard due to its performance and availability. Facing the impending shortage of natural raw materials, rising prices, and increasing environmental requirements, users of waterjet technology must optimize their processes. A wide range of individual machining tasks and materials to be processed holds great potential for tailoring the consumption of valuable resources and costs in the future. A fundamental comparison of different abrasive grit is made to contribute to the efficient use of solids for dedicated applications and to identify resource-efficient alternatives. For this purpose, an overview is given of the abrasive performance in AWJ machining. The experiments will be examined for both AWJ cutting through (CT) and controlled-depth machining (CDM) or AWJ milling techniques on two heat-treated modifications of a 42CrMo4 steel alloy. Finally, a fundamental discussion of grit properties on the systematic change of size distribution serves as a basis to meet the requirements of reusability and their attractiveness for future waterjet production.

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Improving position accuracy in large-scale laser structuring processes using surface feature detection algorithms

2022 , Kohse, Martin , Hauffe-Waschbüsch, Tobias , Day, Robin , Bergs, Thomas

Laser structuring is an effective way to functionalize or texture components. For the machining of large components > 500 x 500 mm, precision machine tools costing up to €1.5 mio are needed. This circumstance leads to a limited market applicability. Fraunhofer IPT is developing a cost-efficient laser structuring solution making it possible to scale up maximum processing area by mounting the laser structuring head on an industrial robot. However, high positioning accuracy of < 5 µm is needed for laser structuring while an industrial robot system delivers a maximum position repeatability of about 70 µm. Fraunhofer IPT has developed a compensation strategy using an inline camera setup. The system detects reference features of markers and texture by using FAST algorithm for corner detection with a laplacian image pyramid. The current system is capable to set exposure times automatically and to compensate position inaccuracies of up to 1 mm to an overall accuracy of < 5 µm despite a camera chip resolution of 5.3 µm/px. In this contribution we present an overview of the compensation algorithm with an evaluation method for process stabilization and identify challenges, e.g. illumination and material properties will be addressed.

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Assessing the Environmental and Economic Impact of Wire-Arc Additive Manufacturing

2024-05 , Derra, Thomas , Belghith, Khouloud , Gräfe, Stefan , Day, Robin , Bergs, Thomas

Additive Manufacturing (AM) has continuously been integrated in the modern production landscape and complements traditional manufacturing processes by allowing the creation of complex three-dimensional objects through layer-by-layer material deposition. Especially with new design opportunities and short lead times it has significant impact on different industrial sectors such as healthcare, automotive and aerospace. Compared to other AM technologies, Wire Arc Additive Manufacturing (WAAM) has a particularly high material deposition rate and a high degree of flexibility when building large components. Therefore, WAAM has great potential for efficient and resilient production. To quantify this potential the environmental and economic impact must be assessed. The presented study focuses Life Cycle Assessment (LCA) and Life Cycle Costing (LCC) and presents a general methodology for impact analysis as well as a transfer to WAAM. The methodology consists of four steps in accordance with ISO 14044:2006: goal and scope definition, inventory analysis (environmental/economic), environmental impact assessment/cost aggregation, interpretation. For the transfer to WAAM a cradle-to-gate analysis is conducted. The relevant process chain leads from alloy production to the WAAM product manufacturing. The methodology generates relative data, so the final assessment of WAAM must be set into context with alternative processes.

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Influence on the Bead Geometry in Laser Metal Deposition with Wire

2023-09-28 , Weidemann, Tizia , Abuabiah, Mohammad , Shaqour, Bahaa , Day, Robin , Bergs, Thomas , Plapper, Peter

Laser metal deposition with wire (LMD-w) is a promising additive manufacturing technology, which attracts interest due to the low waste of material, the flexible application possibilities along the production chain and the improved metallurgical properties compared to powder-based processes. However, the complex handling of the technology and the resulting low process stability inhibit the broad industrial application. In particular, the varying bead geometry prevents automation and series production. To improve the geometric accuracy, it is necessary to understand influencing parameters. For this purpose, a parameter study is carried out in the present work. Different combinations of laser power, wire feed rate, traverse speed and welding angle are set, and the deposited beads are evaluated in terms of height and width. A factorial design experiment with the Box-Behnken was used to analyse and understand the interaction of these parameters on the deposited beads.

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Process stabilization through pulsed laser-induced melt pool shaping in dual-beam LMD

2022 , Gipperich, Marius , Gräfe, Stefan , Day, Robin , Bergs, Thomas

Laser Metal Deposition (LMD) is an additive manufacturing process that reaches high deposition rates. Its applications are mainly found in repair, cladding and manufacturing. The two commonly used LMD processes are powder-based (LMD-p) and wire-based (LMD-w). Despite the fact that wire-based LMD uses material more efficiently, its process stability is a major concern. One approach to increase the process stability is superposing a pulsed laser (pw) beam with the conventionally used continuous laser (cw). Previous studies have shown that the metal vapor caused by pulsed laser-induced evaporation in the process zone significantly improves energy absorption. Furthermore, a direct relation between vapor pressure and melt pool form has been demonstrated. In this contribution, we correlate the pw-controlled melt pool geometry to process stability. High-speed camera imaging is employed to evaluate the dynamic melt pool behavior as a function of pw frequency and power. It is shown that irregular melt pool oscillations impairing process stability in conventional LMD-w are reduced if the pulsed laser is added. The melt front is shaped depending on the acting pw-induced pressure. This leads to a more stable interaction between wire and melt pool. Furthermore, the pw pressure changes the welding bead height and width. This cross-sectional geometry has an impact on the resulting waviness in 3D build-up. We also investigate how the waviness influences process stability during multilayer LMD-w. The results demonstrate that the dual beam technology is a promising way to develop more reliable and resource-efficient AM processes.

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Assessing the Environmental and Economic Impact of Wire Arc Additive Manufacturing

2024-04-25 , Derra, Thomas , Belghith, Khouloud , Gräfe, Stefan , Day, Robin , Bergs, Thomas

Additive Manufacturing (AM) has continuously been integrated in the modern production landscape and complements traditional manufacturing processes by allowing the creation of complex three-dimensional objects through layer-by-layer material deposition. Especially with new design opportunities and short lead times it has significant impact on different industrial sectors such as healthcare, automotive and aerospace. Compared to other AM technologies, Wire Arc Additive Manufacturing (WAAM) has a particularly high material deposition rate and a high degree of flexibility when building large components. Therefore, WAAM has great potential for efficient and resilient production. To quantify this potential the environmental and economic impact must be assessed. The presented study focuses Life Cycle Assessment (LCA) and Life Cycle Costing (LCC) and presents a general methodology for impact analysis as well as a transfer to WAAM. The methodology consists of four steps in accordance with ISO 14044:2006: goal and scope definition, inventory analysis (environmental/economic), environmental impact assessment/cost aggregation, interpretation. For the transfer to WAAM a cradle-to-gate analysis is conducted. The relevant process chain leads from alloy production to the WAAM product manufacturing. The methodology generates relative data, so the final assessment of WAAM must be set into context with alternative processes.

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Emissionsminderung beim Laserauftragschweißen

2022 , Gräfe, Stefan , Paulus, Rebecca , Wohter, Daniel , 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.

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Einfluss des Laserstrahldurchmessers auf das Bearbeitungsergebnis beim Laser Powder Bed Fusion

2022 , Day, Robin Johannes , Schleifenbaum, Johannes Henrich , Bergs, Thomas

Die vorliegende Arbeit erforscht die Anlagenübertragbarkeit von LPBF-Anlagen als Schlüssel zum größeren industriellen Einsatz des ökologischen und ökonomischen Fertigungsverfahrens. Aufgrund der Komplexität des Themas wird nur der Teilaspekt des Einflusses des Bearbeitungswerkzeuges auf das Bearbeitungsergebnis fokussiert. Ziel der Untersuchung ist der Anlagenübertrag des Bearbeitungsergebnisses zwischen Anlagen mit einer maximalen Abweichung des Bearbeitungsstrahldurchmessers zwischen 34 μm und 100 μm. Dies umfasst nahezu alle aktuell kommerziell verfügbaren LPBF-Anlagensysteme. Ergebnis ist, dass der Übertrag für alle aktuell industriell verfügbaren Fokusstrahldurchmesser von 34 - 100 μm gelingt. Dabei werden drei verschiedene Methodiken zum Übertrag betrachtet. Die erste Methodik findet Anwendung bei Abweichung des Bearbeitungsstrahldurchmessers kleiner 15 %. In diesen Fällen wurde die normierte Enthalpie oder die Intensität Umrechnung als zielführend identifiziert. Werden die Abweichungen größer, scheitert diese Methodik. In diesem Fall ist eine Betrachtung des Umschmelzregimes sinnvoll. Mithilfe des Breiten- zu Tiefenverhältnisses wird das Übergangsschweißregime reproduziert. Im dritten Fall wird mit Defokussierung gearbeitet. Dabei kann der kleinste Fokusstrahldurchmesser auf den doppelten Durchmesser defokussiert werden. So wird weiterhin mit ein und demselben Bearbeitungsstrahldurchmesser bearbeitet und die Bearbeitungsergebnisse werden bei guter Strahlqualität vergleichbar. In den Untersuchungen war eine Fokusverschiebung oberhalb der Pulverbettebene zielführend. Die Anlagenübertragbarkeit ist bei Beachtung der Bedeutung des Bearbeitungswerkzeuges möglich und trägt so zur Skalierbarkeit des LPBF Verfahrens bei. Durch ihre ökologisch hocheffizienten Eigenschaften und die ökonomischen Vorteile der Skalierung trägt die Arbeit einen Beitrag zur Reduktion des industriellen Ressourcenverbrauchs bei. Davon wiederum profitieren Umwelt, Klima und zukünftige Generationen.

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