Now showing 1 - 10 of 6253
  • Publication
    Result quality evaluation of Directed Energy Deposition Additive Manufacturing simulations with progressive simplification of transient heat-source motion
    ( 2022-09-05) ;
    Elsner, Beatrix A.M.
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    Neubauer, Ingo
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    Directed Energy Deposition (DED) additive manufacturing has recently been adopted in the industry for the build-up of structural components with weld lengths up to kilometers. As with all welding processes, DED suffers from thermal distortion, causing loss of dimensional accuracy and risk of cracking. Currently, process optimization with objective to minimize distortion requires expensive experimental trial-and-error. With numerical simulation of the DED process, this distortion compensation can be performed virtually, significantly reducing experimental trials. Although such approaches are generally available, their widespread adoption is currently being hampered by long computational times for large builds. This work presents a novel approach to reduce the calculation time by a simplification of the transient heat-source motion. This approach is assessed in terms of result accuracy for an industrial-scale component by progressively reducing the resolution of the heat-source motion. Calculation times as well as distortions in comparison to experimental trials are investigated.
  • Publication
    Laserstrahlhybridschweißen von Türmen für Windkraftanlagen
    ( 2022-08-29)
    Üstündag, Ömer
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    Bakir, Nasim
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    Knöfel, Frieder
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    Das Laserstrahlhybridschweißen ist beim Schweißen von Türmen für Windkraftanlagen eine Alternative zum Unterpulverschweißen von Dickblechen in Mehrlagentechnik und bietet hier ökonomische und ökologische Vorteile. Der industrielle Einsatz des Verfahrens ist jedoch durch prozessspezifische Herausforderungen eingeschränkt. Die im Beitrag beschriebene kontaktlose elektromagnetische Badstütze dient zur Erweiterung des Verfahrenspotenzials im Dickblechbereich >15 mm.
  • Publication
    Investigation of liquid metal embrittlement avoidance strategies for dual phase steels via electro-thermomechanical finite element simulation
    ( 2022-06) ;
    Böhne, Christoph
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    Meschut, Gerson
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    Modern advanced high-strength steel (AHSS) sheets used in automotive body construction are mostly zinc coated for corrosion resistance. The presence of zinc can cause cracking in steels due to liquid metal embrittlement (LME) during resistance spot welding (RSW). In combination with factors such as tensile strains, liquid zinc can lead to the formation of brittle, intergranular cracks in the weld and heat affected zone. While practical investigations to mitigate LME occurrence exist, the reason why a certain parameter might cause or prevent LME is often unknown. Numerical resistance spot welding simulation can visualize the underlying stresses, strains and temperatures during the welding process and investigate experimentally unmeasurable phenomena. In this work, a 3-dimensional electro-thermomechanical finite element approach is used to assess and investigate the critical parameters leading to LME occurrence. Experimentally observed crack sizes are correlated with the corresponding local strain rates and temperature exposure durations in the simulation. With this data, a map of LME occurrence over driving influence factors is drafted and discussed for effectiveness.
  • Publication
    Integrated weld preparation designs for the joining of L-PBF and conventional components via TIG welding
    ( 2022-04-18)
    Geisen, Ole
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    Graf, Benjamin
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    Laser powder bed fusion (L-PBF) of entire assemblies is not typically practical for technical and economic reasons. The build size limitations and high production costs of L-PBF make it competitive for smaller, highly complex components, while the less complex elements of an assembly are manufactured conventionally. This leads to scenarios that use L-PBF only where it's beneficial, and it require an integration and joining to form the final product. For example, L-PBF combustion swirlers are welded onto cast parts to produce combustion systems for stationary gas turbines. Today, the welding process requires complex welding fixtures and tack welds to ensure the correct alignment and positioning of the parts for repeatable weld results. In this paper, L-PBF and milled weld preparations are presented as a way to simplify the Tungsten inert gas (TIG) welding of rotationally symmetrical geometries using integrated features for alignment and fixation. Pipe specimens with the proposed designs are manufactured in Inconel 625 using L-PBF and milling. The pipe assembly is tested and TIG welding is performed for validation. 3D scans of the pipes before and after welding are evaluated, and the weld quality is examined via metallography and computed tomography (CT) scans. All welds produced in this study passed the highest evaluation group B according to DIN 5817. Thanks to good component alignment, safe handling, and a stable welding process, the developed designs eliminate the need for part-specific fixtures, simplify the process chain, and increase the process reliability. The results are applicable to a wide range of components with similar requirements.
  • Publication
    Quality Prediction in Directed Energy Deposition Using Artificial Neural Networks Based on Process Signals
    ( 2022-04-14)
    Marko, Angelina
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    Bähring, Stefan
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    Raute, Maximilian Julius
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    The Directed Energy Deposition process is used in a wide range of applications including the repair, coating or modification of existing structures and the additive manufacturing of individual parts. As the process is frequently applied in the aerospace industry, the requirements for quality assurance are extremely high. Therefore, more and more sensor systems are being implemented for process monitoring. To evaluate the generated data, suitable methods must be developed. A solution, in this context, was the application of artificial neural networks (ANNs). This article demonstrates how measurement data can be used as input data for ANNs. The measurement data were generated using a pyrometer, an emission spectrometer, a camera (Charge-Coupled Device) and a laser scanner. First, a concept for the extraction of relevant features from dynamic measurement data series was presented. The developed method was then applied to generate a data set for the quality prediction of various geometries, including weld beads, coatings and cubes. The results were compared to ANNs trained with process parameters such as laser power, scan speed and powder mass flow. It was shown that the use of measurement data provides additional value. Neural networks trained with measurement data achieve significantly higher prediction accuracy, especially for more complex geometries.
  • Publication
    Learning Demonstrator for Anomaly Detection in Distributed Energy Generation
    ( 2022-04-07)
    Pelchen, Timo
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    Thiele, Gregor
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    Radke, Marcel
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    Schade, David
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    Machine learning based anomaly detection methods on process data can be used to secure critical infrastructure. The design and installation of these methods require detailed understanding of both the facilities and the machine learning methods. Therefore, they are mostly incomprehensible for non-experts and thus acting as a barrier hindering the fast spread of such technologies. This article presents the systematic development of a demonstrator which enables presentations of anomaly detection on the example of a simulated wind farm. The specially designed user-interface allows a comprehensive experience. This article documents the use of the demonstrator for experts experienced in energy systems which are interested in the application of machine learning algorithms.
  • Publication
    Material-adapted and process-reliable multi-wire submerged arc welding of large-diameter pipes
    ( 2022-03-07) ; ; ; ;
    Lichtenthäler, Frank
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    Stark, Michael
    Ensuring the required mechanical-technological properties of welds is a critical issue in the application of multi-wire submerged arc welding processes in the manufacture of largediameter pipes made of high-strength fine-grained steels of grade X70 and higher according to API 5L. Excessive heat input of up to 10 kJ/mm is one of the main causes of the formation of microstructural areas in the heat-affected zone with deteriorated mechanical properties, such as impact toughness and tensile strength. In this work, a variant of a five-wire submerged arc welding process is proposed that reduces the weld volume and the heat input, while retaining the high process stability and production speed of multi-wire submerged arc welding. By adapting the welding wire configuration of a five-wire submerged arc welding process and the energetic parameters of the arcs, the high penetration depth of approx. 24 mm and a 10 % reduction in the weld cross-section could be achieved compared to the usual process configuration. This effect was transformed into a higher welding speed, which led to a reduction in the heat input. A concept for process monitoring is proposed in order to maintain constant manufacturing quality in large-diameter pipe production. In addition to the analysis of electrical process signals such as welding current and welding voltage, acoustic process monitoring using vibro-acoustic sensors provides reliable information on the stability of the welding process.
  • Publication
    Study on the transition behavior of the bulging effect during deep penetration laser beam welding
    ( 2022)
    Artinov, A.
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    Meng, X.
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    Bachmann, M.
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    Rethmeier, M.
    The present work is devoted to the study of the transition behavior of the recently confirmed widening of the weld pool, known as the bulging effect, during high-power deep penetration laser beam welding of thick unalloyed steel sheets. A three-dimensional transient multi-physics numerical model is developed, allowing for the prediction of the bulge formation and the study of its temporal behavior. The model is generalized to account automatically for the transition from partial to complete penetration. Several experimental measurements and observations, such as drilling period, weld pool length, temperature, efficiency, and metallographic cross-sections are used to verify the model and assure the plausibility of the numerical results. The analysis of the calculated temperature and velocity distributions, as well as the evolution of the keyhole geometry, show that the formation of a bulging region strongly depends on the penetration depth of the weld. Based on the numerical results, the bulge is found to occur transiently, having its transition from a slight bulge to a fully developed bulging between penetration depths of 6 mm and 9 mm, respectively.
  • Publication
    Hybrid laser-arc welding of laser- and plasma-cut 20-mm-thick structural steels
    ( 2022)
    Üstündag, Ömer
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    Bakir, Nasim
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    It is already known that the laser beam welding (LBW) or hybrid laser-arc welding (HLAW) processes are sensitive to manufacturing tolerances such as gaps and misalignment of the edges, especially at welding of thick-walled steels due to its narrow beam diameter. Therefore, the joining parts preferably have to be milled. The study deals with the influence of the edge quality, the gap and the misalignment of edges on the weld seam quality of hybrid laser-arc welded 20-mm-thick structural steel plates which were prepared by laser and plasma cutting. Single-pass welds were conducted in butt joint configuration. An AC magnet was used as a contactless backing. It was positioned under the workpiece during the welding process to prevent sagging. The profile of the edges and the gap between the workpieces were measured before welding by a profile scanner or a digital camera, respectively. With a laser beam power of just 13.7 kW, the single-pass welds could be performed. A gap bridgeability up to 1 mm at laser-cut and 2 mm at plasma-cut samples could be reached respectively. Furthermore, a misalignment of the edges up to 2 mm could be welded in a single pass. The new findings may eliminate the need for cost and time-consuming preparation of the edges.