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PublicationProcess Setup and Boundaries of Wire Electron Beam Additive Manufacturing of High-Strength Aluminum Bronze( 2023-08-08)In recent years, in addition to the commonly known wire-based processes of Directed Energy Deposition using lasers, a process variant using the electron beam has also developed to industrial market maturity. The process variant offers particular potential for processing highly conductive, reflective or oxidation-prone materials. However, for industrial usage, there is a lack of comprehensive data on performance, limitations and possible applications. The present study bridges the gap using the example of the high-strength aluminum bronze CuAl8Ni6. Multi-stage test welds are used to determine the limitations of the process and to draw conclusions about the suitability of the parameters for additive manufacturing. For this purpose, optimal ranges for energy input, possible welding speeds and the scalability of the process were investigated. Finally, additive test specimens in the form of cylinders and walls are produced, and the hardness profile, microstructure and mechanical properties are investigated. It is found that the material CuAl8Ni6 can be well processed using wire electron beam additive manufacturing. The microstructure is similar to a cast structure, the hardness profile over the height of the specimens is constant, and the tensile strength and elongation at fracture values achieved the specification of the raw material.
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PublicationStudie zur Stärkung der Holzbauwirtschaft in der Metropolregion Berlin-Brandenburg(Fraunhofer IPK, 2023)Berlin verfolgt das Ziel, sich bis zum Jahr 2050 zu einer klimaneutralen Stadt zu entwickeln: Im Vergleich zur Gesamtsumme der CO2-Emissionen des Jahres 1990, sollen diese bis 2030 um mindestens 60 Prozent und bis zum Jahr 2050 um mindestens 85 Prozent verringert werden. Fast ein Drittel der CO2-Emissionen in Deutschland kann dem Gebäudebereich zugerechnet werden. Einen enormen Hebel zur Verbesserung der Klimabilanz bietet der konsequente Einsatz von Baumaterialien auf Basis nachwachsender Rohstoffe. Insbesondere der Baustoff Holz kann für die Metropolregion Berlin-Brandenburg eine zentrale Stellung zur Erreichung der Klimaziele einnehmen. Hierzu wurde bereits im Frühjahr 2021, in der Vorhabensliste1 des Strategischen Gesamtrahmens Hauptstadtregion, eine regionale Holzbau-Offensive festgehalten. Diese hat zum Ziel, die Region Berlin-Brandenburg zu einer Region des Holzbaus zu entwickeln. Damit die holzbasierte Transformation des Bauens in der Hauptstadtregion nachhaltig gelingt, ist insbesondere eine starke kreislaufwirtschaftsbasierte regionale Holzbauwirtschaft von Bedeutung.
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PublicationA life cycle assessment of joining processes in the automotive industry, illustrated by the example of an EV battery case( 2023)
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PublicationResource efficient production of car body parts - implementation of digital twins across process chains( 2022-09-21)
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PublicationResult quality evaluation of Directed Energy Deposition Additive Manufacturing simulations with progressive simplification of transient heat-source motion( 2022-09-05)
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PublicationInvestigation of liquid metal embrittlement avoidance strategies for dual phase steels via electro-thermomechanical finite element simulation( 2022-06)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.
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PublicationIntegrated weld preparation designs for the joining of L-PBF and conventional components via TIG welding( 2022-04-18)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.
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PublicationQuality Prediction in Directed Energy Deposition Using Artificial Neural Networks Based on Process Signals( 2022-04-14)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.
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PublicationLearning Demonstrator for Anomaly Detection in Distributed Energy Generation( 2022-04-07)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.
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PublicationMethodik zur modellbasierten Systemarchitekturdefinition von Smart-circular Product-Service Systems(Fraunhofer Verlag, 2022)Induziert durch Digitalisierung und Servitisierung bieten Unternehmen in zunehmendem Maße Systeme aus vernetzten mechatronischen Produkten, Software und Dienstleistungen an: sogenannte Smart-circular Product Service Systems (Smart-circular PSS). Ungeklärt ist bislang, wie Teams bei der Entwicklung von Smart-circular PSS sachgerecht methodisch unterstützt werden können. Diese Arbeit begegnet diesen Beobachtungen mit der Forschungshypothese, dass sich Systemarchitekturen von Smart-circular PSS durch geeignete Methoden des Modellbasierten Systems Engineerings (MBSE) so entwerfen lassen, dass die Systeme effektiv und effizient zu einer CE beitragen. Aufbauend auf gewonnenen Erkenntnissen wurde die Methodik zur Definition von Smart-circular PSS-Systemarchitekturen (MESSIAH) entwickelt, die Entwicklungsteams bei der Konzeptionierung von Smart-circular PSS unterstützt. Die Methode beinhaltet eine Modellierungsgenerik, eine gerichtete Methode sowie einen Baukasten zum schnellen Prototypisieren von Services. MESSIAH wurde anhand von fünf Studien evaluiert und erprobt.
