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PublicationFeasibility study of joining of carbon fibre-reinforced polymer composites and aluminium alloys by electron beam welding for use in lightweight construction( 2023-05-12)In recent years, new solutions to reduce the weight of components used in the automotive, railway, and aircraft industries have been researched. Carbon Fibre Composites (CFC) have been used to replace metals in products requiring lightweight construction, such as aircraft or high-performance vehicles due to their exceptional mechanical strength. However, the use of CFCs is limited by the reason of their poor thermal conductivity, particularly on components requiring effective dissipation of power losses. To respond to the requirements, the idea of the material combination of metals and polymer-based composites is proposed. In this study, electron beam welding is used for the joining of aluminium alloys and polymer-based composites. Within the experiments, the relevant process parameters such as beam current, welding speed, and heat input have been optimized to achieve the welding of the aluminium alloys. Then, the joining of aluminium alloys and carbon fibre-reinforced polymer composites has been investigated through the optimized welding process parameters for aluminium alloys. Conclusions are drawn regarding the carbon-fibre reinforced polymer composites (PA6-CF) and aluminium alloys (AlMg3) being joinable through electron beams.
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PublicationMechanical properties of laser welded joints of wrought and heat-treated PBF-LB/M Inconel 718 parts depending on build direction( 2023)Laser-based Powder Bed Fusion of Metal (PBF-LB/M) is a broadly used metal additive manufacturing (AM) method for fabricating complex metallic parts, whose sizes are however limited by the build envelope of PBF-LB/M machines. Laser welding arises as a valid joining method for effectively integrating these AM parts into larger assemblies. PBF-LB/M components must usually be stress-relieved before they can be separated from the build plate. An additional heat treatment can be beneficial for obtaining homogeneous mechanical properties across the seam or for the formation of desired precipitations in nickel-based-alloys. Therefore, the tensile performance of laser welded hybrid (AM/wrought) and AM-AM tensile samples of Inconel 718 is examined after undergoing three different heat treatments and considering three relevant build directions. It can be shown that the build orientation is an influencing factor on weld properties even after two applied heat treatments.
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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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PublicationAnalysis and recycling of bronze grinding waste to produce maritime components using directed energy deposition( 2021)Additive manufacturing promises a high potential for the maritime sector. Directed Energy Deposition (DED) in particular offers the opportunity to produce large-volume maritime components like propeller hubs or blades without the need of a costly casting process. The post processing of such components usually generates a large amount of aluminum bronze grinding waste. The aim of the presented project is to develop a sustainable circular AM process chain for maritime components by recycling aluminum bronze grinding waste to be used as raw material to manufacture ship propellers with a laser-powder DED process. In the present paper, grinding waste is investigated using a dynamic image analysis system and compared to commercial DED powder. To be able to compare the material quality and to verify DED process parameters, semi-academic sample geometries are manufactured.
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PublicationAutomated tool-path generation for rapid manufacturing and numerical simulation of additive manufacturing LMD geometries( 2019)In additive manufacturing (AM) Laser Metal Deposition (LMD), parts are built by welding layers of powder feedstock onto a substrate. Applications for steel powders include forging tools and structural components for various industries. For large parts, the choice of tool-paths influences the build-rate, the part performance and the distortions in a highly geometry-dependent manner. With weld-path lengths in the range of hundreds of meters, a reliable, automated tool path generation is essential for the usability of LMD processes. In this contribution, automated tool-path generation approaches are shown and their results are discussed for arbitrary geometries. The investigated path strategies are the classical approaches: ""Zig-zag-"" and ""contour-parallel-strategies"". After generation, the tool-paths are automatically formatted into g-code for experimental build-up and ASCII for a numerical simulation model. Finally, the tool paths are discussed in regards to volume-fill, microstructure and porosity for the experimental samples. This work presents a part of the IGF project 18737N ""Welding distortion simulation"" (FOSTA P1140)
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PublicationPrognose der Oberflächenbeschaffenheit für die additive Fertigung mittels Laser-Pulver-Auftragschweißen( 2018)In den letzten Jahren hat vor allem die Nachfrage nach additiven Fertigungstechnologien und Reparaturverfahren für hochfeste Werkstoffe einen starken Aufschwung erlebt. Ein Verfahren, welches sich neben der Herstellung von Beschichtungen besonders für diese Anwendungen eignet, ist das Laser-Pulver-Auftragschweißen. Es wird besonders für Reparaturen bzw. zur Herstellung von teuren Bauteilen, wie Werkzeugen oder Turbinenteilen, eingesetzt. Da diese Teile oft großen mechanischen sowie thermischen Belastungen ausgesetzt sind, ist es besonders wichtig, dass die erzeugte Struktur eine hohe Qualität aufweist. In dieser Arbeit wird die statistische Versuchsplanung genutzt, um Modelle für die Oberflächenbeschaffenheiten von Inconel 718 zu generieren. Als Grundlage dient hierbei ein zentral zusammengesetzter Versuchsplan mit großem Parameterfenster. So wird die Leistung zwischen 550 Watt und 1950 Watt, der Vorschub von 530 mm/min bis 920 mm/min, der Pulvermassenstrom von 3 g/min bis 12 g/min sowie der Spotdurchmesser von 1 mm bis 2 mm variiert. Auf diese Weise wird die Spurgeometrie beeinflusst. Darüber hinaus wird das Überlappungsverhältnis zwischen 20% bis 50 % verändert. Die Auswertung der Oberflächenbeschaffenheit erfolgt mit dem auf der Fokusvariation basierendem Oberflächenmessgerät Alicona Infinite- Focus. Dieses Verfahren der 3D Mikrokoordinatenmesstechnik gewährleistet eine zuverlässige Auswertung der Spurgeometrie, der Welligkeit sowie die Messung der mittleren arithmetischen Höhe Sa zur Bestimmung der Oberflächenrauheit. Anschließend werden die generierten Modelle verifiziert. Ziel dabei ist es, kostenintensive Vorversuche in Zukunft einzusparen. Darüber hinaus wird das Prozessverständnis erweitert und signifikante Einflussfaktoren identifiziert.
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PublicationLaser-GMA-hybrid welding of longitudinally welded large-diameter pipes of grades API-X80/X100 to increase the toughness and the production efficiency( 2015)The aim of the present work is to investigate the possibilities of the hybrid laser arc welding regarding the reliable and cost effective production of longitudinal welds on the high strength pipeline steels X80 and X120 and to evaluate the achievable mechanical properties of the laser hybrid welds. The study focused on the investigations of the weld seam toughness in the low temperature range (-60 °C and -40 °C). Suitable filler materials have been identified in the context of this task. It could be shown that the metal powder filler wires, micro alloyed with Ni and partly with Cr and Mo, guaranteed sufficient Charpy impact toughness at low temperature for the both investigated materials (average value 190J for X80 at -60 °C and 53 J for X120 at -40 °C). The modern arc technologies such as modified pulsed spray arc have been used to promote the deeper penetration of the filler material in the narrow laser weld. The edge preparation with a root face of 14 mm has been proposed as optimum, because no penetration of the filler material could be detected over this depth limit and therefor any metallurgical influences on the properties of the weld metal through the welding wire are not possible.
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PublicationLaser and hybrid laser-arc welding of cryogenic 9%Ni steel for construction of LNG storage tanks( 2015)Heat treated 9%Ni steel is considered the most suitable and economic material for construction of large-size Liquefied Natural Gas (LNG) storage tanks which operate at cryogenic temperatures (-196°C). Strength above 700 MPa as well as a minimum impact value of 60 J are required to ensure reliable operation of the LNG tanks at operating temperature. Conventional arc welding processes including shielded metal arc welding (SMAW), gas metal arc welding (GMAW), gas tungsten arc welding (GTAW) and submerged arc welding (SAW) are currently used in construction of LNG tanks. Ni based filler wire is the preferred filler metal of choice in LNG tank construction. The main problem with this choice is the lower mechanical properties, particularly tensile strength of the weld metal. To compensate, the wall thickness needs to be excessively thick to ensure the strength of the welded structures. Ni based filler material is expensive and a large quantity is needed to fill the multi-pass weld grooves. These factors significantly add to the cost in the fabrication of LNG storage tanks. For these reasons, exploration of new welding technologies are a priority. A big potential can be seen in laser based welding techniques. Laser beam welding results in much smaller weld zone with chemical composition and mechanical properties similar to that of the base material. Laser welding is a much faster process and allows for a joint geometry which requires less filler material and fewer welding passes. The advantages of laser welding can help to overcome the problems pointed out above. Trials of autogenous laser welding, laser cold-wire welding and hybrid laser-arc welding (HLAW) conducted on the 9%Ni steel are presented in this paper. Chemical composition of the weld metal as well as effects of welding parameters on the weld formation, microstructure and tensile strength is discussed. Filler wire penetration depth as well as character of its distribution in the narrow laser welds was examined using Electron Probe Microanalysis (EPMA).
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