Fraunhofer-Institut für Produktionsanlagen und Konstruktionstechnik IPK

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Process advantages of laser hybrid welding compared to conventional arc-based welding processes for joining thick steel structures of wind tower

2023-12-22 , Brunner-Schwer, Christian , Üstündag, Ömer , Bakir, Nasim , Gumenyuk, Andrey , Rethmeier, Michael

The most common welding processes when joining thick-walled steels in the industry are arc-based welding processes such as GMAW or SAW. For this purpose, the sheets are joined in multi-layer technique, which can lead to productivity losses due to high welding times. The process-specific challenges in welding thick steels using multi-layer technique relate to the high heat input from the process. Therefore, alternative welding processes are being actively sought. A suitable alternative is provided by beam-based welding processes such as the laser hybrid welding processes, which are characterized by deep penetration welds and lower heat input. With implementation of the laser hybrid welding process in the heavy industry, such as the wind tower industry, economic benefits can be reached such as the increase in productivity by reducing the layer number, and the lower consumption of filler material and energy. When comparing SAW welded 25 mm thick steels in five to six layers and single-pass laser hybrid welding, the welding time can be reduced more than 80 % and the costs of filler material, flux and energy can be saved up to 90 %. However, the industrial use of the laser hybrid welding process is still limited to applications, where the material thickness does not exceed 15 mm due to some process-specific challenges such as the sagging, sensitivity to manufacturing tolerances such as gaps and misalignment, limited filler wire mixing, and deteriorated mechanical properties resulting from high cooling rates. To overcome these challenges, a contactless electromagnetic backing based on an externally applied AC magnetic field was used. Eddy currents are induced due to the oscillating magnetic field, and an upward-oriented Lorentz force is generated to counteract the droplets formed due to gravitational forces. It allows to weld up to 30 mm thick structural steels in a single-pass with a 20-kW fiber laser system. Additionally, the gap bridgeability and the misalignment of edges were increased to 2 mm when welding 20 mm thick steels. With the aid of the AC magnetic field, a vortex was formed in the weld root, which had a positive effect on the filler wire mixing.

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Laser Welding of L-PBF AM components out of inconel 718

2022 , Brunner-Schwer, Christian , Simón-Muzás, Juan , Biegler, Max , Hilgenberg, Kai , Rethmeier, Michael

With regard to efficient production, it is desirable to combine the respective advantages of additively and conventionally manufactured components. Particularly in the case of large-volume components that also include filigree or complex structures, it makes sense to divide the overall part into individual elements, which afterwards have to be joined by welding. The following research represents a first step in fundamentally investigating and characterizing the joint welding of Laser Powder Bed Fusion (L-PBF) components made of Inconel 718. For this purpose, bead-on-plate welds were performed on plates manufactured using the L-PBF process and compared with the conventionally manufactured material. Conventional laser beam welding was used as welding process. The weld geometry was investigated as a function of the L-PBF build-up orientation. It was found that the welding depth and weld geometry differ depending on this orientation and in comparison to the conventional material.

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Highspeed-plasma-laser-cladding of thin wear resistance coatings: A process approach as a hybrid metal deposition-technology

2019 , Brunner-Schwer, Christian , Petrat, Torsten , Graf, Benjamin , Rethmeier, Michael

Plasma-Transferred-Arc (PTA) welding is a process that enables high deposition rates, but also causes increased thermal load on the component. Laser metal deposition (LMD) welding, on the other hand, reaches a high level of precision and thus achieves comparatively low deposition rates, which can lead to high processing costs. Combining laser and arc energy aims to exploit the respective advantages of both technologies. In this study, a novel approach of this process combination is presented using a PTA system and a 2 kW disk laser. The energy sources are combined in a common process zone as a high-speed plasma laser cladding technology (HPLC), which achieves process speeds of 10 m/min at deposition rates of 6.6 kg/h and an energy per unit length of 39 J/mm.

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On Welding of High-Strength Steels Using Laser Beam Welding and Resistance Spot Weld Bonding with Emphasis on Seam Leak Tightness

2023 , Schmolke, Tobias , Brunner-Schwer, Christian , Biegler, Max , Rethmeier, Michael , Meschut, Gerson

The design of most electric vehicles provides for the positioning of the heavy energy storage units in the underbody of the cars. In addition to crash safety, the battery housing has to meet high requirements for gas tightness. In order to test the use of high-strength steels for this sub-assembly, this paper examines welded joints utilizing resistance spot weld bonding and laser remote welding, with special regard to the gas tightness of the welds. For this purpose, the pressure difference test and helium sniffer leak detection are presented and applied. The combination of both leak test methods has proven ideal in experimental investigations. For laser remote welding, gas-tight seams can be achieved with an inter-sheet gap of 0.1 mm, even if occasionally leaking samples cannot be prevented. Resistance spot welding suits gas-tight joining with both one- and two-component adhesives. Against the background of leak tightness, process fluctuations that lead to weld spatter and defects in the adhesive layer must be prevented with high priority.

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Entwicklung des hybriden Auftragschweißens als leistungsfähigen Beschichtungsprozess für Korrosions und Verschleißschutzschichten

2020 , Brunner-Schwer, Christian , Graf, Benjamin , Rethmeier, Michael

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Laser-plasma-cladding as a hybrid metal deposition-technology applying a SLM-produced copper plasma nozzle

2018 , Brunner-Schwer, Christian , Kersting, Robert , Graf, Benjamin , Rethmeier, Michael

Laser-Metal-Deposition (LMD) and Plasma-Transferred-Arc (PTA) are well known technologies which can be used for cladding purposes. The prime objective in combining LMD and PTA as a Hybrid Metal Deposition-Technology (HMD) is to achieve high deposition rates at low thermal impact. Possible applications are coatings for wear protection or repair welding for components made of steel. The two energy sources (laser and plasma arc) build a joint process zone and are configurated to constitute a stable process at laser powers between 0.4-1 kW (defocused) and plasma currents between 75-200 A. Stainless steel 316L serves as filler material. For this HMD process, a plasma Cu-nozzle is designed and produced by powder bed based Selective Laser Melting. The potential of the HMD technology is investigated and discussed considering existing processes. This paper demonstrates how the interaction of the two energy sources effects the following application-relevant properties: deposition rate, powder efficiency and energy input.

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Laserstrahlhybridschweißen von Türmen für Windkraftanlagen

2022-08-29 , Üstündag, Ömer , Bakir, Nasim , Brunner-Schwer, Christian , Knöfel, Frieder , Gook, Sergej , Rethmeier, Michael , Gumenyuk, Andrey

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.

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Microstructure of Inconel 718 parts with constant mass energy input manufactured with direct energy deposition

2019 , Petrat, Torsten , Brunner-Schwer, Christian , Graf, Benjamin , Rethmeier, Michael

The laser-based direct energy deposition (DED) as a technology for additive manufacturing allows the production of near net shape components. Industrial applications require a stable process to ensure reproducible quality. Instabilities in the manufacturing process can lead to faulty components which do not meet the required properties. The DED process is adjusted by various parameters such as laser power, velocity, powder mass flow and spot diameter, which interact with each other. A frequently used comparative parameter in welding is the energy per unit length and is calculated from the laser power and the velocity in laser welding. The powder per unit length comparative parameter in the DED process has also be considered, because this filler material absorbs energy in addition to the base material. This paper deals with the influence of mass energy as a comparative parameter for determining the properties of additively manufactured parts. The same energy per unit length of 60 J/mm as well as the same powder per unit length of 7.2 mg/mm can be adjusted with different parameter sets. The energy per unit length and the powder per unit length determine the mass energy. The laser power is varied within the experiments between 400 W and 900 W. Energy per unit length and powder per unit length are kept constant by adjusting velocity and powder mass flow. Using the example of Inconel 718, experiments are carried out with the determined parameter sets. In a first step, individual tracks are produced and analyzed by means of micro section. The geometry of the tracks shows differences in height and width. In addition, the increasing laser power leads to a higher dilution of the base material. To determine the suitability of the parameters for additive manufacturing use, the individual tracks are used to build up parts with a square base area of 20×20 mm². An investigation by Archimedean principle shows a higher porosity with lower laser power. By further analysis of the micro sections, at low laser power, connection errors occur between the tracks. The results show that laser power, velocity and powder mass flow must be considered in particular, because a constant mass energy can lead to different geometric as well as microscopic properties.

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