Fraunhofer-Institut für Produktionsanlagen und Konstruktionstechnik IPK

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  • Publication
    Integrated weld preparation designs for the joining of L-PBF and conventional components via TIG welding
    ( 2022-04-18)
    Geisen, Ole
    ;
    Müller, Vinzenz
    ;
    Graf, Benjamin
    ;
    Rethmeier, Michael
    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
    Characterization of Ti-6Al-4V Fabricated by Multilayer Laser Powder-Based Directed Energy Deposition
    ( 2022)
    Ávila Calderón, Luis Alexander
    ;
    Graf, Benjamin
    ;
    Rehmer, Birgit
    ;
    Petrat, Torsten
    ;
    Skrotzki, Birgit
    ;
    Rethmeier, Michael
    Laser powder-based directed energy deposition (DED-L) is increasingly being used in additive manufacturing (AM). As AM technology, DED-L must consider specific challenges. It must achieve uniform volume growth over hundreds of layers and avoid heat buildup of the deposited material. Herein, Ti-6Al-4V is fabricated using an approach that addresses these challenges and is relevant in terms of transferability to DED-L applications in AM. The assessment of the obtained properties and the discussion of their relationship to the process conditions and resulting microstructure are presented. The quality of the manufacturing process is proven in terms of the reproducibility of properties between individual blanks and with respect to the building height. The characterization demonstrates that excellent mechanical properties are achieved at room temperature and at 400 C.
  • Publication
    Heat treatment of SLM-LMD hybrid components
    ( 2019)
    Uhlmann, Eckart
    ;
    Düchting, Jan
    ;
    Petrat, Torsten
    ;
    Graf, Benjamin
    ;
    Rethmeier, Michael
    Additive manufacturing is no longer just used for the production of prototypes but already found its way into the industrial production. However, the fabrication of massive metallic parts with high geometrical complexity is still too time-consuming to be economically viable. The combination of the powder bed-based selective laser melting process (SLM), known for its geometrical freedom and accuracy, and the nozzle-based laser metal deposition process (LMD), known for its high build-up rates, has great potential to reduce the process duration. For the industrial application of the SLM-LMD hybrid process chain it is necessary to investigate the interaction of the processes and its effect on the material properties to guarantee part quality and prevent component failure. Therefore, hybrid components are manufactured and examined before and after the heat treatment regarding the microstructure and the hardness in the SLM-LMD transition zone. The experiments are conducted using the nickel-based alloy Inconel 718.
  • Publication
    Numerische Simulation einer AM-Prozesskette im DED Auftragschweißen
    ( 2019)
    El-Sari, Bassel
    ;
    Biegler, Max
    ;
    Graf, Benjamin
    ;
    Rethmeier, Michael
    Das DED Auftragschweißen ist ein additives Fertigungsverfahren für Metalle, bei dem das Material schichtweise auf ein Substrat aufgetragen wird. Die schnellen Temperaturzyklen rufen Spannungsgradienten im Bauteil hervor. Der schichtweise Aufbau der Bauteile verursacht eine anisotrope Mikrostruktur. Mittels nachgelagerter Wärmebehandlung können diese Effekte verringert werden. Im anschließenden Schritt der Prozesskette wird das additiv hergestellte Bauteil mittels Drahterodieren von dem Substrat abgetrennt. In diesem Beitrag wird eine thermo-mechanische Simulation der gesamten Prozesskette vorgestellt, welche den additiven Aufbau, Wärmebehandlung und das Abtrennen vom Substrat beinhaltet. Anstelle der in der Literatur üblichen schichtweisen Modellierungsstrategie für die DED Simulation wird das gesamte Bauteil in einem Stück vernetzt und der vollständig transiente, schichtweise Materialauftrag über Elementgruppen realisiert. Im Gegensatz zu früheren Simulationen muss der nichtlineare Kontakt zwischen den Schichten nicht berücksichtigt werden, was die Rechenzeiten deutlich verkürzt. Das Modell wurde validiert mittels Abgleiches des Verzugs aus Simulation und Experiment. Die Proben, bestehend aus DIN 1.4404 (AISI 316L), wurden nach jedem Prozessschritt 3D gescannt um den Verzug zu quantifizieren. Zusätzlich wurden Querschnitte und Härtetests nach Vickers von unterschiedlich behandelten Proben durchgeführt, um den Effekt der Wärmebehandlung auf die Mikrostruktur und die Härte des Bauteils zu untersuchen.
  • Publication
    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.
  • Publication
    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.
  • Publication
    Highspeed-Plasma-Laser-Cladding (HPLC) als hybrides Beschichtungsverfahren: Evaluierung des Einsatzpotentials für hohe Prozessgeschwindigkeiten
    ( 2019)
    Brunner-Schwer, Christian
    ;
    Schreiber, Frank
    ;
    Graf, Benjamin
    ;
    Rethmeier, Michael
    Das Plasma-Pulver-Auftragschweißen ist ein Verfahren, dass hohe Auftragraten ermöglicht, jedoch auch eine erhöhte thermische Belastung des Bauteiles verursacht. Laser-Pulver- Auftragschweißen hingegen erreicht eine hohe Präzision und eine geringe Aufmischung, erfordert jedoch ein kostspieliges Hochleistungslasersystem und erreicht im Vergleich nur geringe Auftragraten, was zu hohen Verarbeitungskosten führt. Eine Kopplung von Laser- und Lichtbogenenergie in einer gemeinsamen Prozesszone zielt darauf ab, die jeweiligen Vorteile beider Technologien zu nutzen. Dies betrifft insbesondere die Effizienz der Wärmeausnutzung und der Nutzung des Zusatzwerkstoffs. Es wird ein Plasma-Laser-Hybrid-Prozess als Highspeed-Plasma-Laser-Cladding-Technologie (HPLC) für Beschichtungs- sowie Instandsetzungszwecke vorgestellt. Gezeigt werden Ergebnisse mit Prozessgeschwindigkeiten von 10 m/min bei Laserleistungen von 2 kW, dabei können Flächenraten von mehr als 1 m2/h erreicht werden. Effiziente Beschichtungen von großen Flächen, beispielsweise auf rotationssymmetrischen Bauteilen stellen ein relevantes Anwendungsfeld für diesen Technologieansatz dar. Die Nickelbasislegierung Inconel 625 wird als Korrosionsschutzwerkstoff eingesetzt. Im Rahmen der Verfahrensprüfung werden die hergestellten Beschichtungen einer EDX Messung unterzogen. Prozesscharakteristische Kenngrößen wie z.B. die Auftragrate werden vorgestellt und vor dem Hintergrund wirtschaftlicher Kennzahlen diskutiert. Zusätzlich werden die Aufmischung, Spurgeometrie und Wärmeeinflusszone der Spuren und Schichten ausgewertet. Im Vergleich zum Laser-Pulver-Auftragschweißen werden Spuren bei hohen Prozessgeschwindigkeiten mit einer hohen Auftragrate erzeugt.
  • Publication
    Automated tool-path generation for rapid manufacturing and numerical simulation of additive manufacturing LMD geometries
    ( 2019)
    Biegler, Max
    ;
    Wang, Jiahan
    ;
    Graf, Benjamin
    ;
    Rethmeier, Michael
    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)
  • Publication
    Finite element analysis of in-situ distortion and bulging for an arbitrarily curved additive manufacturing directed energy deposition geometry
    ( 2018)
    Biegler, Max
    ;
    Marko, Angelina
    ;
    Graf, Benjamin
    ;
    Rethmeier, Michael
    With the recent rise in the demand for additive manufacturing (AM), the need for reliable simulation tools to support experimental efforts grows steadily. Computational welding mechanics approaches can simulate the AM processes but are generally not validated for AM-specific effects originating from multiple heating and cooling cycles. To increase confidence in the outcomes and to use numerical simulation reliably, the result quality needs to be validated against experiments for in-situ and post process cases. In this article, a validation is demonstrated for a structural thermomechanical simulation model on an arbitrarily curved Directed Energy Deposition (DED) part: at first, the validity of the heat input is ensured and subsequently, the model's predictive quality for in-situ deformation and the bulging behaviour is investigated. For the in-situ deformations, 3D-Digital Image Correlation measurements are conducted that quantify periodic expansion and shrinkage as they occur. The results show a strong dependency of the local stiffness of the surrounding geometry. The numerical simulation model is set up in accordance with the experiment and can reproduce the measured 3 dimensional in-situ displacements. Furthermore, the deformations due to removal from the substrate are quantified via 3D scanning, exhibiting considerable distortions due to stress relaxation. Finally, the prediction of the deformed shape is discussed in regards to bulging simulation: to improve the accuracy of the calculated final shape, a novel extension of the model relying on the modified stiffness of inactive upper layers is proposed and the experimentally observed bulging could be reproduced in the finite element model.