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    Item type:Publication, Access status: with files ,
    Process strategies for DED-Arc-manufactured preforms of Ti-15-3-3-3 in flowforming applications
    (Multidisciplinary Digital Publishing Institute (MDPI), 2026-06-02)
    Robert Lau
    ;
    Dahms, Frederik
    ;
    Hannes Zapf
    ;
    Henrik Wünsch
    ;
    Alexander Mädje
    Arc-based directed energy deposition (DED-Arc) processes represent a promising choice for developing flexible and eco-friendly manufacturing strategies for titanium components within the aerospace sector. Previous work has predominantly focused on using Ti-6Al-4V combined with machining for structural components. This study aims to establish a hybrid manufacturing route that integrates DED-Arc with flowforming (FF), focusing on the processability of Ti-15-3-3-3 in both stages. Sinusoidal path strategies for DED-Arc yield superior results in terms of process stability and geometrical accuracy, leading to near-net-shape preforms. In the FF process, a reduction of up to 80% in wall thickness across various techniques was achieved. The hybrid approach led to a buy-to-fly (BTF) ratio of 2.5:1, revealing the potential for significant material savings compared to conventional manufacturing routes.
    Publicationtype: Journal Article
      6  2
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    Item type:Publication, Access status: with files ,
    Significant improvement of the fatigue performance of ER70S-6 WAAM un-milled structures: a Cu/Ni multilayer nanotechnology approach
    (Elsevier, 2025-12-10)
    Falah, Mohsen
    ;
    Lau, Robert
    ;
    Spalek, Niclas
    ;
    Seidelmann, Maren
    ;
    Lalkovski, Nikolay
    In recent years, the adoption of Wire Arc Additive Manufacturing (WAAM), now defined as Directed Energy Deposition based on Gas Metal Arc Welding (DED-Arc), in steel construction has increased significantly. However, the sequential layer deposition inevitably creates surface notches that cause high stress concentrations, leading to fatigue crack initiation. The current industrial standard for post-processing, CNC milling, is time-consuming and resource-intensive. A novel research approach focuses on directly controlling critical residual stresses of as-built specimens by introducing near-surface compressive residual stresses using a Cu/Ni nanostructured metallic multilayer (NMM). This study investigates the effect of NMM on DED-Arc structures and extends its application to metallic 3D-printed components. Optical microscopy provides detailed surface morphology and reliable roughness measurements, while X-ray diffraction (XRD) confirms the presence of residual tensile stresses in the NMM and the resulting residual compressive stresses in the steel substrate. Preliminary tension-tension fatigue testing provides insights into the fatigue strength increase due to NMM treatment of DED-Arc dogbone specimen.
    Publicationtype: Journal Article
      37  16
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    Item type:Publication, Access status: with files ,
    Methodology for integrating biomimetic beams in abstracted topology optimization results
    (American Society of Mechanical Engineers (ASME), 2022-10)
    Röver, Tim
    ;
    Lau, Robert Johannes
    ;
    Lange, Fritz
    ;
    Struve, Arnd
    ;
    Fuchs, Cedrik
    This paper presents a five-step design methodology to generate designs of biomimetic structural components from topology optimization results. In step one, all material allocated by topology optimization is classified as either beam like structures or nodes to generate an auxiliary model consisting of preserved regions, cylindrical beams, and ball nodes, which is an abstraction of the original topology optimization result. In step two, the auxiliary model is exposed to the original boundary conditions in a finite element analysis. Then, internal forces, torsion, and bending moments in all beams of the auxiliary model are identified with respect to both of their ends. In step three, a database is used to find a suitable biomimetic beam for each previously analyzed beam in the auxiliary model. In step four, adapted nodes are designed to connect the biomimetic beams and preserved regions to generate an intermediate biomimetic component design. And in step five, a design iteration and a validation of the final design are performed. The design methodology allows for reproducible bio-mimetic component designs, a trackable and easily documentable component development process, and the possibility of automating the design process to ultimately save development costs when designing structural components.
    Publicationtype: Conference Paper
      55  175