Fraunhofer-Institut für Produktionsanlagen und Konstruktionstechnik IPK

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  • Publication
    Effects on the distortion of Inconel 718 components along a hybrid laser-based additive manufacturing process chain using laser powder bed fusion and laser metal deposition
    ( 2021)
    Uhlmann, E.
    ;
    Düchting, J.
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    Petrat, T.
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    Krohmer, E.
    ;
    Graf, B.
    ;
    Rethmeier, M.
    The combination of laser powder bed fusion (LPBF), 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 additive manufacturing times for large metallic parts. For the industrial application of the LPBF-LMD hybrid process chain, it is necessary to investigate the influence of the LMD process on the LPBF substrate. In addition, the build plate material also has a significant impact on the occurrence of distortion along the additive manufacturing process chain. In the literature, steel build plates are often used in laser-based additive manufacturing processes of Inconel 718, since a good metallurgical bonding can be assured whilst reducing costs in the production and restoration of the build plates. This paper examines the distortion caused by LMD material deposition and the influence of the build plate material along the hybrid additive manufacturing process chain. Twin cantilevers are manufactured by LPBF and an additional layer is subsequently deposited with LMD. The distortion is measured in the as-built condition as well as after heat treatment. The effect of different LMD hatch strategies on the distortion is determined. The experiments are conducted using the nickel-base alloy Inconel 718. The results show a significant influence of LMD path strategies on distortion, with shorter tool paths leading to less distortion. The remaining distortion after heat treatment is considerably dependent on the material of the build plate.
  • Publication
    Manufacturing of graphite electrodes with high geometrical requirements
    ( 2019)
    Uhlmann, E.
    ;
    Kuche, Y.
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    Polte, J.
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    Polte, M.
    Graphite is widely used for the die-sinking electrical discharge machining (EDM) process, especially for the roughing process. For the manufacturing of graphite electrodes the milling process is mainly used. The process enables fast processing times tP and high geometrical flexibility. In consequence of the cutting behaviour of graphite micro-components with geometrical features can be manufactured. In this contribution the manufacturing of micro-pins and bridges with aspect ratios of A = 1:50 were machined with diamond coated milling tools. By variation of the depth of cut ap and the width of cut ae it can be shown that the influence of the depth of cut ap is quite bigger than the influence of the width of cut ae. This results in consequence of the higher stability of the geometrical features by improved force distribution.
  • Publication
    Modelling of Abrasive Water Jet Cutting with Controlled Depth for Near-Net-Shape Fabrication
    ( 2019)
    Uhlmann, E.
    ;
    Männel, C.
    Near-net-shape fabrication of difficult to machine materials is a promising application for the abrasive water jet technology. An effective implementation can be achieved by controlling the kerf depth and cutting off defined material fragments. A model for controlled cutting is introduced to make the machining process design more effective for different materials. An empirical model was combined with the process' physical behavior, allowing the prediction of the kerf geometry using a minimum number of predictors and thus initial trials. The model tested with metal matrix composites, reveals the capability of transferring knowledge to new materials using few initial trials.
  • Publication
    Reconfiguring machine tool behavior via smart building block systems
    ( 2019)
    Uhlmann, E.
    ;
    Peukert, B.
    The reconfigurability of manufacturing systems is conventionally increased by utilizing concepts of modularization and platforms. At this moment, the actual reconfigurability is often limited to a priori designed reconfiguration variants for the production within single part families. There is only a little research on reconfiguring the mechanical behavior of machine tool frames. This paper presents an innovative approach for reconfiguring the mechanical behavior based on smart building block systems. Topologically optimized polyhedral building blocks are mechanically bolted to form different machine tool frame configurations. A high grade of modularization allows for the assembly of individualized topologies for different manufacturing scenarios "as needed when needed". The increase in reconfigurability results from the high geometric flexibility of the proposed building block system. However, successful implementation relies on quick and robust simulation approaches for calculating the machine tool frame characteristics before the actual assembly process. Within this paper, a time-efficient approach based on the sub-structuring methodology is utilized. The presented approach consists of forming superelements by performing a GUYAN reduction on the building blocks to extract the stiffness behavior. A Component Mode Synthesis is used to extract modal information. The ANSYS Parametric Design Language is then used to automatically couple the modules according to a customized descriptive machine tool language. A simple joint model is implemented and experimentally fitted with a two-block configuration. The two-block configuration is then extrapolated to a full machine tool frame portal. An example of changing the modal characteristics of this machine tool frame portal is presented in the form of numerical results.
  • Publication
  • Publication
    Ecological and functional optimization of the pretreatment process for plasma based coatings of cutting tools
    ( 2019)
    Uhlmann, E.
    ;
    Riemer, H.
    ;
    An, S.
    ;
    Fröhlich, M.
    ;
    Paschke, H.
    ;
    Petersen, M.
    Increasing demands in machining of high-tech materials and dry machining lead to higher thermal and mechanical loads on cutting tools. In response to these challenges, enhanced coating solutions are applied to increase performance and life of cutting tools. However, during the production process the cemented carbide substrates are contaminated with grinding oils and residues of organic material. For the subsequent physical vapor deposition (PVD) coating process an intensive and high-quality cleaning process is necessary. In this contribution, plasma electrolytic polishing (PEP) is used as a novel alternative to conventional ecologically harmful cleaning baths. Apart from the ecological advantage, the surface of the substrate can be optimized with regard to the coating adhesion. To examine the performance of the different cleaning processes, machining tests were performed at the IWF to evaluate the layer adhesion and tool life of the tools.
  • Publication
    Rheological and Mechanical Gradient Properties of Polyurethane Elastomers for 3D-Printing with Reactive Additives
    ( 2019)
    Wang, P.
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    Auhl, D.
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    Uhlmann, E.
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    Gerlitzky, G.
    ;
    Wagner, M.H.
    Polyurethane (PU) elastomers with their broad range of strength and elasticity are ideal materials for additive manufacturing of shapes with gradients of mechanical properties. By adjusting the mixing ratio of different polyurethane reactants during 3D-printing it is possible to change the mechanical properties. However, to guarantee intra-and inter-layer adhesion, it is essential to know the reaction kinetics of the polyurethane reaction, and to be able to influence the reaction speed in a wide range. In this study, the effect of adding three different catalysts and two inhibitors to the reaction of polyurethane elastomers were studied by comparing the time of crossover points between storage and loss modulus G' and G'' from time sweep tests of small amplitude oscillatory shear at 30°C. The time of crossover points is reduced with the increasing amount of catalysts, but only the reaction time with one inhibitor is significantly delayed. The reaction time of 90% NCO group conversion calculated from the FTIR-spectrum also demonstrates the kinetics of samples with different catalysts. In addition, the relation between the conversion as determined from FTIR spectroscopy and the mechanical properties of the materials was established. Based on these results, it is possible to select optimized catalysts and inhibitors for polyurethane 3D-printing of materials with gradients of mechanical properties.
  • Publication
    Elektromechanisches Glattwalzen von Stahllegierungen
    ( 2019)
    Uhlmann, E.
    ;
    Thom, S.
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    Prasol, L.
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    Haberbosch, K.
    ;
    Drieux, S.
  • Publication
    Safety of slim tool extensions for milling operations
    ( 2019)
    Uhlmann, E.
    ;
    Thom, S.
    ;
    Barth, E.
    ;
    Pache, T.
    ;
    Prasol, L.
    The development of 5-axis machine tools (MT) allows complete machining of complex workpiece geometries. In order to counteract lacking operation space and to improve the accessibility of the workpiece, slim tool extensions (STE) are applied. Operating errors, e.g. by crash, can cause plastic deformation of STE during machining operation and therefore lead to an increased moment of inertia, and thus to rotational energy due to the spindle speed control of machine tools. Currently applied machine tool enclosures are not designed for such failures with corresponding kinetic energies EKIN. The described failure implies a risk potential for operators and a high damage potential for machine tools. In this paper, the failure scenario is identified and modeled. This includes the calculation of elastoplastic deformations of STE based on finite element analysis and analytical calculation of kinetic energies EKIN considering deformed STE. Based on the described model a parameter study is carried out considering the geometry of the STE as well as the spindle speed nS. The safety of existing machine tool enclosures is evaluated according to DIN EN 12417 in order to identify safe operating conditions. Finally, the authors suggest possible solutions addressing both, the STE and machine tool enclosure. The research presented in this paper is funded by the German Machine Tool Builders Association (VDW).