Fraunhofer-Institut für Produktionsanlagen und Konstruktionstechnik IPK

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  • Publication
    Edge Computing Software für den Zerspanungsprozess
    ( 2023)
    Uhlmann, Eckart
    ;
    Hocke, Toni
    ;
    Heper, Martin
    ;
    Polte, Mitchel
    In aktuellen Forschungsprojekten entwickeln Forscher des Instituts für Werkzeugmaschinen und Fabrikbetrieb (IWF) Open-Source-Software für Edge Devices. Für die Auslegung der Fertigungsprozesse wird neben den ingenieurwissenschaftlichen Themen auch exemplarisch die Auslegung einer entwickelten Auswerteelektronik inklusive der Softwarebereitstellung adressiert. Der interdisziplinäre Ansatz, einschließlich der Softwarebereitstellung, wird exemplarisch an einem DFG-Projekt zur Prozessüberwachung bei der Ultrapräzisionsdrehbearbeitung diskutiert.
  • Publication
    Echtzeit-Energieüberwachung in der Funkenerosion
    ( 2023)
    Uhlmann, Eckart
    ;
    Polte, Mitchel
    ;
    Yabroudi, Sami
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    Thißen, Kai
    ;
    Penske, Wilhelm
    Ein großes Optimierungspotenzial der Funkenerosion liegt in den Energien der einzelnen Entladungen verborgen. Eine vektorielle Bestimmung der Entladedauern und die darauf basierende Energieberechnung sowie Klassifizierung erlauben es, die Entladeenergien, Entladungsarten und -dauern in Echtzeit zu überwachen und zu analysieren. Möglich wird dies durch ein Multiprocessing-Erzeuger-Verbraucher-Schema, welches überdies eine Visualisierung und Auswertung der Messdaten erlaubt.
  • Publication
    Simulativer Vergleich tubularer Peltierelemente
    ( 2022)
    Binninger, Roland
    ;
    Pernau, Hans-Fridtjof
    ;
    Schäfer-Welsen, Olaf
    ;
    Triebel, Florian
    ;
    Polte, Mitchel
    ;
    Uhlmann, Eckart
    Der Einsatz von Peltierelementen bietet in der Temperierung von Prozessen und Bauteilen einen großen Vorteil gegenüber der in technischen Anwendungen üblicherweise eingesetzten Fluidkühlung. Sie pumpen Wärme rein elektrisch und stellen Temperaturen sehr schnell sowie präzise ein. Für eine neuartige, thermoelektrisch temperierte Motorspindel wurden in Kooperation zwischen dem Fraunhofer-Institut für Physikalische Messtechnik IPM und dem Institut für Werkzeugmaschinen und Fabrikbetrieb IWF der Technischen Universität Berlin zwei unterschiedliche Ansätze tubularer Peltierelemente simulativ verglichen. Die Ergebnisse zeigen, dass es mit beiden Konzepten möglich ist, induzierte Wärmeströme am Lagersitz abzu­führen, um diesen auf eine vorgegebene Temperatur zu regeln.
  • Publication
    Novel Advances in Machine Tools, Tool Electrodes and Processes for High-Performance and High-Precision EDM
    ( 2022)
    Uhlmann, Eckart
    ;
    Polte, Mitchel
    ;
    Yabroudi, Sami
    High-performance electrical discharge machining (EDM) is a key technology for manufacturing high-precision components in a broad range of industrially relevant applications. Formation of debris in the working gap leads to arcing and short-circuits on the surface as well as related inaccuracies and process instabilities. Despite decades of research in the field of EDM excessive tool wear and limited process performance are still challenging. In order to overcome highly complex state-of-the-art challenges, dedicated processes, machine tools, peripheral systems, software, tool electrodes and technologies for the application of alternative dielectric fluids have been developed. Within this work novel advances in the development of a sophisticated dry EDM machine tool, including generator and process control technology based on open architecture, open source software, and commonly available machine tool components, are presented. Solutions for challenges regarding remaining debris and gas bubbles as well as related arc discharge and short-circuit pulses in sinking EDM are presented by new flushing methods, technologies and devices. A new system for inverted pressure flushing of a dielectric fluid in ED-drilling enables a highly efficient removal of debris and gas bubbles through the interior channels of the tool electrode. A new multi-luidic spindle system for EDM provides the ability to use performance- and material-related application of gaseous, near-dry and liquid dielectric fluids sequentially within a single machining process. Recent advances in tool electrode design, tool electrode material application, modification and production have led to essential process improvements. A helical tool electrode design significantly improved flushing conditions and related material removal rate in ED-drilling. Modification of ED-drilling tool electrode surfaces by thermal oxidation of copper reveals a promising approach to minimize ineffective discharges. Application of a specific mesophase-pitch carbon fiber with a diameter of df = 10 µm using a new process and handling technology enabled drilling holes with a diameter of dh = 25 µm. Next to the shown advances in EDM, efficient development of new process technologies could be enabled by using a specially adapted natural analogue algorithm software tool.
  • Publication
    Comparing the performance of a nested to a continuous evolution strategy with covariance matrix adaption for optimization of drilling EDM
    ( 2022)
    Uhlmann, Eckart
    ;
    Streckenbach, Jan
    ;
    Polte, Mitchel
    ;
    Osmanovic, M.
    ;
    Schick, F.
    Electrical discharge machining (EDM) is a complex manufacturing process where the correlation of the individual process parameters is not fully known. When introducing new materials or complex, individual geometries in EDM, a satisfactory vector of parameters for the process must be found. This challenge is often encountered in the aerospace industry as well as in mold and tool making. One previously successful method to tackle this challenge is the stochastic optimization procedure Evolutionary Strategy (ES). Utilizing an appropriately chosen objective function, the search for a suitable vector of input parameters may be formulated as a mathematical minimization problem over the parameter space. The ES with a covariance matrix adaption (CMA) was utilized to sample from this parameter space in a stochastic manner. Examining the impact of the CMA within an ES is a promising way to gain better insight into the performance of ES. For this purpose, a vector of input parameters was optimized for a drilling EDM process with a comma and a nested comma ES with CMA. It was found that the comma ES led to a reduction in erosion duration tero of 38 % compared to the initially chosen parameters and the nested comma ES led to a reduction in erosion duration tero of 27 % compared to the same initial parameters. The additional information stored in the covariance matrix enables the ES to find a local optimum of the parameter vector faster and more consistently. This fact is verified by use of visualizations of the covariance matrix on a two-dimensional subspace. From these findings it can be concluded, that for the application of the ES to the optimization of EDM processes the CMA should be performed continuously over all generations as opposed to resetting this matrix after a number of generations.
  • Publication
    High-Performance Electro-Discharge Drilling with a Novel Type of Oxidized Tool Electrode
    ( 2022)
    Uhlmann, Eckart
    ;
    Polte, Julian
    ;
    Streckenbach, Jan
    ;
    Dinh, Ngoc Chuong
    ;
    Yabroudi, Sami
    ;
    Polte, Mitchel
    ;
    Börnstein, Julian
    Electro-discharge drilling is a key technology for manufacturing sophisticated nozzles in a broad range of automotive and aerospace applications. The formation of debris in the working gap leads to arcs and short circuits on the lateral surface when state-of-the-art tool electrodes are used. As a result, limited drilling depth, increased linear tool wear, and the conicity of boreholes are still challenges. In this work, a new approach for the passivation of the lateral surface of copper tool electrodes by oxidation is shown. The comparison with state-of-the-art tool electrodes showed a reduction in the erosion duration by 48% for machining hardened steel. Promising improvements could be achieved by the thermal oxidation of the tool electrodes with the aim of increasing the electrical resistivity of the lateral surface of the tool electrode. However, due to the loss of strength, the high oxide layer thickness, and the partial delamination of the oxide layer, further comprehensive investigations on the influence of the oxidation temperature need to be conducted. Future adjustments with lower oxidation temperatures will be carried out.
  • Publication
    Validation of different tungsten carbide-cobalt grades as tool electrode material for sinking EDM
    ( 2022)
    Uhlmann, Eckart
    ;
    Bolz, Robert
    ;
    Polte, Mitchel
    ;
    Börnstein, Julian
    In sinking electrical discharge machining (EDM), tool electrode wear is crucial for an economical production. The tool electrode wear affects the process efficiency and determines the number of required tool electrodes for a specific machining process. Therefore, the relative tool wear, describing the relation of removed material volume between tool and workpiece electrode, needs to be minimised. The tool wear characteristics in sinking EDM depend strongly on EDM processing parameters and the applied electrode materials. Especially in micro-EDM, a significant increase of relative tool wear is representative. Because of its thermophysical properties tungsten carbide-cobalt (WC-Co) is a suitable material for the application as sinking EDM tool electrode. The economical production of WC-Co form electrodes for EDM sinking is enabled by recent advancements in precision milling of hard materials. Due to non-existent research on which composition of WC-Co is most advantageous for the application as sinking EDM tool electrode material, previous investigations have been intensified to describe correlations between material properties, EDM processing parameters and EDM processing results concerning material removal rate and relative tool wear. Therefore, various WC-Co grades with differing grain size and cobalt content were analysed in sinking EDM experimental studies. It was observed that the factor grain size showed an ambiguous effect concerning the process results. An increasing cobalt content led to a reduction of relative tool wear, which can be explained by the microstructure of the cobalt binder phase with its higher electrical conductivity. The WC-Co grades with beneficial EDM processing results have been further investigated in EDM parameter studies with differing tool electrode geometries. The experimental results concerning relative tool wear, with a minimum of 3 % for macro- and 5 % for micro-sized geometries, proved the suitability of specific WC-Co compositions as tool electrode material for sinking EDM.
  • Publication
    Modeling of the wet immersed tumbling process with the Discrete Element Method (DEM)
    ( 2021)
    Uhlmann, Eckart
    ;
    Fürstenau, J.-P.
    ;
    Kuche, Yves
    ;
    Yabroudi, Sami
    ;
    Polte, Julian
    ;
    Polte, Mitchel
    Immersed tumbling is an industrially established process for finishing of components made of metal, ceramic or plastic. In this process, the components are completely surrounded by a wet, abrasive medium, which allows burrs to be removed and surfaces to be polished. In order to gain specific insights into the influence and flow properties of the abrasive media used in this process, numerical approaches using the Discrete Element Method (DEM) with the Rocky DEM software are presented within these investigations. A complete process simulation could be realised by means of a digital machine tool. The immersed tumbling process with cone-shaped polymer abrasive media is implemented by use of a liquid bridge model. The results were validated by experiments with an industrially used immersed tumbling machine tool and for the first time allow sound statements about the contact conditions and interactions of the abrasive media with the workpiece.
  • Publication
    Accuracy in force estimation applied on a piezoelectric fine positioning system for machine tools
    ( 2021)
    Uhlmann, Eckart
    ;
    Polte, Mitchel
    ;
    Triebel, Florian
    ;
    Overbeck, Rasmus
    ;
    Thom, Simon
    In order to improve the accuracy of machine tools, the use of additional active modules meeting the requirements of the ""Plug & Produce"" approach is focused. In this context one approach is the installation of a high precision positioning table for online compensation of machine tool deflections. For the model-based determination of the deflection, the knowledge of the effecting process force is crucial. This article examines the use of displacement sensors for force estimation in a piezoelectric system. The method is implemented on a high precision positioning table applicable in milling machine tools. In order to compensate nonlinear effects of piezoelectric actuators, a hysteresis operator is implemented. Experimental investigations are carried out to quantify the influence of preload stiffness, preload force and workpiece weight. Finally, a resolution d < 78 N could be achieved and further improvements to meet the requirements for online compensation of machine tool deflection are discussed.
  • Publication
    Hyperparameter Optimization of Artificial Neural Networks to Improve the Positional Accuracy of Industrial Robots
    ( 2021)
    Uhlmann, Eckart
    ;
    Polte, Mitchel
    ;
    Blumberg, Julian
    ;
    Li, Zhoulong
    ;
    Kraft, Adrian
    Due to the rising demand for individualized product specifications and short innovation cycles, industrial robots gain increasing attention for machining operations as milling and forming. Limitations in their absolute positional accuracy are addressed by enhanced modelling and calibration techniques. However, the resulting absolute positional accuracy stays in a range still not feasible for general purpose milling and forming tolerances. Improvements of the model accuracy demand complex, often not accessible system knowledge on the expense of realtime capability. This article presents a new approach using artificial neural networks to enhance positional accuracy of industrial robots. A hyperparameter optimization is applied, to overcome the downside of choosing an appropriate artificial neural network structure and training strategy in a trial and error procedure. The effectiveness of the method is validated with a heavy-duty industrial robot. It is demonstrated that artificial neural networks with suitable hyperparameters outperform a kinematic model with calibrated geometric parameters.