Fraunhofer-Institut für Produktionsanlagen und Konstruktionstechnik IPK

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Publication

Oxidized tool electrodes for optimized electro-discharge drilling

2020 , Uhlmann, Eckart , Polte, Mitchel , Streckenbach, Jan , Dinh, Ngoc Chuong , Börnstein, Julian , Wolf, Cora-Sophia , Camin, Bettina

The production of components for automotive and aerospace industry by conventional machining is still limited by hardness and strength of the workpiece materials. Electro-discharge drilling is used for machining electrically conductive materials without any limitation due to mechanical properties. Electro-discharge drilling causes debris in the working gap, which leads to arcs and short circuits on the lateral surface with negative effects on processing results and process duration. Due to these arcs and short circuits limited drilling depth, increased tool wear, conicity of boreholes and process instabilities are still challenges in electro-discharge drilling. In this work, a new approach for passivation of the tool electrode material by oxidation is shown. Different oxidation processes for tool electrodes made of brass were applied and analysed. Surface modified tool electrodes were used for electro-discharge drilling of Elmax, SuperClean from the company VOELSTAPINE AG, Linz, Austria. The investigation was carried out on the machine tool AGIETRON Compact 1 from the company AGIE SA, Losone, Switzerland, for machining of through holes with a depth of t = 33.5 mm using different surface modified tool electrodes with a diameter of d = 0.8 mm. First results show a reduction of the erosion duration by 20 % for the application of thermally oxidized brass. The investigation of different defined oxide layer thicknesses and electrical resistances for specific applications are part of this ongoing work. This work is funded by the German Research Foundation (DFG).

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Patent

Verfahren zur Herstellung einer Werkzeugelektrode und Verfahren zur ihrer Verwendung

2019 , Streckenbach, Jan , Wolf, Cora-Sophia , Börnstein, Julian , Uhlmann, Eckart

Die Erfindung bezieht sich auf ein Verfahren zur Herstellung einer Werkzeugelektrode (1) zum funkenerosiven Senken eines Werkstücks (10) mit dem Ziel der Erzeugung einer Ausnehmung/Senkung (11) in dem Werkstück, welche eine Grundfläche (4) und Seitenflächen (5) aufweist, wobei die Werkzeugelektrode eine Frontfläche (2) aufweist, die der zu erodierenden Fläche (4) oder der Grundfläche des Werkstücks zugewandt ist, sowie eine oder mehrere Mantelflächen (3), die während des Senkungsprozesses den Seitenflächen (5) der im Werkstück erodierten Ausnehmung/Senkung zugewandt sind. Eine deutliche Verbesserung des Funkenerosionsprozesses unter Einsatz der Werkzeugelektrode (1) wird dadurch erreicht, dass eine oder mehrere Mantelflächen (3) der Werkzeugelektrode (1) wenigstens teilweise mit einer Substanz in Kontakt gebracht werden, die mit dem Material der Werkzeugelektrode unter Ausbildung einer elektrisch isolierenden Reaktionsschicht, insbesondere eines Oxids, reagiert.

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Publication

Fundamental research of applying tungsten carbide-cobalt as tool electrode material for sinking EDM

2020 , Uhlmann, Eckart , Polte, Mitchel , Bolz, Robert , Börnstein, Julian

The manufacturing process milling is limited in machining specific geometries like inner contours with sharp edges, high aspect ratios or defined radii. Sinking EDM (S-EDM) is an appropriate process to machine complex features if the negative geometry is machinable. The tool electrode wear is a critical factor, because it affects machining accuracy and process efficiency. The tool electrode wear depends on S-EDM processing parameters, the geometry and material of the tool electrode. The material tungsten carbide-cobalt owns suitable thermophysical properties for the application as tool electrode material in EDM. Most applications of tungsten carbide-cobalt in EDM are limited to EDM drilling processes, where tungsten carbide tube electrodes are widely used. The advancements in milling of hard materials enable an economic manufacturing of tungsten carbide-cobalt form electrodes for sinking EDM applications. However, it is not investigated which composition of the material tungsten carbide-cobalt is the most appropriate for the application as tool electrode material in S-EDM. Additionally, there are no suitable EDM process parameters in order to benefit from the material characteristics of the respective tungsten carbide-cobalt. Focus of this work is the analysis of different tungsten carbide grades regarding the average grain size and the cobalt content in order to identify correlations between the material characteristics and the EDM process results. Therefore, eight different tungsten carbide grades with four different grain sizes and five different cobalt contents were applied in S-EDM experimental analysis. The experimental studies showed a general suitability of tungsten carbide-cobalt tool electrodes for EDM-processing, where the material removal rate is comparable to commonly used tool electrode materials. Nevertheless, the relative tool wear shows inferior results. It could be observed that higher cobalt content and coarser grain size of the applied tungsten carbide tool electrodes are advantageous for S-EDM.

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Publication

Reproduzierbare Optimierung des funkenerosiven Bohrens

2020 , Uhlmann, Eckart , Polte, Mitchel , Streckenbach, Jan , Osmanovic, Mirsad , Börnstein, Julian

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