Fraunhofer-Institut für Produktionsanlagen und Konstruktionstechnik IPK

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  • Publication
    Application of additive manufactured tungsten carbide-cobalt electrodes with interior flushing channels in S-EDM
    ( 2020)
    Uhlmann, Eckart
    ;
    Polte, Julian
    ;
    Bolz, Robert
    ;
    Yabroudi, Sami
    ;
    Streckenbach, Jan
    ;
    Bergmann, André
    Application fields of electrical discharge machining (EDM) are limited due to given process conditions. Manufacturing of parts with high aspect ratios and the application of multi-axis machining are limited due to process instabilities caused by removed particles. A promising approach to improve EDM process conditions, especially in sinking EDM (S-EDM), is the utilization of flushing channels in the tool electrode. However, with increasing complexity of the tool electrode geometry and the local integration of these flushing channels, conventional tool electrode manufacturing by cutting is limited. In contrast to that, the machining process selective laser melting (SLM) does not have such limitations. The appropriate integration of flushing channels, even for complex electrode geometries, improves process conditions during EDM in a variety of applications. This leads to a higher material removal rate and reduced tool wear compared to machining without flushing. Additionally, the number of required tool electrodes can be reduced, as SLM enables an efficient integration and miniaturization of all features in a single electrode. Because of its wear resistance and stability, tungsten carbide is an ideal tool electrode material, which is commonly applied in drilling EDM. After identifying suitable process parameters for roughing EDM with additively manufactured tungsten carbide cobalt tool electrodes, different forms of flushing channels were analysed in order to establish a fast process with minimum tool electrode wear. The results concerning material removal rate and the relative tool wear could be improved by applying internal flushing, though the tool wear stayed at a worse level compared to conventional tool electrode materials.
  • 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.
  • Publication
    Application of Micro Structured, Boron Doped CVD-diamond as mEDM Tool Electrodes
    ( 2018)
    Uhlmann, Eckart
    ;
    Oberschmidt, Dirk
    ;
    Bolz, Robert
    High precision cavities are used for micro injection and micro embossing tools in the field of tool making and are mainly used for small batch or mass production of micro parts. In order to fabricate a large quantity of parts, wear resistant tool materials are required. In possession of a high hardness and a high Young's Modulus, such materials are often hard or even impossible to machine by conventional fabrication processes. Being independent of the work piece's mechanical properties, Micro-Electrical Discharge Machining (mEDM) is predestined for this case. mEDM is based on the modification of state of the art process technologies and universal machine tools applied for electrical discharge machining operations [1], [2]. Besides the adjustment of the electrical parameters, the mEDM-process is also determined by the tool electrode's material which has a big influence on the material removal rate VW, the electrode's wear behavior, as well as the process results concerning surface quality and dimensional accuracy [3]. Experimental investigations aim at decreasing the wear of tool electrodes using novel electrode materials. To assure an efficient process, short production times and low tool wear TH are demanded. Therefore, electrodes with excellent electrical and thermal conductivity along with a high mechanical strength have to be used. Boron doped CVD-diamond is fulfilling these criteria. Microstructures within thin CVD-diamond foils are realized by direct structuring utilizing laser ablation and by indirect structuring using micro-structured copper substrates in the CVD-process, which transfer the micro-structure onto the growing diamond layer. Experiments were conducted in order to identify suitable EDM-parameters for different workpiece materials, namely steel 90MnCrV8, silicon carbide SiSiC and tungsten carbide K40F, which lead to lower tool wear TH and high accuracy.
  • Publication
    Manufacturing of carbide tools by Selective Laser Melting
    ( 2018)
    Uhlmann, Eckart
    ;
    Bergmann, André
    ;
    Bolz, Robert
    Application fields of electrical discharge machining (EDM) are limited due to given process conditions. When producing structures of high aspect ratios or using multi-axis machining, removed particles assemble at the machining zone, leading to process instabilities and increasing tool wear. A promising approach to improve EDM process conditions is the utilization of flushing channels in the tool electrode. However, with increasing complexity of the electrode geometry and the local integration of the mentioned flushing channels, conventional electrode manufacturing reaches its limitations. By applying Selective Laser Melting (SLM), these limitations are eliminated. An additional benefit is the efficient use of material during SLM, where nearly no waste is produced, because remaining powder can be used for the next SLM-process. The appropriate integration of flushing channels, even for complicated electrode geometries, improves process conditions during EDM in a variety of applications, leading to a higher material removal rate VW and reduced tool wear TH compared to machining without flushing. Additionally, the number of required tool electrodes can be reduced, as SLM enables an efficient integration and miniaturization of all features in a single electrode, what results in a far more sustainable process chain. Of particular interest in the field of EDM is carbide. Because of its wear resistance and stability, it is an ideal electrode material, which is commonly applied in µEDM. Tungsten carbide-cobalt is representative for this group of materials, which is already used in tool manufacturing. Several tests show a general suitability of carbide tool electrodes made by SLM for EDM-processing. However, the SLM process parameters and the composition of the carbide-cobalt show significant impact to the EDM results. A lower proportion of cobalt leads to reduced material removal rates, whereas the level of tool wear remains at a similar level. In order to benefit from the advantages of additive manufactured carbide tool electrodes, this investigation aims at decreasing waste of material and the number of required tool electrodes.
  • Publication
    Application of additive manufactured tungsten carbide tool electrodes in EDM
    ( 2018)
    Uhlmann, Eckart
    ;
    Bergmann, André
    ;
    Bolz, Robert
    ;
    Gridin, Witalij
    Application fields of electrical discharge machining (EDM) are limited due to given process conditions. When producing structures of high aspect ratios or using multi-axis machining, removed particles assemble at the machining zone, leading to process instabilities. A promising approach to improve EDM process conditions is the utilization of flushing channels in the tool electrode. However, with increasing complexity of the electrode geometry and the local integration of the mentioned flushing channels, conventional electrode manufacturing reaches its limitations. By applying Selective Laser Melting (SLM), these limitations are eliminated. The appropriate integration of flushing channels, even for complicated electrode geometries, improves process conditions during EDM in a variety of applications, leading to a higher material removal rate VW and reduced tool wear TH compared to machining without flushing. Additionally, the number of required tool electrodes can be reduced, as SLM enables an efficient integration and miniaturization of all features in a single electrode. Of particular interest in the field of EDM is carbide. Because of its wear resistance and stability, it is an ideal electrode material, which is commonly applied in mEDM. Tungsten carbide-cobalt is representative for this group of materials, which is already used in tool manufacturing. Several tests show a general suitability of carbide tool electrodes made by SLM for EDM-processing. However, the SLM process parameters and the composition of the carbide-cobalt show significant impact to the EDM results. A lower proportion of cobalt leads to reduced material removal rates VW and rising tool wear.