Now showing 1 - 10 of 52
  • Publication
    Liquid covered micro-milling
    ( 2017)
    Uhlmann, E.
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    Oberschmidt, D.
    ;
    Polte, M.
    ;
    Polte, J.
    Micro-milling tools made of cemented carbide suffer from fast tool wear and random tool breakage during the machining process. The cutting material cemented carbide is composed of a hard material phase made of tungsten carbide and a binder phase made of cobalt. An allotropical crystal lattice transformation of the binder phase at a temperature TH = 420 °C leads to increased tool wear. Commonly minimum quantity lubrication (MQL) is used as cooling lubricant technology in micro-milling. In this work a new liquid covered cooling lubricant (LCCL) technology and the commonly used MQL technology were compared regarding tool wear of cemented carbide tools for machining the steel STAVAX ESU. In the LCCL technology the cutting process is completely covered with cutting lubricant. It could be concluded that the new LCCL technology offers a high potential to reduce the tool wear in micro-milling of steel with cemented carbide micro-milling tools.
  • Publication
    Droplet removal from PVD-coated micro-milling tools with the immersed tumbling process
    ( 2017)
    Uhlmann, E.
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    Kuche, Y.
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    Oberschmidt, D.
    ;
    Polte, J.
    The physical vapour deposition (PVD) process is widely used for the coating of cutting tools. The increased hardness and temperature stability permitted a higher cutting speed and longer tool life in comparison to uncoated tools. Within the PVD-process droplets of the target can be deposited on the coated surface. The consequence is an inhomogeneous surface of the cutting tools with an increased surface roughness. In this study, the immersed tumbling process is used for the droplet removal of micro-milling tools. The results show the functionality of the process for the droplet removal depending of the lapping media and process parameters in connection with the amount and size of the droplets.
  • Publication
    Wear behaviour of diamond coated micro-milling tools during micro machining
    ( 2017)
    Uhlmann, E.
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    Kuche, Y.
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    Oberschmidt, D.
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    Polte, J.
    Graphite electrodes are used in the die sinking process for manufacturing of micro structured tools in the die and mould fabrication. They are machined using the micro-milling process. During the cutting process graphite grains have strong abrasive effects on the cutting edges and lead to high tool wear. Consequences are short path length lc and geometrical errors. One approach to reduce tool wear is the tool coating with diamond. The diamond coating changes the cutting edge micro geometry which has influences on the process behaviour. In this paper, the wear behaviour of micro-milling tools with diameter D = 0.5 mm and different micro geometries is analysed and discussed. The results show better wear behaviour for prepared and coated tools.
  • Publication
    Low-dimensional time-discrete models for high dynamic machine tools
    ( 2017)
    Uhlmann, E.
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    Reis, T.
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    Oberschmidt, D.
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    Rendel, O.
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    Guhde, S.
    The coupling of real and virtual machine tool components in a hardware-in-the-loop environment is commonly used by state-of-the-art engineering tools as well as automated test procedures to verify the system behaviour. Time deterministic models are necessary to provide simulation results in a predictable time frame. This leads to efficient development procedures. This article presents a method and results of an automated engineering tool that uses time discrete deterministic order-reduced systems for the calculation of the dynamic machine tool behaviour. An innovative model-order-reduction (MOR) procedure was developed that provides a low-dimensional approximation of the original model with associated error estimation as well as inherent system characteristics, like passivity and steady-state accuracy, for a defined time step width. The validation of the calculation model, based on the new MOR procedure, was carried out on a three-axes test stand. It is representative f or high dynamic machine tools and equipped with an integrated real-time control environment. The real-time settings as well as stiffness K, damping D, and mass M can be adjusted. Various low-dimensional time discrete models were implemented for demonstrative application and experimental validation of the MOR procedure. The results show high potential for the use in engineering processes. A reduction from a secondary order system with 19, 932 unknowns to a first order system with 80 unknowns was realized. Furthermore, the difference between calculated and measured deviation of the test stand's x-axes was achieved with a value of eXMax = 750 nm.
  • Publication
    Measurement of in-mould shear rates by x-ray particle image velocimetry
    ( 2017)
    Uhlmann, E.
    ;
    Hein, C.
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    Oberschmidt, D.
    The manufacturing of large quantities of polymeric optical and micro-optical components becomes more and more important regarding industrial applications as MEMS devices, customer electronics or micro imaging systems. The relevant parameters for the qualification of polymeric micro optics as surface roughness, shape and positional tolerances, refractive index, molecular orientation, injection moulding process induced deviations and their connection to injection moulding parameters are largely known. The manufacturing of micro optics by micro injection moulding and associated with that, micro injection moulding machine tools with highly complex plastification and injection systems is far less understood. In particular, the influence of shear loads and temperature deviation on replication quality has not been fully investigated. The occurring shear rates during injection moulding lead to mechanical damage of the polymer on a molecular level and reduced optical functionality. This work presents an approach for in mould shear rate measurement by the use of a metrological computed tomography system. Using metal powder with a particle size 3 mm < dp < 5 mm as tracer particles, Polyetheretherketon (PEEK) as mould material, a Zeiss Metrotom 800 computer tomography system and a Babyplast injection unit, streamlines of polymer flow could be visualized. In accordance to optical particle image velocimetry (PIV), for each frame a matrix including particle position was calculated. The temporal shift of these positions lead to velocity gradients that allow the calculation of shear-rates . By reproducing relevant elements of injection units and mould structures, this works enables the profound investigation of fluid dynamics regarding micro injection moulding and the correlation between shear loads and polymer characteristics.
  • Publication
    Cutting forces while machining STAVAX ESU with binderless-cBN
    ( 2017)
    Uhlmann, E.
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    Oberschmidt, D.
    ;
    Polte, J.
    ;
    Polte, M.
    Binderless-cubic-Boron-Nitride(cBN) from the company SUMITOMO CORPORATION, Itami, Japan, provides the opportunity for direct cutting of steel with ultra-precision quality without additional equipment or coating of the workpiece. This work presents the latest results in the field of ultra-precision machining of hardened stainless steel with binderless-cBN. In this paper the influence of the cutting speed vc, the feed f, the depth of cut ap, and the cooling lubricant on the cutting force Fc is shown for turning the stainless steel STAVAX ESU. The cutting speed, the feed and the depth of cut were varied between 3 m/min < vc < 450 m/min, 0.9 mm < f < 9.7 mm, and 5 mm < ap < 30 mm respectively. As cooling lubricants compressed air and W200SL of the company OPORTET, Duisburg, Germany, with a volumetric flow rate & = 1 l/min were used. For measuring the cutting forces Fc the piezoelectric dynamometer MINIDYN 9256C2 from the KISTLER INSTRUMENTE AG, Middlefield, USA, was used. As a result of this work cutting forces Fc < 4.9 N could be observed with an inconstant progression over the varied process parameters.
  • Publication
    Manufacturing of CVD diamond micro-end mills with electrical discharge machining
    ( 2017)
    Uhlmann, E.
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    Oberschmidt, D.
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    Polte, M.
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    Polte, J.
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    Schimmelpfennig, T.-M.
    ;
    Börnstein, J.
    At state of the art micro-milling tools made of cemented carbide are widely used in industry. Nevertheless, these micro-milling tools suffer from fast and random tool breakage while cutting. To improve the wear behaviour of micro-milling tools new cutting materials have to be established. In this work electrical discharge machining (EDM) for manufacturing of micro-milling tools with cutting edges made of boron doped chemical vapour deposition (bdCVD) diamond were investigated. Wire-EDM and die-sinking-EDM were compared regarding the characteristics of the micro-tool´s cutting edges. It could be concluded that the wire-EDM process is suitable for manufacturing of micro-milling tools with cutting edges made of bdCVD diamond. With respect to the elaborated technologies for the wire-EDM process a cutting edge radius rv = 3.9 mm and for the die-sinking-EDM process a cutting edge radius rv = 5.4 mm could be measured.
  • Publication
    Effects of different cutting edge preparation methods on micro milling performance
    ( 2016)
    Uhlmann, E.
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    Oberschmidt, D.
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    Kuche, Y.
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    Löwenstein, A.
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    Winker, I.
    In micro milling, which is mostly used in mold and die making, process reliability and predictability of tool failure are important. Particularly in precision and micro machining, tool breakage is hardly detectable and the requirements on accuracy are very high. Immersed tumbling is an appropriate process for the defined cutting edge preparation of micro milling tools. Its effects like increasing tool wear performance and tool life has been evaluated. In this paper, different cutting edge preparation processes showed that in cutting tests different effects occur regarding tool wear, process forces and surface quality. Immersed tumbling leads to the lowest active force Fa, but magnet finishing leads still do a slightly better surface quality.
  • Publication
    Effect of cooling lubricant on surface roughness for turning stainless steel with binderless-cBN
    ( 2016)
    Uhlmann, E.
    ;
    Oberschmidt, D.
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    Polte, J.
    ;
    Polte, M.
    ;
    Huth-Herms, K.
    Binderless-cubic Boron Nitride (cBN) from the company SUMITOMO CORPORATION, Itami, Japan, is one of the most promising cutting materials providing the opportunity for direct cutting of steel with ultra-precision (UP) quality without additional equipment or coating of the workpiece. This work presents the latest development in the field of precision machining of hardened stainless steel with binderless-cBN. In this paper the influence of the feed f and the cooling lubricant on the surface roughness is shown for turning the hardened stainless steel STAVAX ESR (H = 52 HRC) from the company BÖHLER-UDDEHOLM, Düsseldorf, Germany. A surface roughness Ra = 9 nm and Rz = 42 nm could be achieved using binderless-cBN and the cooling lubricant W200SL of the company OPORTET, Duisburg, Germany.
  • Publication
    High precision milling with a novel compliant machine tool
    ( 2016)
    Uhlmann, E.
    ;
    Oberschmidt, D.
    ;
    Guhde, S.
    ;
    Polte, M.
    For precision milling manufacturing machine tools with high stiffness K and high masses m are state of the art. Usually this will be achieved due to heavy and large machine beds and frames. Hence, a new approach based on the compensation of the dynamic dislocation was investigated. The aim of this new approach was to develop a high dynamic machine tool with a compliant machine frame. Therefore, a novel compliant three- Axes machine tool for high precision milling based on an Ethercat Technology® and the open source ethercat master etherlab machine is developed by the Technische Universität Berlin and the Fraunhofer Institute for Production Systems and Design Technology. For the dynamic dislocation a Kalman-filter is integrated in the machine control which calculates the tool body with respect to the tool-center-point TCP and its velocity v. For the verification milling structures are manufactured with the compliant machine tool.