Now showing 1 - 10 of 16
  • Publication
    Application of laser surface nanotexturing for the reduction of peri-implantitis on biomedical grade 5 Ti-6Al-4V dental abutments
    ( 2019)
    Uhlmann, E.
    ;
    Schweitzer, L.
    ;
    Cunha, A.
    ;
    Polte, J.
    ;
    Huth-Herms, K.
    ;
    Kieburg, H.
    ;
    Hesse, B.
    The annual revenue of dental implants is estimated on 33 billion USD in 2019 and the efforts to keep the teeth functionality and aesthetics is continuously growing over the years. However, loosening of dental implants induced by infection is still a critical and common problem worldwide. In this scenario, the development of new implant manufacturing strategies is of utmost importance. Every surface exposed in the oral cavity, both the tooth and the implant surface, are covered by a layer of salivary proteins, the so-called pellicle. The initial formation of a pellicle is followed by the attachment of bacterial cells onto it. Well-developed biofilms on dental implant surfaces become the main source of pathogenic microbes causing Peri-Implantitis, which is one of the main causes of dental implant failure. The surface topography and chemical composition of an implant are key factors in controlling surface wettability, which directly affects the formation of the biological films. In this sense, ultrafast laser surface nanotexturing rises as a promising advanced technology for controlling implant surface biological properties. Laser-processing parameters such as laser wavelength l, fluence F and number of pulses N are essential for surface texturing. Thus, this paper presents promising results on the influence of different laser induced periodic surface structures (LIPSS) on the composition of the pellicle and the biofilm formation on biomedical grade 5 Ti-6Al-4V dental abutments. Moreover, a biofilm reactor was built and adapted to assess the effect of the LIPSS on the biofilm formation.
  • Publication
    Cutting force prediction in micro-milling considering the cutting edge micro-geometry
    ( 2019)
    Uhlmann, E.
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    Polte, J.
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    Wiesner, H.M.
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    Kuche, Y.
    ;
    Polte, M.
    The micro-milling process is used for a wide range of materials and enables the manufacturing of complex geometries with micro-features. One important factor for the tool life is the cutting force Fc, which depends on the applied technology, process parameters and cutting edge micro-geometry. High cutting forces Fc can lead to tool breakage in the transition between the shank and the cutting part of cemented carbide end mills. The prediction of cutting forces Fc in micro-milling processes through cutting force models could potentially decrease the hazard of tool breakage. By including the cutting edge radius rv into the prediction model, additional correction factors can be avoided. Therefore, further knowledge about the applicability of those models for the micro-milling process with chip thickness h < 0.01 mm is needed. In this investigation, the cutting force model of KOTSCHENREUTHER [1], which takes the cutting edge radius rv into account is used for the cutting force prediction in micro-milling. In order to validate this model, an innovative lead free copper alloy CuZn21Si3P is machined. Cemented carbide micro-milling tools with tool diameter D = 1 mm were used. The manufacturing of different cutting edge radii rv was realised with the immersed tumbling process. During milling experiments with a five-axis high precision machine tool the cutting forces Fc were measured. Cutting forces in a range of 6 N < Fc < 26 N were detected. The results show good correlations between the predicted and experimental determined cutting forces Fc. Furthermore, the measured cutting edge radii rv show a high influence on the deviation of the measured and predicted cutting forces Fc.
  • Publication
    Micro-cutting of a MMC-composite for enhanced injection moulds
    ( 2019)
    Uhlmann, E.
    ;
    Polte, M.
    ;
    Hein, C.
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    Polte, J.
    ;
    Jahnke, C.
    Tools for micro-injection moulding are currently made of hardened steel. These tools are exposed to high local loads, which significantly reduce the injection moulding tool life time tT. Furthermore, the occurring wear of the milling tool during machining of hardened steel leads to reduced surface roughness Ra and geometrical accuracy GF. Copper and aluminium alloys as mould materials provide an alternative to hardened steel with advantages regarding material removal rate QW and wear of the milling tool, but with a significantly reduced life time of the injection moulding tool tT. Until now, the combination of a good machinability and high wear resistance cannot be achieved. The approach, presented in this paper consists of an easy to machine material and the development of a wear resistant metal-matrix-composite (MMC) material layer with a hardness of up to 3,000 HV. Therefore, the pre-machined test specimens made of aluminium-bronze are coated by laser dispersing with wolfram-carbide-particles W2C-WC. Furthermore, for the finishing machining of the coated moulds, a cutting technology for the machining of W2C-WC-particles was developed. The verification of the developed technology was performed with an injection moulding process based on carbon-fibre reinforced thermoplastic material. By means of documented machining efforts, the quality indicators geometrical accuracy GF and surface roughness Ra as well as occurring tool wear, the feasibility of the developed technology was demonstrated.
  • Publication
    Mikrofräsbearbeitung von MMC-Werkstoffschichten unter Einsatz von binderlosem PKD. Analyse des Einflusses der Prozessparameter auf den Mikrofräsprozess
    ( 2019)
    Hein, C.
    ;
    Uhlmann, E.
    ;
    Polte, J.
    ;
    Wiesner, H.M.
    ;
    Jahnke, C.
    ;
    Polte, M.
    Micro-injection moulding is a key technology for the cost-effective production of plastic parts. The commonly used moulds are made of hardened steel and machined by micro-milling with coated cemented carbide tools. Today, these tools suffer from random tool breakage and excessive wear. One solution of this problem is to produce injection moulds made of non-ferrous metals and enhance them by applying a tungsten carbide matrix on the surface. Thus, this investigation addresses the micro-milling process of the resulting Metal-Matrix-Composites. Furthermore, the feasibility of binderless polycrystalline diamond as an innovative cutting material could be shown for this purpose
  • Publication
    Manufacturing of graphite electrodes with high geometrical requirements
    ( 2019)
    Uhlmann, E.
    ;
    Kuche, Y.
    ;
    Polte, J.
    ;
    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
    Die-sinking EDM of a SiC-boride-composite
    ( 2019)
    Uhlmann, E.
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    Polte, J.
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    Jahnke, C.
    ;
    Wolf, C.-S.
    ;
    Degenhardt, U.
    Silicon carbide-based composites are highly demanded for industrial applications, like heat exchangers in corrosive environments. In consequence of the mechanical properties like high hardness H and brittleness, cutting processes are still challenging. An opportunity for processing difficult-to-cut materials with sufficient electrical conductivity s is electrical discharge machining (EDM). In order to develop suitable machining technologies, known parameters for common material combinations can serve as a starting point. Hence, standard technologies from the database of a commercial die-sinking EDM machine tool were applied for machining a silicon carbide-boride-composite. The material removal rate QW and the arithmetical mean deviation Ra for finishing and roughing operations are observed. The formation of cracks and the extend of the typical deposition layer formed at the surface of the workpiece is analysed through scanning electron microscopy. While the material removal rate QW is increasing with higher discharge energies W in this investigation, the arithmetical mean deviation Ra is not dependent on this property. Furthermore, spalling is identified as main material removal mechanism occurring in this process. Overall, the machinability of silicon carbide-boride composites with EDM, applying commercial available parameter technologies, is successfully demonstrated.
  • Publication
    Mikrofräswerkzeuge mit Schneiden aus cBN
    ( 2018)
    Uhlmann, E.
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    Polte, J.
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    Polte, M.
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    Kuche, Y.
    ;
    Wiesner, H.
    Die Mikrozerspanung ist eine Kerntechnologie bei der Fertigung von Mikrospritzgussformen. Die hohen Ansprüche an die geometrische Genauigkeit und Oberflächenrauheit erfordern den Einsatz hochfester Werkstoffe. Jedoch unterliegen aktuelle Fräswerkzeuge bei der Mikrozerspanung einem hohen Verschleiß. Einen Lösungsansatz bietet der erfolgreich in der Makrozerspanung eingesetzte Schneidstoff kubisch-kristallinesBornitrid(cBN). Ziel der Untersuchungen war es daher, detaillierte Informationen zur Bearbeitung von gehärtetem Stahl mit cBN-Mikrofräswerkzeugen bereitstellen zu können.
  • Publication
    Wear behaviour of diamond coated micro-milling tools during micro machining
    ( 2017)
    Uhlmann, E.
    ;
    Kuche, Y.
    ;
    Oberschmidt, D.
    ;
    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
    Droplet removal from PVD-coated micro-milling tools with the immersed tumbling process
    ( 2017)
    Uhlmann, E.
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    Kuche, Y.
    ;
    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
    Liquid covered micro-milling
    ( 2017)
    Uhlmann, E.
    ;
    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.