Now showing 1 - 10 of 11
  • Publication
    Cutting force prediction in micro-milling considering the cutting edge micro-geometry
    ( 2019)
    Uhlmann, E.
    ;
    Polte, J.
    ;
    Wiesner, H.M.
    ;
    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.
    ;
    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
    Mikrofräswerkzeuge mit Schneiden aus cBN
    ( 2018)
    Uhlmann, E.
    ;
    Polte, J.
    ;
    Polte, M.
    ;
    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
    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.
  • Publication
    Cutting forces while machining STAVAX ESU with binderless-cBN
    ( 2017)
    Uhlmann, E.
    ;
    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.
    ;
    Oberschmidt, D.
    ;
    Polte, M.
    ;
    Polte, J.
    ;
    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
    Effect of cooling lubricant on surface roughness for turning stainless steel with binderless-cBN
    ( 2016)
    Uhlmann, E.
    ;
    Oberschmidt, D.
    ;
    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
    CBN-micro-milling tools for machining hardened steel moulds
    ( 2016)
    Uhlmann, E.
    ;
    Oberschmidt, D.
    ;
    Polte, M.
    ;
    Polte, J.
    ;
    Börnstein, J.
    High-precision cutting of hardened steel with geometrical defined cutting edge is restricted due to excessive and random tool wear. For serial production of precision plastic parts hot embossing tools and micro injection moulding tools with high requirements regarding geometrical accuracy and surface roughness are needed. Cutting materials based on cubic Boron Nitride (cBN) are successfully used in macro-machining of hardened steel. In this paper, detailed information about machining hardened steel with micro-milling tools with cutting edges made of cBN are given. An arithmetical mean deviation Ra = 19 nm could be achieved using a high-precision micro-milling machine tool with ball bearing guideways and spindle.