Now showing 1 - 10 of 19
  • Publication
    3-Achs-Portalfräsmaschine als Demonstrator für ein modulares Werkzeugmaschinengestell
    ( 2019)
    Uhlmann, E.
    ;
    Polte, M.
    ;
    Blumberg, J.
    ;
    Peukert, B.
  • 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
    Ultra-precision-milling of silicon by means of single crystal diamond tools
    ( 2019)
    Uhlmann, E.
    ;
    Polte, M.
    ;
    Rolon, D.A.
    ;
    Kühne, S.
    Silicon is an important material often employed on most of micro-electro mechanical systems (MEMS), integrated circuits, micro-chips, and micro-fluidic devices. Therefore, strategies and process parameters to machine those planar 2.5-D geometries of silicon are essential. Moreover, silicon belongs to the group of hard-brittle materials, which means that it is very likely to originate cracks during the milling operations as a result of the intermittent interaction of the cutting edge and the silicon surface. Besides, the machining of silicon results on severe tool wear. The ductile-brittle transition and tool wear reduction of the silicon-milling are aspects still not completely investigated. Consequently, this paper aims at finding the proper parameter range for ductile ultra-precision milling (UP-milling) of 2.5-D silicon geometries employing single crystal diamond cutting tools. Furthermore,the evaluation the tool wear after the process is a crucial part of the investigations. In order to fulfil such knowledge gap, single groove experiments are proposed. The milling process to generate those grooves is monitored by means of force measurements. Also, surface aspects of the machined grooves are measured through white light interferometry (WLI). For evaluating tool wear, dry UP-milling investigations are conducted and images of the cutting edges are taken by means of a scanning electron microscope (SEM). The experiments show that the machining of silicon is feasible and the ductile material removal is possible. Moreover, the process forces Fpr generated by the UP-milling process of single crystal silicon are able to be employed for monitoring and avoid the transition from ductile to brittle material removal.
  • 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
    Investigation on the effect of novel cutting fluids with modified ingredients regarding the long-term resistance of polycarbonate used as machine guards in cutting operations (KSS-PC)
    ( 2019)
    Uhlmann, E.
    ;
    Haberbosch, K.
    ;
    Thom, S.
    ;
    Drieux, S.
    ;
    Schwarze, A.
    ;
    Polte, M.
    Machine guard enclosures prevent the accessibility of hazard zones and safeguard against ejection of parts during operation, such as chips, tool and workpiece fragments as well as cutting fluids (DGUV 2008, DIN EN 12417). Vision panels as part of machine tool enclosures allow the observation of the machining process. Due to its high ductility, impact resistance Y and its optical properties, polycarbonate is the primarily used material for machine guard windows (Uhlmann and Duchstein 2008, Uhlmann and Duchstein 2010). By influence of cutting fluids, chip impact, ultraviolet radiation and heat, polycarbonate underlies a reduction of long-term resistance, which is called aging. In order to improve the protection of human health and environment, the European Union adopted the regulation ""Registration, Evaluation, Authorization and Restriction of Chemicals"" (REACH) in 2007. The implementation of REACH leads to modified cutting fluids, which need to be analyzed regarding their effect on long-term resistance of polycarbonate. This is important due to a not yet verified suspicion that cutting fluids with increased alkalinity, use of solvents, such as phenoxyethanol, or application of amines, such as dicylohexylamine, might increase aging of polycarbonate. Two approaches are presented in this paper. First, a qualitative approach is proposed to compare cutting fluids by determination of resistance of environmental stress cracking. Secondly, the effect of three cutting fluids on the long-term resistance in a quantitative way is presented. Aging of the polycarbonate is carried out by a time-controlled exposition with cutting fluid and under defined conditions over ten weeks. Impact resistance Y is determined by impact tests. Material properties are measured by tensile tests.
  • 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.