Fraunhofer-Institut für Produktionsanlagen und Konstruktionstechnik IPK

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  • Publication
    Scaling of the milling process of tungsten-copper-composites
    ( 2007)
    Uhlmann, E.
    ;
    Graf von der Schulenburg, M.
    This article deals with the experimental and numerical research of scaling effects occurring in the milling process of tungsten-copper-composites (WCu). The experimental tests served to quantify single scaling effects like e.g. milling cutter diameter and the feed per tooth. To enhance the understanding of the process the effects were emulated numerically with finite element simulations. In all experiments an intense impact of the specific WCu material properties on the machining process and the quality of the process output was detectable. The tests concerning the tool displacement showed that an enlargement of the feed per tooth causes a significant increase of the tool displacement and also that a smaller mass fraction of tungsten promotes a smaller tool displacement, however at the cost of higher data scattering. A high tungsten mass fraction impedes the chip formation and leads to intense tool deformations due to the hardness of tungsten. The preliminary quasistatic chipping tests validated that a lower tungsten mass fraction leads to decreasing cutting forces. The increasing cutting forces coming along with smaller tungsten particle size correlated with milling experiment executed previously but were only detected with WCu 60/40 so far. The SEM pictures show clear differences between the WCu specifications and support the high impact of the WCu material characteristics. A thermographic test setup was developed to obtain knowledge about the temperatures at the tip of the cutting edge of a milling tool. The tests pointed out that the temperature rises during the engagement time whereas most of the cooling happens in the first quarter of the idle time. Since the previous 3D model used for FEM simulations did not provide a constant element size in the model for different WCu specifications a new fully parameterized geometry preprocessor was programmed. First simulations confirmed the strong influence of the WCu specifications on the process outcome. Entnommen aus TEMA
  • Publication
    Entwicklung eines Bearbeitungszentrums zur Mikrofertigung durch Fräsen und Laserabtrag
    ( 2007)
    Eßmann, J.
    In der Feinwerktechnik, bei der Herstellung medizin- und biotechnischer Produkte sowie im Werkzeug- und Formenbau werden Strukturen kleinster Abmaße und hoher Oberflächengüten erzeugt. Die Kombination aus 5-Achs-Mikrofräsbearbeitung und Lasermaterialabtrag mittels gepulster Laserstrahlung sowie die Erfassung der Werkstückgeometrie im Arbeitsraum bietet eine Alternative zu etablierten Fertigungsprozessketten wie beispielsweise der Formherstellung mittels Funkenerosion (EDM). Im Rahmen des Vorhabens HiDynMolder wird eine Werkzeugmaschine zur Mikrofertigung durch Fräsen und Lasermaterialabtrag entwickelt. Die Kombination dieser Fertigungsverfahren mit der maschinenintegrierten Werkstück-Geometrieerfassung stellt eine flexible Alternative zu etablierten Prozessketten der Mikrofertigung dar. Insbesondere Werkzeuge und Formen aus gehärteten Stahlwerkstoffen können durch eine hochdynamische Fräsbearbeitung mit Ultrafeinstkorn-Hartmetallwerkzeugen und Lasermaterialabtrag mittels Kurzpuls-UV-Laserstrahlung wirtschaftlich hergestellt werden. Dazu wird das Bearbeitungszentrum mit einer Schlichtspindel ausgerüstet, die eine maximale Drehzahl von 250.000 min(exp -1) erreicht sowie mit linearmotorgetriebenen Maschinenachsen, die einen Ruck oberhalb 1000 m/s(exp 3) ermöglichen. Die berührungslose Geometrieerfassung ermöglicht eine Nachbearbeitung ohne Umspannverluste, die auf der Basis der tatsächlich vorhandenen Bauteilgeometrie geplant werden kann. Der Lasermaterialabtrag stellt dabei eine wirtschaftliche Erweiterung im Bezug auf minimale Strukturabmaße, Geometriekomplexität und Werkstoffspektrum dar. Entnommen aus TEMA
  • Publication
    Optimizing the feed velocity of NC-tool paths
    ( 2007)
    Uhlmann, E.
    ;
    Mattes, A.
    In recent years various simulation tools with which the feed velocity can be optimized have been developed for an efficient milling of complex components. Hitherto, the material removal rate has been calculated and the respective commands in the NC-program have been adapted. Further approaches include the mechanical tool load which is determined analytically. Equally, the material removal rate has a significant influence on the thermal tool load. This paper describes an approach with which both the mechanical as well as the thermal load is calculated for a given NC-tool path. If a certain value is overstepped, the feed velocity is reduced respectively. As a result the feed velocity is optimally adjusted to the engagement conditions. In addition, the calculation of the wear is carried out. In cutting experiments with Ck45 and Inconef718 it was possible to reduce the primary processing time significantly. Furthermore, regarding Ck45 it was possible to predict the wear with a small fault tolerance. Concerning that NC-speed already assures a maximum economy of time for machining of 20 % compared to a not optimized NC-Code, this clarifies the achieved results. Against this background it seems not negative at all, that the tool wear is not reduced through the integration of technology inside the optimization, Furthermore it has to be stated positively that the tool wear does not rise despite the significant decreased machining time. Another objective of the cutting experiment was the verification of the calculated tool wear with the measured one. It may declared, that the results are in good agreement for the fourth and the fifth section of the cutting edge. However, generally the cutting experiment shows that a prediction of the tool wear is possible with a sufficient accuracy for deciding if a tool change is necessary or not. Thus the achieved benefit may help to improve the process reliability and reduce the tool costs. Entnommen aus TEMA
  • Publication
    Investigations on the adjustment of the modeling section in 2D simulation of milling processes
    ( 2007)
    Uhlmann, E.
    ;
    Mattes, A.
    ;
    Zettier, R.
    ;
    Graf von der Schulenburg, M.
    Conducting 3D simulation of milling processes still causes high efforts. There, only small workpiece sections can be modeled so far, instead of the entire contact width. Approaches using 2D simulation pose an interesting alternative. Here, the two-dimensional perspective is gained by dividing the workpiece into different sections perpendicular to the feed rate. This, however, requires a modeling approach that covers arbitrary contact widths along with a high mesh density in the area of chip formation. Automatically adjusting the modeling section hereby helps to model contact width up to 180 deg by segmentally simulating the rotation of the milling cutter. The paper presents the investigations on the effect of the most important parameters which influence sufficiently accurate computation of the equivalent cutting forces as in conventional 2D simulation models using the software DEFORM 2D. The operational reliability of the model was verified by a newly conducted simulation conducted using the new simulation model, with which the points in time of the adjustments for a model section were not recognizable at the cutting force distribution. In addition a realistic cutting force plot for milling operation was realised and the stress occurring at the end of a workpiece section could be held on a constant level. Undesired variations compared to simulations without adjustment of the modelling sections were limited on an area behind the tip of the cutting wedge. There, risings in stress occur inside the workpiece after modifications of the model. An influence on the cutting force however was not observable. Thus, the new simulation model accomplishes the requirements for the simulation of long cutting distances at reduced computing time. However, further studies will have to show, how applicable these results are for other simulation parameters. Entnommen aus TEMA
  • Publication
    Simulation zur Prozeßoptimierung
    ( 1990)
    Potthast, A.
    Mit der grafischen Simulation der NC-Programme wird die Überprüfung des Bearbeitungsablaufs vor dem erstmaligen Produzieren eines Werkstückes auf der Maschine ermöglicht. So sollen Fehler bereits währed des Simulationslaufes erkannt und das Einfahren und Testen neu erstellter Programme von der Maschine auf den Bildschirm verlagert werden. Am Bildschirm wird aus dem Rohteil das Fertigteil produziert. Die Verfahrbewegung sowie der Eingriff des Werkzeuges am Werkstück müssen dabei kontrolliert und Ablauffehler erkannt werden. Als Basis einer universellen Darstellung der Geometrie von Werkstück, Spannmittel und Werkzeug im Hinblick auf eine rechnerische Kollisionskontrolle ist ein 3D-Volumenmodell erforderlich. Die Simulation des Bearbeitungsablaufes soll echtzeitnah erfolgen, um auch die programmierten Vorschübe visuell überprüfen zu können. Die am IPK entwickelte "Grafisch-dynamische Simulation der Bohr- und Fräsbearbeitung" sowie "Grafisch-dynamische Simulation der Doppelschlittendrehbe arbeitung" bieten die aufgezählten technischen Merkmale sowie weitergehende Systemlösungen, die die Integration der Simulationssysteme in ein durchgängiges CIM-Konzept ermöglichen.