Univ. Prof. Dr. Ing.

Bergs, Thomas

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  • Publication
    Optimum cutting strategy for machining of particle reinforced AlMC
    ( 2006)
    Klocke, Fritz
    ;
    Bergs, Thomas
    ;
    Kusumah, Indra
    The machining experiments are accomplished exemplarily on the machining of SiC particle reinforced sintered AlMC (Aluminium Matrix Composites). A special emphasis is put thereby on the analysis of the cutting process, whereby in particular the material separation mechanisms are investigated. For a fundamental and comprehensive research of the cutting process the most important influence collective, which arises during the machining, is considered. There are three main influencing factors, namely material composition of AlMC, cutting tool and machining parameter. The main objective is to find the optimum cutting strategy with a high cutting rate and at the same time a low wear rate. As concluded in chapter 3.3. that there is an optimum process temperature during cutting of MMC which is reached by using the right combination of cutting velocity and feed rate. By taking all relevant aspects into account a conclusion for an optimum cutting strategy of particle reinforced AlMC can be taken as the following: Abrasive wear is the most influencing wear mechanism on machining of AlMC; The matrix material aluminium defines the main factor on optimum process temperature, because the melting point of aluminium (660 deg C) is much lower than melting point of SiC particle (2700 deg C). When the material is getting soft the tool wear rate will be decreasing; Increase of SiC particle content will increase the tool wear with the multiplication factor of 2; The best cutting performance is achieved by cutting tool coated with TiAlN and by using minimum quantity lubrication; A big tool nose radius 0,5 mm and rake angle 14 deg lead to a longer tool life. The best cutting parameters are: feed per tooth = 0,1 mm/tooth and cutting velocity = 500 m/min. These parameters are suggested for the gut compromise between the expected high cutting rate and low wear rate. Entnommen aus TEMA
  • Publication
    Appointing subsurface material properties of Ti6242 and Udimet720 by high speed 5-axis machining
    ( 2006)
    Klocke, Fritz
    ;
    Albrecht, J.
    ;
    Bergs, Thomas
    ;
    Meinecke, Matthias
    ;
    Rohde, L.
    In this paper the complex dependencies between machining parameters and resulting properties for a typical multi-step process consisting of roughing, pre-finishing and finishing operations are discussed. First the machinability is analyzed through simulation and analogy tests due to fundamental phenomena such as chip geometry and the material specific influence on chip formation. Secondly parameter windows for each of the different process steps are defined. During the finish milling process cutting velocities of up to 400 m/min for Ti6242 and 150 m/min for Udimet 720 LI are tested. To evaluate the different process parameters, forces are experimentally measured and the wear behavior is analyzed. Subsurface material properties are directly affecting the service performance of thermo-mechanically highly loaded parts such as aero engine components. For this purpose, surface processes subsequent to machining operations are conducted to induce a beneficial state of residual stresses. The paper on hand investigates material properties of technical surfaces that have been machined with parameter sets characterized by high cutting velocities v(ind.c) = 100 m/min to 400 m/min for Ti6242 and v(ind.c) = 50 m/min to 150 m/min for Udimet 720 LI. Therefore, different tool geometries have been tested with regards to maximum tool life at optimized material removal rates. The resulting characteristics of the surfaces may give practical support for process planners to design their process chain. With the correlations presented in this paper the first step to a comprehensive understanding of the dependencies between high speed machining and a component's properties is achieved. Entnommen aus TEMA