Univ. Prof. Dr. Ing.

Bergs, Thomas

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  • Publication
    Discharge energy based optimisation of sinking EDM of cemented carbides
    ( 2022)
    Petersen, T.
    ;
    Küpper, Ugur
    ;
    Klink, A.
    ;
    Herrig, T.
    ;
    Bergs, Thomas
    The Electrical Discharge Machining (EDM) of cemented carbides is anticipated to enhance in order to allow more efficient machining. However, it is important that an optimisation does not deteriorate the surface integrity of the cemented carbide workpiece, since they are particularly sensitive to tensile stresses as they are caused by EDM. In order to allow for a safe optimisation, the surface integrity of every machining step has been examined before the optimisation regarding surface roughness, recast layer, heat affected zone and crack length. The same parameters have been examined for the optimised machining steps and the resulting workpiece. It was found that machining can be shortened without a significant detrimental effect.
  • Publication
    Numerical Investigation of the EDM Induced Temperature Field in a Composite Ceramic
    ( 2022)
    Hess, R.
    ;
    Olivier, M.
    ;
    Schneider, S.
    ;
    Heidemanns, L.
    ;
    Klink, A.
    ;
    Herrig, T.
    ;
    Bergs, Thomas
    The combination of high chemical and thermal durability with high hardness and strength is the main reason for the increasing use of ceramics in industry. However, these benefits lead to serious challenges for conventional manufacturing processes, which are often limited due to the mechanical properties of the workpiece material. Because of its working principle, electrical discharge machining (EDM) is almost independent from the mechanical workpiece properties. Nevertheless, the thermal loadings, which are caused by electrical discharges, result in different modifications on the surface and in sub-surface layers. These induced modifications define the surface integrity, which in turn determines the functional properties of a workpiece. Besides the intended rim zone modifications damages also occur. For a more detailed understanding of the occurring damages within the arising heat affected zone (HAZ), a heat transfer simulation for a single discharge on an alumina/zirconia/tungsten carbide ceramic was conducted in this work.
  • Publication
    Surface Integrity of Wire Electrochemical Machined Inconel 718
    ( 2022)
    Herrig, T.
    ;
    Heidemanns, L.
    ;
    Ehle, L.
    ;
    Weirich, T.E.
    ;
    Bergs, Thomas
    Wire electrochemical machining (wire ECM) combines the advantages of wire electrical discharge machining (wire EDM) and electrochemical machining (ECM). The advantages of flexible 2.5 dimensional machining without the need for an application-specific fixture are combined with the excellent surface integrity properties of the ECM. These properties make the process particularly suitable for highly critical components, like fir tree slots in turbine discs. Knowledge of the resulting surface integrity in terms of microstructure formation, oxide layers, etc. is essential for such components. Therefore, in this paper modified rim zones are investigated by wire ECM e.g. with energy filtered transmission electron microscopy.
  • Publication
    Effects of the Manufacturing Chain on the Surface Integrity when Machining Fir Tree Slots with Alternative Manufacturing Processes
    ( 2022)
    Küpper, Ugur
    ;
    Seelbach, T.
    ;
    Heidemanns, L.
    ;
    Prinz, S.
    ;
    Herrig, T.
    ;
    Bergs, Thomas
    The use of materials with increasing thermo-mechanical strengths for turbine disks and new designs inducing filigree geometries bring conventional manufacturing processes to their technical and economical limits. Investigations regarding alternative manufacturing technologies showed advantages compared to conventional broaching with high-speed steel (HSS) cutting tool material. Surface integrity is particularly crucial for the technological evaluation. However, this aspect has not been considered after downstream processes in which the machined surface integrity is modified. Therefore, the surface integrity of Inconel 718 machined by alternative manufacturing processes including wire EDM, ECM and broaching with cemented carbide is investigated after downstream processes, etching and shot peening.