Univ. Prof. Dr. Ing.

Bergs, Thomas

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  • Publication
    Empirical Modeling of Abrasive Waterjet Process for Controlled Depth Machining of Dense Segmented Ceramic Thermal Barrier Coatings
    ( 2021)
    Borrmann, Jan Philipp
    ;
    Dadgar, Mohammad
    ;
    Döring, Jens-Erich
    ;
    Herrig, Tim
    ;
    Bergs, Thomas
    Abrasive waterjet (AWJ) controlled depth machining shows promise to be one of the most efficient non-conventional structuring techniques for dense segmented Thermal Barrier Coatings (STBC) on turbomachinery hot gas components made of Yttria-Stabilized Zirconia. Exemplary applications in the field of gas turbine technology are engraving of structures to optimize gas turbine performance and the stripping process of TBC within the repair process chain. As there are no comprehensive process models available, the development of an appropriate AWJ machining process is demanding. Thus, deeper process understanding and modeling need to be investigated. This paper shows an empirical modeling of AWJ process for controlled depth machining of dense segmented TBC material. The practical trials are based on a Design of Experiments (DoE). The investigated influencing parameters are water pressure, abrasive mass flow, feed rate, hatch distance and machining angle. The considered target variables are ablation depth and surface roughness. Furthermore, the process stability is investigated. The developed empirical model results in an acceleration of process parameter determinations.
  • Publication
    Experimental investigation of abrasive properties in waterjet machining
    ( 2021)
    Schüler, Manuel
    ;
    Dadgar, Mohammad
    ;
    Herrig, Tim
    ;
    Klink, Andreas
    ;
    Bergs, Thomas
    Abrasive waterjet (AWJ) machining has proven to be one of the most flexible non-conventional production techniques for difficult-to-machine materials. However, the prediction of process results is challenging since multiple physical processes occur simultaneously. Until now, the use of alternative abrasive material for special applications has received limited attention. In this work, different solid materials of altered shape and mechanical properties were used to analyze the physical phenomena experimentally. A ceramic and a steel abrasive material of either circular or angular geometry were used. The experiments were conducted by AWJ controlled-depth machining on 42CrMo4 steel in various structural modifications regarding the interference of particle interactions. Furthermore the study aims to gain a fundamental understanding of the AWJ erosion process of different abrasive grit for a better prediction and optimization of AWJ machining, in particular for future applications.
  • Publication
    Automotive hybrid design production and effective end machining by novel abrasive waterjet technique
    ( 2021)
    Schüler, Manuel
    ;
    Heidrich, Daniel
    ;
    Herrig, Tim
    ;
    Fang, Xiangfan
    ;
    Bergs, Thomas
    Hybrid designs with the combination of metal and long fiber reinforced thermoplastics (LFT) offer a great opportunity to reduce component weight for automotive applications. Production costs are typically high due to complex processes and challenging end machining. A complete manufacturing process chain for simultaneous hybrid design production is presented. Hybrid forming, a manufacturing process combining metal sheet forming, LFT compression molding and bonding, was developed to manufacture an automotive lightweight component, finally end machined by innovative waterjet techniques. Besides optimizing waterjet end machining strategies, waterjet controlled-depth machining was used to remove LFT material selectively, resulting in increased hybrid production flexibility.
  • Publication
    An Improved Model for Contour Damage Compensation in 3D Waterjet Machining
    ( 2021)
    Dadgar, Mohammad
    ;
    Schreiner, Thorsten
    ;
    Schüler, Manuel
    ;
    Herrig, Tim
    ;
    Bergs, Thomas
    Waterjet machining is a particularly flexible and powerful tool for processing of high-performance materials which are difficult to machine conventionally. Waterjet cutting is a non-conventional and time efficient cutting technique without any significant thermal influence. However, it is difficult to handle as contour damages such as striations and taper angle arise in the component for 3D cutting applications. Consequently, it is mainly used in industry just for simple cutting tasks. Therefore, the main goal of this study is to compensate the contour damages of 3D cutting applications by employing an optimized model for 3D waterjet cutting. By using the optimized model with a particular dynamic process control, the necessary required inputs of the currently prevailing 3D waterjet processing are decreased. Moreover, these processes have been optimized in terms of reducing the striation and taper angle formation. By overcoming the contour damages during 3D waterjet cutting, the utilization potential of the waterjet machining for modern productions has been increased.
  • Publication
    Pure waterjet controlled depth machining for stripping ceramic thermal barrier coatings on turbine blades
    ( 2019)
    Bergs, Thomas
    ;
    Borrmann, Jan Philipp
    ;
    Schüler, Manuel
    ;
    Herrig, Tim
    ;
    Döring, Jens-Erich
    Gas turbine blades are high-performance composite parts made of nickel-based superalloys coated with a bilayer coating system for thermal protection. This coating system consists of a metallic bond coat and a ceramic thermal barrier coating (TBC), typically made of yttria-stabilized zirconia. During gas turbine operation the coating system undergoes degeneration and needs to be renewed periodically. Conventional overhaul processes remove the TBC and bond coat completely in several machining steps consisting of mechanical grid blasting and chemical stripping processes. Currently selective removal of TBC without influencing the bond coat is not applicable. Pure waterjet (PWJ) controlled depth machining promises to be one of the most flexible non-conventional structuring techniques for TBC materials. Selective TBC stripping promises the flexibility of either complete or locally restricted TBC removal without damaging or contaminating the bond coat. For economic industrial use of this environmental-friendly process a complete Computer-aided (CAx) toolchain comprising Computer-aided drawing (CAD), Computer-aided manufacturing (CAM) and complementary process analysis is needed. Presently no suitable CAx toolchain supports this innovative PWJ process for defined layer machining of composite parts. This paper shows the integration of PWJ controlled depth machining process within CAx toolchain in Siemens NX for selective stripping TBC on complex free-form surfaces. The strong dependence of the machining results on energy input per unit length leads to challenges for synchronization of parametrization and machine dynamics. The evaluation of different machining strategies and machining head configurations resulted in an increasing process performance and economic efficiency of this developed PWJ process.