Univ. Prof. Dr. Ing.

Bergs, Thomas

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  • Publication
    Experimental investigation on friction under machining conditions with cutting fluid supply
    ( 2022)
    Gerhard, Nicklas
    ;
    Göttlich, Tim
    ;
    Schraknepper, Daniel
    ;
    Bergs, Thomas
    In cutting processes, friction is mainly present on the rake and flank face of the tool. It has a direct influence on the thermo-mechanical loads applied in the cutting zone and thus on the surface integrity. To investigate the friction behavior experimentally, a friction test bench based on a lathe with cutting fluid supply was developed. Workpiece temperature was studied depending on machining conditions. The friction tests showed that the cutting fluid led to higher friction forces under the conditions investigated. Furthermore, the results revealed that an increase in the frictional force was accompanied by an increase in workpiece temperature.
  • Publication
    Influence of relative velocity and contact force between abrasive media and workpiece on material removal in gyro finishing
    ( 2022)
    Ohlert, M.
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    Brüssel, F.
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    Prinz, S.
    ;
    Barth, S.
    ;
    Bergs, Thomas
    Gyro finishing is capable of reducing the surface roughness and inducing residual compressive stresses into the edge zone of the component to enhance the fatigue strength. Due to an insufficient understanding of gyro finishing processes, it is not possible to adjust the process result in a knowledge-based manner. In order to understand the mechanisms of action in the process, knowledge of the contact between abrasive media and workpiece is necessary. This paper presents the analysis of the contact conditions and the process state variables between abrasive media and workpiece with two measuring systems. Furthermore, the influence of the contact conditions and the process state variables on the material removal mass was investigated. Therefore, analogy workpieces were machined by gyro finishing using different process state variables and abrasive media specifications. Based on the results, an empirical-analytical model is derived, which is able to describe the material removal mass depending on the contact conditions and the process state variables between abrasive media and workpiece.
  • 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
    Evaluation of the influence of different milling parameters and tool wear on the rim zone of a 5-axis milled large gear
    ( 2022)
    Zachert, Christoph
    ;
    Greschert, René
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    Schraknepper, Daniel
    ;
    Brimmers, Jens
    ;
    Bergs, Thomas
    Machining of gears by 5-axis milling allows additional degrees of freedom in gear design compared to conventional hobbing processes. Changes in the machining technology influence the surface integrity and, thus, the service life of the machined gears. For this reason, different machining parameters were investigated regarding their effects on the surface layer and subsequently on service life. In this paper, the residual stresses and microstructures of a large gear manufactured by 5-axis milling and the service life of test gears are analyzed. With the results from this paper, the surface integrity and service life can be predicted depending on the machining parameters.
  • Publication
    Investigation of residual stresses and workpiece distortion during high-feed milling of slender stainless steel components
    ( 2022)
    Liu, Hui
    ;
    Schraknepper, Daniel
    ;
    Bergs, Thomas
    In high-feed milling, the workpiece surface is subjected to high thermo-mechanical loads, which leads to excessive changes in residual stresses and thus affects the quality of the product. In this work, the influence of tool geometry and cutting speed on the residual stress state and the resulting workpiece distortion was investigated. Machining tests were performed by face milling of slender parts made of low sulfur stainless steel X2CrNiMo17-12-2. The results showed that the macro-geometry of the tool has a major influence on the surface topography and residual stresses. The cutting edge radii have barely any influence on the residual stresses under the conditions investigated.
  • 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
    Analysis of tool wear in face hobbing plunging manufacturing processes
    ( 2022)
    Alexopoulos, Charalampos
    ;
    Brimmers, Jens
    ;
    Bergs, Thomas
    For soft machining of bevel gears, multi-part tool systems consisting of a cutter head and stick blades are commonly used. In the past, experimental investigations regarding the tool wear in bevel gear milling have been carried out, aiming to optimize the process design and thus the process economic efficiency. However, the existing investigations refer only to face milling processes. In this paper, a tool wear study for an industrial application of the face hobbing plunging process is presented. Additionally an analogy trial of the process is designed. Based on the findings, it is concluded that the designed analogy trial is suitable for analyzing the tool wear development for face hobbing plunging processes.
  • 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.
  • Publication
    Investigation of the cutting fluid’s flow and its thermomechanical effect on the cutting zone based on fluid-structure interaction (FSI) simulation
    ( 2022)
    Liu, H.
    ;
    Meurer, M.
    ;
    Schraknepper, D.
    ;
    Bergs, Thomas
    Cutting fluids are an important part of today’s metal cutting processes, especially when machining aerospace alloys. They offer the possibility to extend tool life and improve cutting performance. However, the equipment and handling of cutting fluids also raises manufacturing costs. To reduce the negative impact of the high cost of cutting fluids, cooling systems and strategies are constantly being optimized. In most existing works, the influences of different cooling strategies on the relevant process state variables, such as tool wear, cutting forces, chip breakage, etc., are empirically investigated. Due to the limitations of experimental methods, analysis and modeling of the working mechanism has so far only been carried out at a relatively abstract level. For a better understanding of the mechanism of cutting fluids, a thermal coupled two-dimensional simulation approach for the orthogonal cutting process was developed in this work. This approach is based on the Coupled Eulerian Lagrangian (CEL) method and provides a detailed investigation of the cutting fluid’s impact on chip formation and tool temperature. For model validation, cutting tests were conducted on a broaching machine. The simulation resolved the fluid behavior in the cutting area and showed the distribution of convective cooling on the tool surface. This work demonstrates the potential of CEL-based cutting fluid simulation, but also pointed out the shortcomings of this method.