Univ. Prof. Dr. Ing.

Bergs, Thomas

Filters
19
Reset filters

Settings
Now showing 1 - 10 of 19
  • 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
    Analysis of the thermo-mechanical load and productivity during force-compliant grinding of pcBN
    ( 2022)
    Müller, U.
    ;
    Prinz, S.
    ;
    Barth, S.
    ;
    Bergs, Thomas
    Superhard cutting tool materials such as polycrystalline cubic boron nitride (pcBN) are increasingly demanded in the aerospace and automotive industries. Although grinding is a common manufacturing technology for pcBN cutting tools, the lack of knowledge regarding thermal and mechanical loads during grinding of pcBN can cause workpiece damage and high grinding wheel wear. Therefore, this work presents a new approach of force-compliant grinding (FCG) of different pcBN specifications considering the thermal and mechanical load as well as the productivity. During the FCG approach, the normal force between the grinding wheel and the pcBN workpiece was set to a predefined value before material removal starts. Based on an evaluation of the grinding force ratio, the temperature of contact and the material removal rate, a modification of Preston's theory of polishing was found to be applicable to predict the productivity. Accordingly, both an increasing grinding normal force and grinding force ratio lead to an increasing productivity during FCG of pcBN. However, the quantitative models developed in this work enable to predict the productivity as well as the mechanical and thermal load during FCG of pcBN. These models hence contribute to the extension of process knowledge for grinding pcBN and thus to prevent damage to the workpiece and high wear of the grinding wheel.
  • 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.
  • 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
    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
    Methodology for the integrative adaption of manufacturing process and inspection sequences to component changes of safety-critical medical products
    ( 2022)
    Stauder, L.
    ;
    Knott, A.L.
    ;
    Schmitt, Robert
    ;
    Bergs, Thomas
    Ever-shorter product lifecycles and more frequently changing customer demands challenge manufacturing companies to change their products and the components these products are composed of in ever-shorter periods. As a result, the existing manufacturing process and inspection sequences (MPISs) of the corresponding components must be adapted. Particularly in the production of safety–critical components, such as in the medical industries, component changes represent a major challenge, as very high quality requirements are placed on the components and a costly re-certification of the adapted processes is necessary. Due to the high quality requirements, not only the manufacturing process but also the inspection processes must be adapted for the realization of a component change. Furthermore, a high degree of planning reliability is necessary when deriving adaptations of MPISs for component changes to keep the re-certification effort and adaptation costs for safety–critical components as low as possible. Therefore, a methodology is introduced for the integrative derivation of adaptation options of MPISs due to component changes that supports users in identifying suitable adaptations in a systematic and time-efficient way. The methodology is successfully applied to a use case from the medical industry and supports users in identifying adaptations in established MPISs to implement a component change.
  • Publication
    Relating wear stages in sheet metal forming based on short- and long-term force signal variations
    ( 2022)
    Niemietz, P.
    ;
    Kornely, M.J.K.
    ;
    Trauth, D.
    ;
    Bergs, Thomas
    Monitoring systems in sheet metal forming cannot rely on direct measurements of the physical condition of interest because the space between the die component and the material is inaccessible. Therefore, in order to gain further insight into the forming or stamping process, sensors must be used to detect auxiliary quantities such as acoustic emission and force that relate to the physical quantities of interest. While it is known that changes in force data are related to physical parameters of the process material, lubricant used, and geometry, the changes in data over large stroke series and their relationship to wear are the subject of this paper. Previously, force data from different wear conditions (artificially introduced into the system and not occurring in an industry-like environment) were used as input for clustering and classifying high and low wear force data. This paper contributes to fill the current research gap by isolating structural properties of data as indicators of wear growth to quantify the wear evolution during ongoing production in industry-like scenarios. The selected methods represent either established methods in sheet metal forming force data analysis, dimensionality reduction for local structure separation or generic feature extraction. The study is conducted on a set of four experiments with each containing about 3000 strokes.
  • 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
    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
    Modeling of the temperature field induced during electrical discharge machining
    ( 2022)
    Schneider, S.
    ;
    Herrig, T.
    ;
    Klink, A.
    ;
    Bergs, Thomas
    Electrical discharge machining is a process with main thermal active principal. Thus, for example for steel materials it is unavoidable to modify the rim zone of the final workpiece. Knowledge or even prediction of these modifications would improve industrial applications. Basis for this is the information about the time and locally resolved temperature field, which is not available in that form today. Hence the objective of this work is to establish a model of the temperature field within the electrodes rim zone during electrical discharge machining process. In this work, this field is modeled for the electrical discharge machining process based on the measurable discharge energy of a single discharge. First, an energy dissipation model for a single discharge is presented. In the next step, the interaction of two consecutive discharges is analyzed. Both results are the inputs for a macroscopic process model to calculate the temperature field of the whole workpiece. Finally, by coupling this macroscopic temperature field and the single discharge model it is possible to determine the locally resolved temperature field at any time of the process. For typical conditions, it is very unlikely that two discharges affect each other regarding overlaying temperature fields in the micro range but over time, a macroscopic heating could take place depending on the dielectric cooling efficiency.