Univ. Prof. Dr. Ing.

Bergs, Thomas

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  • Publication
    Relating wear stages in sheet metal forming based on short- and long-term force signal variations
    ( 2022)
    Niemietz, P.
    ;
    Kornely, M.J.K.
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    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
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    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
    Methodology for the integrative adaption of manufacturing process and inspection sequences to component changes of safety-critical medical products
    ( 2022)
    Stauder, L.
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    Knott, A.L.
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    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
    A study on abrasive waterjet multi-stage machining of ceramics
    ( 2022)
    Schüler, Manuel
    ;
    Herrig, T.
    ;
    Bergs, Thomas
    Abrasive waterjet (AWJ) milling is a promising technique for machining hard materials, but it is also complex to implement. In modern production scenarios, multi-stage machining is a matter of course to improve both performance and quality. Since AWJ milling is still developing, there is little knowledge about a corresponding process design. In this study, an innovative approach for AWJ multi-stage machining of a ceramic specimen is experimentally investigated. To produce either a high removal rate or a fine surface, different parameters of abrasive grit interacting with the workpiece surface and its potential for surface integrity are analyzed for future applications.
  • Publication
    Methodology for the self-optimizing determination of additive manufacturing process eligibility and optimization potentials in toolmaking
    ( 2022)
    Dannen, Tammo
    ;
    Schindele, Benedikt
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    Prümmer, Marcel
    ;
    Arntz, Kristian
    ;
    Bergs, Thomas
    Additive Manufacturing (AM) of metallic workpieces faces a continuously rising technological relevance and market size. Producing complex or highly strained unique workpieces is a significant field of application, making AM highly relevant for tool components. Its successful economic application requires systematic workpiece based decisions and optimizations. Considering geometric and technological requirements as well as the necessary post-processing makes deciding effortful and requires in-depth knowledge. As design is usually adjusted to established manufacturing, associated technological and strategic potentials are often neglected. To embed AM in a future proof industrial environment, software-based self-learning tools are necessary. Integrated into production planning, they enable companies to unlock the potentials of AM efficiently. This paper presents an appropriate methodology for the analysis of process-specific AM-eligibility and optimization potential, added up by concrete optimization proposals. For an integrated workpiece characterization, proven methods are enlarged by tooling-specific figures. The first stage of the approach specifies the model's initialization. A learning set of tooling components is described using the developed key figure system. Based on this, a set of applicable rules for workpiece-specific result determination is generated through clustering and expert evaluation. Within the following application stage, strategic orientation is quantified and workpieces of interest are described using the developed key figures. Subsequently, the retrieved information is used for automatically generating specific recommendations relying on the generated ruleset of stage one. Finally, actual experiences regarding the recommendations are gathered within stage three. Statistic learning transfers those to the generated ruleset leading to a continuously deepening knowledge base. This process enables a steady improvement in output quality.
  • 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.
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    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
    Development of a process signature for electrical discharge machining
    ( 2022)
    Klink, A.
    ;
    Schneider, S.
    ;
    Bergs, Thomas
    Electrical discharge machining (EDM) is a versatile unconventional machining process allowing high precision manufacturing. Due to the thermal main active principle, the process-induced heat affected rim zone always needs to be particularly considered regarding its characteristics as the resulting surface integrity has to fulfill the needed functional properties for advanced applications. Today, no deterministic model is available especially for the residual stress prediction. As consequence, current process design is based on experience and heuristic optimization. The paper therefore mechanistically links the material modification and the process-induced load. Inversion of the according process signature component finally allows model-based process design.
  • 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
    ;
    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.