Univ. Prof. Dr. Ing.

Bergs, Thomas

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  • Publication
    Electrochemical Defect Analysis of Additive Manufactured Components
    ( 2022)
    Sous, Florian
    ;
    Herrig, Tim
    ;
    Bergs, Thomas
    ;
    Karges, Florian
    ;
    Feiling, Nicole
    ;
    Zeis, Markus
    Due to more freedom in design and flexibility in production, parts produced by additive manufacturing (AM) technologies offer a huge potential for the manufacture of turbomachinery components. Because of the layer by layer built structure, internal defects such as cracks or gaseous pores can occur. These defects considerably reduce the mechanical properties and increase the importance of quality control, especially in the field of turbomachinery. Therefore, in this study, an electrochemical defect analysis (EC-D) of additive manufactured components is introduced, performed, and validated in comparison to a nondestructive X-ray testing of the same part. A test rig was developed, which allows an alternation between electrochemical machining and subsequent optical documentation of each removed layer. The documentation of the surface and the macroscopic defects in the AM-parts are captured by an integrated camera system.
  • Publication
    Visualization of Spatially Resolved Energy in Wire Electrical Discharge Machining
    ( 2021)
    Küpper, Ugur
    ;
    Herrig, Tim
    ;
    Bergs, Thomas
    For the development of a process monitoring system in wire EDM, a model for mapping the material removal based on process data is necessary. In order to use the causal relationship between the process energy and the material removal, the individual discharges must first be digitally mapped on the machined surface. In the context of this work, the discharge position is detected considering the individual discharge energy in order to allow the mapping of the spatially resolved process energy. For this purpose, test series are carried out to correlate the discharge position with the difference between the upper and lower current using a real-time capable measuring system.
  • 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
    Systematic Change of Abrasive Size Distribution
    ( 2021)
    Bergs, Thomas
    ;
    Schüler, Manuel
    ;
    Herrig, Tim
    ;
    Fernolendt, Jan
    ;
    Linde, Marco
    The continuous suspension (ConSus) technology is a new coming approach that promises performance advantages over industrially used abrasive waterjet (AWJ) systems in production scenarios. However, it currently lacks practical experience and process parametrization is typically still empirical of either using a 2-phase abrasive suspension jet (ASJ) or a 3-phase injection AWJ tool. A practical comparison of respective AWJ tool characteristics of prior work piece contact is needed for fundamental parametrization. An experimental approach was used to compare the respective AWJ systems. The abrasive material was compared before and after going through either an injection AWJ head or a ConSus ASJ system. Typical abrasive materials and mesh sizes for AWJ machining were systematically investigated. This paper shows that current AWJ cutting systems yield different results when using equal abrasive material. ConSus shows almost no significant effect on abrasive size distribution while commonly used injector systems shifts a tremendous portion of the original abrasive to smaller grain sizes. Therefore, the results enhance process understanding and revision of existing process models for future applications.
  • Publication
    Electrochemical defect analysis (EC-D) of additive manufactured components
    ( 2021)
    Sous, Florian
    ;
    Herrig, Tim
    ;
    Bergs, Thomas
    ;
    Karges, Florian
    ;
    Feiling, Nicole
    ;
    Zeis, Markus
    Due to more freedom in design and flexibility in production, parts produced by additive manufacturing technologies (AM) offer a huge potential for the manufacture of turbomachinery components. Because of the layer by layer built structure, internal defects like cracks or gaseous pores can occur. These defects considerably reduce the mechanical properties and increase the importance of quality control, especially in the field of turbomachinery. Therefore, in this study, an electrochemical defect analysis (EC-D) of additive manufactured components is introduced, performed and validated in comparison to a nondestructive X-ray testing of the same part. A test rig was developed, which allows an alternation between electrochemical machining and subsequent optical documentation of each removed layer. The documentation of the surface and the macroscopic defects in the AM-parts are captured by an integrated camera system.
  • Publication
    Influence of Abrasive Properties on Erosion in Waterjet Machining
    ( 2021)
    Schüler, Manuel
    ;
    Dadgar, Mohammad
    ;
    Herrig, Tim
    ;
    Bergs, Thomas
    In the recent decades abrasive waterjet (AWJ) machining has been successfully established as a highly flexible, non-conventional production technique with significant productivity advantages for hard-to-machine materials. However, the remaining challenging issue with this technology is how to control the influencing factors affecting the erosion process. For AWJ machining, the abrasive grit interaction is considered to be the most important factor during the erosion process. To attain a more profound understanding of the AWJ erosion process, the physical phenomena of grit interaction on the machining result need to be investigated. Therefore, diverse abrasive grit of individual shape and mechanical properties were used in the course of the experiments with subsequent visual analyses of the machining results supplemented by residual stress measurements. This study has identified essential process mechanisms required for the modeling of AWJ machining operations.
  • 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
    Fracture toughness and tribological properties of cemented carbides machined by sinking electrical discharge machining
    ( 2021)
    Petersen, Timm
    ;
    Küpper, Ugur
    ;
    Herrig, Tim
    ;
    Klink, Andreas
    ;
    Bergs, Thomas
    The quality of a forming process highly depends on the pressure applied to the workpiece. Consequently, the demand for higher workpiece qualities results in a demand for tools that can withstand high compressive stresses. Moreover, the tendency of using materials like high-strength steels as workpiece material, urges the need for tool materials that can withstand high compressive stresses and are resistant to wear. A class of materials that offer a combination of hardness or wear resistance and ductility are cemented carbides. However, these properties hamper their machining with conventional cutting technologies. Due to its electro-thermal working principle, Electrical Discharge Machining (EDM) is able to machine materials independently from their mechanical properties. On the other hand, the removal process is accompanied by thermal stresses, which can cause residual stresses and micro cracks near the machined surface. Due to their pre-existing stresses from the sinte ring process, cemented carbides are especially susceptible for these kind of damages. It is therefore necessary to identify the impact of EDM on the material. Different machining strategies are tested with two different types of cemented carbides and examined regarding their fracture toughness. The crack surfaces resulting from the three point bending test are microscopically inspected regarding failure initiation. Additionally pin-on-disc tests are conducted to determine the influence of the EDM strategies on the tribological properties of the machined cemented carbides.
  • Publication
    Wire electrical discharge machinability and load-bearing capacity of ATZ-WC composite ceramics
    ( 2021)
    Olivier, Marcel
    ;
    Heß, Raphael
    ;
    Gommeringer, Andrea
    ;
    Kern, Frank
    ;
    Herrig, Tim
    ;
    Bergs, Thomas
    Electrically conductive and thereby electrical discharge machinable ceramics may gain further relevance for tooling applications and in chemical industry. They combine high chemical and thermal durability with high hardness and strength. While these properties represent a significant advantage for application, they are a major challenge for conventional machining. Due to the thermophysical removal principle, wire electrical discharge machining (WEDM) is a suitable manufacturing process for hardness-independent machining and may broaden the use of ceramics especially in case of customized complex parts. Up to now, there are only a few investigations on WEDM of electrically conductive ceramics, especially with regard to the surface integrity and the influence of the EDM process on the mechanical properties. A previous study investigated the influence of different WEDM technologies on the surface integrity and the resulting load-bearing capacity of a zirconia-tungsten carb ide (TZP-WC) ceramic. Based on this investigation, the heat flow in this ceramic composite was calculated with the use of a heat simulation model and compared with the analyzed rim zone, in order to predict a priori reliable process parameters. Furthermore, the wire electrical machinability and the bending strength of alumina-zirconia-tungsten carbide (ATZ-WC) composite ceramics with different fractions of the respective phases were investigated to identify the correlations and verify the simulation model.