Univ. Prof. Dr. Ing.

Bergs, Thomas

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  • Publication
    Knowledge-Based Adaptation of Product and Process Design in Blisk Manufacturing
    ( 2022)
    Ganser, Philipp
    ;
    Landwehr, Markus
    ;
    Schiller, Sven
    ;
    Vahl, Christopher
    ;
    Mayer, Sebastian
    ;
    Bergs, Thomas
    Early and efficient harmonization between product design and manufacturing represents one of the most challenging tasks in engineering. Concepts such as simultaneous engineering aim for a product creation process, which addresses both, functional requirements as well as requirements from production. However, existing concepts mostly focus on organizational tasks and heavily rely on the human factor for the exchange of complex information across different domains, organizations, or systems. Nowadays product and process design make use of advanced software tools such as computer-aided design, manufacturing, and engineering systems (CAD/CAM/CAE). Modern systems already provide seamless integration of both worlds in a single digital environment to ensure a continuous workflow. Yet, for the holistic harmonization between product and process design, the following aspects are missing: (i) the digital environment does not provide a complete and data consistent digital twin of the component; this applies especially to the process design and analysis environment, (ii) due to the lack of process and part condition data in the manufacturing environment, an adaptation of product and process design for a balanced functionality and manufacturability is hindered, and (iii) systematic long-term data analytics across different product and process designs with the ultimate goal to transfer knowledge from one product to the next and to accelerate the entire product development process is not considered. This paper presents an exploration concept which couples product design (CAD), process design (CAM), process simulation (CAE), and process adaptation in a single software system. The approach provides insights into correlations and dependencies between input parameters of product/process design and the process output. The insights potentially allow for a knowledge-based adaptation, tackling well-known optimization issues such as parameter choice or operation sequencing. First results are demonstrated using the example of a blade integrated disk (blisk). Early and efficient harmonization between product design and manufacturing represents one of the most challenging tasks in engineering. Concepts such as simultaneous engineering aim for a product creation process, which addresses both, functional requirements as well as requirements from production. However, existing concepts mostly focus on organizational tasks and heavily rely on the human factor for the exchange of complex information across different domains, organizations, or systems. Nowadays product and process design make use of advanced software tools such as computer-aided design, manufacturing, and engineering systems (CAD/CAM/CAE). Modern systems already provide seamless integration of both worlds in a single digital environment to ensure a continuous workflow. Yet, for the holistic harmonization between product and process design, the following aspects are missing: (i) the digital environment does not provide a complete and data consistent digital twin of the component; this applies especially to the process design and analysis environment, (ii) due to the lack of process and part condition data in the manufacturing environment, an adaptation of product and process design for a balanced functionality and manufacturability is hindered, and (iii) systematic long-term data analytics across different product and process designs with the ultimate goal to transfer knowledge from one product to the next and to accelerate the entire product development process is not considered. This paper presents an exploration concept which couples product design (CAD), process design (CAM), process simulation (CAE), and process adaptation in a single software system. The approach provides insights into correlations and dependencies between input parameters of product/process design and the process output. The insights potentially allow for a knowledge-based adaptation, tackling well-known optimization issues such as parameter choice or operation sequencing. First results are demonstrated using the example of a blade integrated disk (blisk).
  • Publication
    Process stabilization through pulsed laser-induced melt pool shaping in dual-beam LMD
    ( 2022)
    Gipperich, Marius
    ;
    Gräfe, Stefan
    ;
    Day, Robin
    ;
    Bergs, Thomas
    Laser Metal Deposition (LMD) is an additive manufacturing process that reaches high deposition rates. Its applications are mainly found in repair, cladding and manufacturing. The two commonly used LMD processes are powder-based (LMD-p) and wire-based (LMD-w). Despite the fact that wire-based LMD uses material more efficiently, its process stability is a major concern. One approach to increase the process stability is superposing a pulsed laser (pw) beam with the conventionally used continuous laser (cw). Previous studies have shown that the metal vapor caused by pulsed laser-induced evaporation in the process zone significantly improves energy absorption. Furthermore, a direct relation between vapor pressure and melt pool form has been demonstrated. In this contribution, we correlate the pw-controlled melt pool geometry to process stability. High-speed camera imaging is employed to evaluate the dynamic melt pool behavior as a function of pw frequency and power. It is shown that irregular melt pool oscillations impairing process stability in conventional LMD-w are reduced if the pulsed laser is added. The melt front is shaped depending on the acting pw-induced pressure. This leads to a more stable interaction between wire and melt pool. Furthermore, the pw pressure changes the welding bead height and width. This cross-sectional geometry has an impact on the resulting waviness in 3D build-up. We also investigate how the waviness influences process stability during multilayer LMD-w. The results demonstrate that the dual beam technology is a promising way to develop more reliable and resource-efficient AM processes.
  • Publication
    Express Wire Coil Cladding as an Advanced Technology to Accelerate Additive Manufacturing and Coating
    ( 2022)
    Gipperich, Marius
    ;
    Riepe, Jan
    ;
    Day, Robin
    ;
    Bergs, Thomas
    Metal shafts are indispensable components in mobility, energy and mechanical engineering. In such applications, the shafts need to withstand severe mechanical loads, friction, high temperature or corrosive media. This is why shafts are often completely made of high-performance alloys. From a technical point of view, coating an inexpensive base shaft with a thin layer of high-performance material is mostly sufficient to ensure its functionality. Adding functional parts such as bearing seats by Additive Manufacturing (AM) is an advantageous approach to increase flexibility and material efficiency. Reliable and economic AM processes need to be developed further, and laser-based processes such as wire-based Laser Metal Deposition (LMD-w) offer high potential to accomplish this. Due to their low deposition rate, however, LMD processes are not economically competitive with high-speed subtractive technologies. Motivated by this challenge, we present an alternative approach for laser-based shaft cladding. Instead of adding the filler wire continuously, wire coils are wound and preplaced on the shaft. In a second step, laser processing while rotating the part generates a metallurgical bond between the wire and the substrate. In this study, several solid and flux-cored wires were analyzed regarding their suitability for this two-step coil winding and LMD process. The resulting surface state and the welded joint quality are evaulated. Metallographic cross sections show low porosity and small heat-affected zones. Thanks to its good scalability, this innovative process can help strongly increase the build-up rate compared to classic LMD-w.
  • Publication
    Determination of the Level of Automation for Additive Manufacturing Process Chains
    ( 2021)
    Horstkotte, Rainer
    ;
    Bruning, Benedikt
    ;
    Prümmer, Marcel
    ;
    Arntz, Kristian
    ;
    Bergs, Thomas
    Industrial manufacturing is confronted with increased cost pressure due to international competition. The use of automation solutions can help to optimally exploit existing potentials and react to market competitors. In particular, increased productivity and shorter cycle times lead to reduced costs and increased capabilities. New manufacturing technologies can also help to achieve an advantage over market competitors. In recent years, additive manufacturing technologies in particular have gained in importance. Laser Powder Bed Fusion (L-PBF) is an additive manufacturing (AM) technology that enables the production of highly complex and individualized metal components. A significant disadvantage of L-PBF is the required post-processing of additive manufactured parts, which is necessary to remove auxiliary structures, separate the workpieces from the substrate plate and obtain high precision as well as low surface roughness. Automation of these post-processes is a crucial factor for increasing productivity and thus for further industrialization of L-PBF. In order to exploit this potential optimally, the level of automation has to be determined. In this paper, a methodology is presented that enables the determination of the level of automation for the additive process chain with L-BPF. The focus is on evaluating the level of automation of individual manufacturing technologies due to consideration of technology-specific requirements and characteristics. The scope of the analysis is not limited to technologies; handling processes are also taken into account. A differentiated e valuation of the level of automation is enabled by the definition of technology-specific and cross-technology sub-tasks.
  • Publication
    Express Wire Coil Cladding (EW2C) as an Advanced Technology to Accelerate Additive Manufacturing and Coating
    ( 2021)
    Gipperich, Marius
    ;
    Riepe, Jan
    ;
    Day, Robin
    ;
    Bergs, Thomas
    Metal shafts are indispensable components in mobility, energy and mechanical engineering. In such applications, the shafts need to withstand severe mechanical loads, friction, high temperature or corrosive media. This is why shafts are often completely made of high-performance alloys. From a technical point of view, coating an inexpensive base shaft with a thin layer of high-performance material is mostly sufficient to ensure its functionality. Adding functional parts such as shoulders or bearing seats by Additive Manufacturing (AM) instead of creating them by subtractive manufacturing is an advantageous approach to increase flexibility and material efficiency. Reliable and economic AM and coating processes need to be developed further, and laser-based processes such as wire-based Laser Metal Deposition (LMD-w) offer high potential to accomplish this. They can generate a stable metallurgical bond between the base material and the cladding or the added feature without excessively heating the work piece. Due to their low build-up rate, however, LMD processes are not economically competitive with high-speed subtractive technologies such as drilling or turning, which are predominately used for shaft production. Motivated by this challenge, we present an alternative approach that increases the deposition rate for laser-based shaft cladding. Instead of adding the filler wire continuously, wire coils are wound and preplaced on the shaft. In a second step, laser processing while rotating the part generates a metallurgical bond between the wire and the substrate. In this study, several solid and flux-cored wires were analyzed regarding their suitability for this two-step coil winding and LMD process. The results from LMD experiments give an overview of the resulting surface state and of the welded joint quality after deposition. Metallographic cross sections show low porosity of the deposited layers and small heat-affected zones in the base shaft. Thanks to its good scalability, this innovative two-step process can help strongly increase the build-up rate compared to classic LMD-w.
  • Publication
    Influence of heat treatment on the residual stress-related machining distortion of Ti-6Al-4V alloy monolithic parts
    ( 2021)
    Landwehr, Markus
    ;
    Oehler, Farina
    ;
    Behnken, Herfried
    ;
    Holling, Hendrik
    ;
    Sambathkumar, Raveeshankar
    ;
    Ganser, Philipp
    ;
    Bergs, Thomas
    Machining distortion caused by residual stresses is one of the major challenges in the production of thin-walled monolithic parts. One reason for the distortion is the relaxation of the initial residual stresses within the raw part due to the material removal during the machining process. The initial residual stresses mainly depend on the manufacturing process of the raw part and the subsequent heat treatment. This paper presents the results from a set of experimental and computational studies of the influence of heat treatment on residual stress-related machining distortion of Ti-6Al-4V alloy monolithic parts. A thermo-mechanical simulation of the heat treatment process is developed for the prediction of the initial residual stresses. For experimental validation, the contour method is use d to quantify the initial residual stresses. Finally, machining tests are conducted to measure the final part distortion for two different residual stress states.
  • Publication
    A Cradle to Gate Approach for Life-Cycle-Assessment of Blisk Manufacturing
    ( 2021)
    Fricke, Kilian
    ;
    Gierlings, Sascha
    ;
    Ganser, Philipp
    ;
    Seimann, Martin
    ;
    Bergs, Thomas
    The aviation industry has been growing continuously over the past decades. Despite the current Covid-19 crisis, this trend is likely to resume in the near future. On an international level, initiatives like the Green Recovery Plan promoted by the European Union set the basis towards a more environmentally friendly future approach for the aero-industry. The increasing air traffic and the focus on a more sustainable industry as a whole lead to an extensive need for a more balanced assessment of a products life cycle especially on an ecological level. Blisks (or IBRs) remain a central component of every current and very possible every future aero engine configuration. Their advantages during operation compared to conventional compressor rotors are met with a considerably complex manufacturing and production process. In the high-pressure compressor segment of an engine, the material selection is limited to Titanium alloys such as Ti6Al4V and heat-resistant Nickel-alloys such as Inconel718. The corresponding process chains consist of numerous different process steps starting with the initial raw material extraction and ending with the quality assurance (cradle to gate). Especially the central milling process requires a highly qualified process design to ensure a part of sufficient quality. Life-Cycle-Assessments enable an investigation of a products overall environmental impact and ecological footprint throughout its distinct life-cycle. Formal LCAs are generally divided by international standards into four separate steps of analysis: the goal and scope definition, the acquisition of Life Cycle-Inventory, the Life-Cycle-Impact-Assessment and the interpretation. This content of this paper focuses on a general approach for Life-Cycle-Assessment for Blisk manufacturing. Firstly, the goal and scope is set by presenting three separate process chain scenarios for Blisk manufacturing, which mainly differ in terms of raw material selection and individual process selections for blade manufacturing. Secondly, the LCI data (Life-Cycle Inventory) acquisition is illustrated by defining all significant in- and outputs of each individual process step. Thirdly, the approach of a Life-Cycle-Impact-Assessment is presented by introducing the modelling approach in an LCA-software environment. Fourthly, an outlook and discussion on relevant impact-indicators for a subsequent interpretation of future results are conducted.
  • 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.