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
    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
    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
    Review on model predictive control: an engineering perspective
    ( 2021)
    Schwenzer, Max
    ;
    Ay, Muzaffer
    ;
    Bergs, Thomas
    ;
    Abel, Dirk
    Model-based predictive control (MPC) describes a set of advanced control methods, which make use of a process model to predict the future behavior of the controlled system. By solving a-potentially constrained-optimization problem, MPC determines the control law implicitly. This shifts the effort for the design of a controller towards modeling of the to-be-controlled process. Since such models are available in many fields of engineering, the initial hurdle for applying control is deceased with MPC. Its implicit formulation maintains the physical understanding of the system parameters facilitating the tuning of the controller. Model-based predictive control (MPC) can even control systems, which cannot be controlled by conventional feedback controllers. With most of the theory laid out, it is time for a concise summary of it and an application-driven survey. This review article should serve as such. While in the beginnings of MPC, several widely noticed review paper have been published, a comprehensive overview on the latest developments, and on applications, is missing today. This article reviews the current state of the art including theory, historic evolution, and practical considerations to create intuitive understanding. We lay special attention on applications in order to demonstrate what is already possible today. Furthermore, we provide detailed discussion on implantation details in general and strategies to cope with the computational burden-still a major factor in the design of MPC. Besides key methods in the development of MPC, this review points to the future trends emphasizing why they are the next logical steps in MPC.
  • Publication
    Design of economically-optimized manufacturing process sequences using cross-process models
    ( 2021)
    Beckers, Alexander
    ;
    Stauder, Lars
    ;
    Grünebaum, Timm
    ;
    Barth, Sebastian
    ;
    Bergs, Thomas
    Manufacturing companies have to design their manufacturing process sequences so that the product requirements are fulfilled cost-efficiently. It is important that process sequences are designed holistically and that the technological and economic relationships between individual processes are taken into account. It is particularly important to consider these relationships in serial production, because technology experts often design manufacturing processes one process at a time. While the different processes are linked at higher planning levels, the relationships between the manufacturing processes are insufficiently considered. At the design phase, the economic potential of cross-process optimization could be tapped into but remains unused. An approach for the design of economically-optimized manufacturing process sequences is presented in this paper. It describes how technological relationships in a process sequence can be modeled using cross-process models. The approach includes a newly developed model which can be used to economically evaluate process sequences. Within this model, process parameter-dependent variables of the individual manufacturing processes and temporal as well as technological relationships between the processes are considered in order to optimize manufacturing process sequences. A case study shows the potential of cross-process optimization.
  • Publication
    Development of a virtual sensor for the comparison of heat partitions in milling under cryogenic cooling lubrication and high-pressure cutting fluid supply
    ( 2021)
    Augspurger, Thorsten
    ;
    Koch, Matthias
    ;
    Lakner, Thomas
    ;
    Bartolomeis, Andrea de
    ;
    Shokrani, Alborz
    ;
    Bergs, Thomas
    Manufacturing high precision and high performance parts in aerospace, automotive and medical industries often requires machining of difficult-to-cut materials such as titanium, nickel and hardened alloyed steel alloys. Low productivity and environmental damage are major problems in cutting these materials, which vitally require optimized cooling strategies. High-pressure cutting fluid supply (HP CF) and cryogenic cooling lubrication (CRYO CL) are two of the most effective cooling lubrication approaches to increase tool life, productivity and avoid scrap production. The scientific and knowledge-based application of HP CF and CRYO CL had a pivotal role in improving the machining of difficult-to-cut materials, specifically in milling processes. In this context, the quantification of the cooling and lubrication effect of HP CF and CRYO CL is essential in order to adapt to the fluctuating heat generation at the cutting zone. The novel concept of a soft sensor for the quantification of the cooling and lubrication effect in the milling process is presented in this paper. This soft sensor integrates force measurements and transient temperature data from the process with the help of a mechanical model as well as an inverse temperature model. These models elevate the measured force and temperature signals to heat flows and power in the thermodynamic domain enabling an energy balancing in the real milling application. A telemetry system was used to measure the transient temperature in the milling tool with embedded thermocouples when milling 42CrMo4 and Ti-6Al-4 V in av and v conditions. This way the separated cooling versus lubrication effect of high-pressure cutting fluid supply and a single channel cryogenic cooling lubrication based on carbon dioxide (CO2) and oil is investigated and compared with dry machining at various cutting parameters and proceeding tool wear.
  • Publication
    Digital image correlation analysis and modelling of the strain rate in metal cutting
    ( 2021)
    Bergs, Thomas
    ;
    Abouridouane, Mustapha
    ;
    Meurer, Markus
    ;
    Peng, Bingxiao
    In the last eight decades, considerable modelling and computational efforts have been made to predict the strain rate during cutting with the aim of optimizing machining processes. However, the validation of these modelling approaches on a local scale remains excessively limited due to the lack of in-situ measurements and the faulty existing quick-stop tests. This work presents the in-process analysis of the strain rate and strain in the primary shear zone using high speed Digital Image Correlation (DIC) techniques. The comparison of measured and computed results shows the suitability of the DIC techniques and the robustness of the modelling approaches.
  • Publication
    Influence of the frequency of pulsating high-pressure cutting fluid jets on the resulting chip length and surface finish
    ( 2021)
    Splettstoesser, Antonia
    ;
    Schraknepper, Daniel
    ;
    Bergs, Thomas
    High-pressure cutting fluid supply is a proven technology for chip breaking when turning difficult-to-cut materials, such as Inconel 718. However, the technology is usually not suitable for the finish turning of safety-critical parts in aero engines. The acting force of the cutting fluid jet on the back of the chip causes chip breaking. The broken chips are then accelerated by the cutting fluid jet towards the workpiece surfaces where they cause damage on impact. One approach to minimize surface damage is a specific increase in the chip length. The center of gravity of the chips with an adjusted length is shifted out of the focus where the cutting fluid jet hits the chips. Hence, the already finished surface is subjected to fewer impacts of the chips. In this study, the adjustment of the chip length by pulsating high-pressure cutting fluid supply to prevent surface damage was investigated. A valve unit was used to generate two alternating cutting fluid supply pressure levels in certain time intervals. During the low-pressure stage, the force of the cutting fluid jet does not lead to chip breakage and the chip length increases until the valves switch and the high-pressure stage is released. The focus of this work was the analysis of the relationship between the duration of the low-pressure and high-pressure time intervals and the chip length. Additionally, the influence of the depth of cut, the feed, and the cutting speed on the chip length during pulsating high-pressure cutting fluid supply was investigated. Finally, a case study was carried out to evaluate the effectiveness of the pulsating high-pressure cutting fluid supply technology. Therefore, the shoulder surface of a demonstrator part was finished by face turning. Following, the cylindrical surface was finished with a continuous and pulsating high-pressure cutting fluid supply with varied supply parameters. Microscopic analyses of the surface prove that the pulsating high-pressure cutting fluid supply prevents the surface from being damaged by the impacts of chips.
  • Publication
    Considering multiple process observables to determine material model parameters for FE-cutting simulations
    ( 2021)
    Hardt, Marvin
    ;
    Bergs, Thomas
    Analyzing the chip formation process by means of the finite element method (FEM) is an established procedure to understand the cutting process. For a realistic simulation, different input models are required, among which the material model is crucial. To determine the underlying material model parameters, inverse methods have found an increasing acceptance within the last decade. The calculated model parameters exhibit good validity within the domain of investigation, but suffer from their non-uniqueness. To overcome the drawback of the non-uniqueness, the literature suggests either to enlarge the domain of experimental investigations or to use more process observables as validation parameters. This paper presents a novel approach merging both suggestions: a fully automatized procedure in conjunction with the use of multiple process observables is utilized to investigate the non-uniqueness of material model parameters for the domain of cutting simulations. The underlying approach is two-fold: Firstly, the accuracy of the evaluated process observables from FE simulations is enhanced by establishing an automatized routine. Secondly, the number of process observables that are considered in the inverse approach is increased. For this purpose, the cutting force, cutting normal force, chip temperature, chip thickness, and chip radius are taken into account. It was shown that multiple parameter sets of the material model can result in almost identical simulation results in terms of the simulated process observables and the local material loads.
  • Publication
    Tool wear in dry gear hobbing of 20MnCr5 case-hardening steel, 42CrMo4 tempered steel and EN-GJS-700-2 cast iron
    ( 2021)
    Troß, Nico
    ;
    Brimmers, Jens
    ;
    Bergs, Thomas
    The demand for higher power densities in gear applications leads to the use of high-strength materials. This poses a challenge for manufacturing technologies with regard to the machinability of these materials. Even though gear hobbing is one of the most common technologies for gear machining, only limited investigations on the machinability of high-strength materials have been carried out. In this paper, the machinability of different workpiece materials by gear hobbing under dry cutting conditions is investigated. The tool life and wear behavior of powder metallurgical high-speed steel PM-HSS S390 and sintered tungsten carbide - cobalt WC-Co K30 tools with an AlCrN coating were analyzed. 20MnCr5 case-hardening steel, 42CrMo4 tempered steel and EN-GJS-700-2 cast iron were machined using the fly-cutting trial as an analogy process for gear hobbing. To identify a respective target tool life of LT,10 = 10 m, the cutting speed was varied while the feed rate was defined based on the respective tool concept and cutting substrate. The experiments showed a good machinability of the soft state material 20MnCr5 with PM-HSS S390 tools up to a cutting speed of vc = 350 m/min. A machining of the high-strength materials 42CrMo4 and EN-GJS-700-2 resulted in high tool wear or catastrophic tool failure. Even at low cutting speeds of vc = 50 m/min, the target tool life LT,10 could not be reached. When using WC-Co K30 tools, tool lives of LT > 6 m and cutting speeds up to vc = 400 m/min were feasible when machining 42CrMo4 tempered steel. For the machining of EN-GJS-700-2 cast iron, high abrasive tool wear was observed, which led to short tool lives of LT < 4 m at cutting speeds above vc > 200 m/min. By reducing the cutting speed to vc = 100 m/min, a tool life of LT > 15 m could be achieved.