Univ. Prof. Dr. Ing.

Bergs, Thomas

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  • Publication
    An Analytical Model for Robot-Based Grinding of Axisymmetric Mold Inserts Using a Rotary Unit
    ( 2022)
    Tamassia, Eugenio
    ;
    Hähnel, Sebastian
    ;
    Pini, Fabio
    ;
    Grunwald, Tim
    ;
    Bergs, Thomas
    ;
    Leali, Francesco
    The grinding of mold inserts used for injection molding aims to improve the surface roughness according to precise quality standards. The insert surface must also have a surface topography that facilitates the release of the plastic material at the end of the injection process. In particular, fine machining lines must be parallel to the extraction direction from the mold to avoid the sticking of plastic material and subsequent surface damages compromising the functionality of the finished product. However, this step in the production chain is most often conducted manually. This paper presents an analytical model to grind a truncated cone-shaped mold insert for the mass production of plastic cups. The automated solution consists of a flexible robotic system equipped with a rotating external axis to improve the accessibility of the tool to the surface to be machined. The tool path programming requires the development of an analytical model considering the simultaneous mot ion of the insert and the robot joints. The effectiveness of the developed model is evaluated in terms of final surface quality, grinding lines direction, and total process time. The automated strategy developed can be easily implemented with machine tools and applied to inserts with different axisymmetric geometries.
  • 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
    Surface Modification of Inconel 718 by Robot-Guided Centrifugal Finishing and Vibratory Finishing
    ( 2022)
    Ohlert, Marius
    ;
    Prinz, Sebastian
    ;
    Barth, Sebastian
    ;
    Bergs, Thomas
    The main task of mass finishing processes is the significant reduction of the surface roughness of a workpiece. Since robot-guided centrifugal finishing has a material removal rate up to Q''w<500mm/h, it is able to reduce the surface roughness in a shorter process time than vibratory finishing. Furthermore, robot-guided centrifugal finishing is a promising manufacturing technology to induce residual compressive stresses even for high-temperature materials, such as Inconel 718. In order to show the potential of robot-guided centrifugal finishing as a surface modification process, experimental tests were carried out. Within the experimental tests, Inconel 718 was machined by vibratory finishing and robot-guided centrifugal finishing. By using robot-guided centrifugal finishing the maximum induced residual compressive stress was 58% higher compared to vibratory finishing. The findings were derived from the difference in terms of transfer of the kinetic energy between the abrasive media and the workpiece in robot-guided centrifugal finishing and vibratory finishing.
  • 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
    Tool geometry analysis for plunge milling of lead-free CuZn-alloys
    ( 2021)
    Baier, Stefan
    ;
    Kokozinski, Lukas
    ;
    Schraknepper, Daniel
    ;
    Bergs, Thomas
    Plunge milling is a critical process step in mass manufacturing of rectangular shapes in electrical connector components. These shapes are manufactured by drilling a pilot hole and subsequent plunge milling with a radial offset (pitch) one or more times. The plunged cavity serves as guidance for the final broaching cut. In light of new legislative initiatives, the electronics industry is forced to use lead-free Cu-Zn-Alloys for mass manufacturing of these connectors. The plunging tool is deflected due to the higher cutting forces experienced in machining of lead-free CuZn-alloys in comparison to alloys with lead. This results in an offset of the milled cavity and negatively impacts tool guidance in the subsequent broaching process. Therefore, the geometric tolerances cannot be met. In this paper, the effect of tool geometry and cutting parameters on the workpiece geometry in plunge milling is investigated. The effect of the microstructure of the work-piece materials CuZ n37, CuZn42 and CuZn21Si3P on the tool deflection and cutting force components is examined. The tools used vary regarding the design of the corner in terms of the corner chamfer and the inner shaft thickness. Friction between chips in the tools inner flutes and the cavity walls reduced workpiece accuracy. Improvements were achieved by reducing the width of the cutting corner chamfers, using large inner flutes and applying low cutting parameters.
  • 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
    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
    Investigation of the micro hardness at the cut surface of fine blanked parts with variation of sheet material and cutting temperature
    ( 2021)
    Weiser, Ingo Felix
    ;
    Feuerhack, Andreas
    ;
    Bergs, Thomas
    Fine blanking is a production technology of high importance especially for the automotive industry. As a procedure of sheet metal separation, it is possible to produce complex parts in a single stroke. As a difference to conventional punching, the cutting surface of fine blanked parts can often be used as a functional surface without further process steps. However, fine blanking as a forming process changes the microstructure of the metal sheet to a higher extend than cutting or machining processes. Due to this, it is of utmost importance to investigate the cause-effect-relations between the fine blanking process parameters and the resulting properties of the fine blanked part. Especially the condition of the cut surface as an important quality criterion has to be investigated. The quality characteristics of the cut surface of fine blanked parts are often subject of investigations. In addition, it would be of importance to investigate how the material properties in the shear zone are changed by the fine blanking process. This on one hand in turn can enable conclusions to be drawn about possible punch wear. If, on the other hand, hardening of the cut surface takes place as a result of fine blanking, then this could have a positive influence on the application properties of fine blanked components. Thus, an experimental fine blanking investigation of the micro hardness of the cutting surface has been made with variation of steel material and cutting temperature. It could be demonstrated that the micro hardness increases in direction towards the burr. This is independent on material and cutting temperature.
  • Publication
    Manufacturing technologies for fir tree slots: A technological and economic evaluation
    ( 2021)
    Heidemanns, Lukas
    ;
    Seelbach, Tobias
    ;
    Küpper, Ugur
    ;
    Seimann, Martin
    ;
    Bergs, Thomas
    Fir tree slots in engine disks pose a great challenge to the production process, especially due to the use of increasingly filigree geometries. Broaching with high-speed steel (HSS) as cutting tool material has been established as the state of the art process. However, this manufacturing process obtains the disadvantages of high tool costs and long waiting times in case of geometry adaptations. Alternative manufacturing technologies, namely electrochemical machining (ECM) and wire electrical discharge machining (WEDM) offer the potential to replace broaching. Because of their removal mechanism being independent of the mechanical properties of the material, these processes are not hindered by increasingly higher thermomechanical material properties. Furthermore, the tool in WEDM is not specific to geometry, allowing fast adaptations. Nevertheless, the technology specific white layer may reduce the mechanical integrity of the engine disk. ECM in contrast has no negative impact on the rim zone of the workpiece but the tool is still specific to the slot geometry. Consequently, this paper experimentally investigates the three different manufacturing technologies in order to evaluate their capability to manufacture fir tree slots with respect to geometric accuracy and surface integrity. Subsequently, the technology specific manufacturing costs are considered to outline the economic potential of each process while taking into account the influence of the batch size.
  • Publication
    Geometry model and approach for future blisk LCA
    ( 2021)
    Fricke, Kilian
    ;
    Gierlings, Sascha
    ;
    Ganser, Philipp
    ;
    Venek, Tommy
    ;
    Bergs, Thomas
    Air traffic is expected to double over the next 20 years and Flightpath 2050 targets to a 70 % reduction of CO2 and a 90 % reduction of NOx. Optimization of future aircraft engines often is dominantly driven by a focus on the reduction of fuel burn and emissions during operation. To identify additional environmental improvement potential a full Life Cycle Analysis (LCA) shall be aspired also including Materials, Processes and Resources, Manufacture and Production, Lifetime Services as well as Reuse, End-of-Life and Recycling. Core engine components, for example integral rotors, are comprised of Titanium- or Nickel-alloys and require complex manufacturing processes. A geometry design model of a compressor blisk is introduced which is employed as basis for a future LCA approach focusing on materials, processes and resources as well as manufacture and production. The model is a carrier for challenging manufacturing features such as large blade twist, high aspect ratio and small blade gaps. In addition to the geometry model, a first set of multiple technology scenarios and their process chains will be introduced which will serve as base for a future LCA.