Univ. Prof. Dr. Ing.

Bergs, Thomas

Filters
Reset filters

Settings
Now showing 1 - 8 of 8
  • 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
    Machine learning-based predictive modeling of contact heat transfer
    ( 2021)
    Vu, Anh Tuan orcid-logo
    ;
    Gulati, Shrey
    ;
    Vogel, Paul-Alexander
    ;
    Grunwald, Tim
    ;
    Bergs, Thomas
    Heat transfer phenomena at the interface between two contacting solids are highly complex involving multiple influencing factors. Over the years, a large amount of experiments were carried out to determine the contact heat transfer coefficients between two dissimilar joint materials. However, there are still no existing theoretical or physics-based models that satisfactorily predict the contact heat transfer coefficients. By taking advantage of the existing data, in contrast, machine learning promises a powerful method, capable of predicting the contact heat transfer coefficients for different material pairs and contact conditions. This research introduces a robust machine learning-based model that succeeds in precisely estimating the heat transfer across the interfaces between glass and steel, a material pair widely used in hot forming of glass. The data used for training and validating the machine learning models were determined experimentally by means of infrared thermography. The datasets consisted of contact heat transfer coefficients with dependence on three factors - interfacial temperature, contact pressure, and surface finishes. Aim of this study is to analyze the prediction accuracy and interpretability of various supervised learning algorithms in order to realize the machine learning models that are able to capture the underlying physics governing the heat transfer phenomena at the glass-mold interface. Finally, the results were compared with those estimated by a theoretical model and a numerical simulation model. The comparison demonstrates enhancements in prediction accuracy enabled by the data-driven method. This study indicates accurate and efficient strategies for solving thermal problems in hot glass forming processes.
  • Publication
    Hartwalzen von Lagerringen zur Lebensdauersteigerung
    ( 2020-07-30)
    Jahnel, Kirk
    ;
    Hähnel, Sebastian
    ;
    Grunwald, Tim
    ;
    Bergs, Thomas
    Zur Steigerung der Lagerlebensdauer von Hybridwälzlagern hat das Fraunhofer Institut für Produktionstechnologie IPT gemeinsam mit Cerobear GmbH, Hegenscheidt-MFD (A Member of the NSH-Group) und Schmitz-Metallographie GmbH an der Qualifizierung und Implementierung des Verfahrens Hartwalzen in die Prozesskette zur Herstellung von Hybridwälzlagern gearbeitet. Durch die Induzierung von Druckeigenspannungen in die Lagerlauffläche konnte die Lebensdauer nachweislich erhöht werden. Die Arbeiten wurden im Rahmen des geförderten Forschungsvorhabens "Hartwalzen von Lagerringen" durchgeführt, das aus Mitteln des europäischen Fonds für regionale Entwicklung (EFRE) gefördert wurde.
  • Publication
    Modeling of thermo-viscoelastic material behavior of glass over a wide temperature range in glass compression molding
    ( 2020)
    Vu, Anh Tuan orcid-logo
    ;
    Vu, Anh Ngoc
    ;
    Grunwald, Tim
    ;
    Bergs, Thomas
    In glass compression molding, most current modeling approaches of temperature-dependent viscoelastic behavior of glass materials are restricted to thermo-rheologically simple assumption. This research conducts a detailed study and demonstrates that this assumption, however, is not adequate for glass molding simulations over a wide range of molding temperatures. In this paper, we introduce a new method that eliminates the prerequisite of relaxation functions and shift factors for modeling of the thermo-viscoelastic material behavior. More specifically, the temperature effect is directly incorporated into each parameter of the mechanical model. The mechanical model parameters are derived from creep displacements using uniaxial compression experiments. Validations of the proposed method are conducted for three different glass categories, including borosilicate, aluminosilicate, and chalcogenide glasses. Excellent agreement between the creep experiments and simulation results is found in all glasses over long pressing time up to 900 seconds and a large temperature range that corresponds to the glass viscosity of log (η) = 9.5 â 6.8 Pas. The method eventually promises an enhancement of the glass molding simulation.
  • Publication
    Tailored melt pool shape by dual laser beam LMD-w process
    ( 2020)
    Gipperich, Marius
    ;
    Riepe, Jan
    ;
    Day, Robin
    ;
    Bergs, Thomas
    Additive Manufacturing (AM) is a fast growing manufacturing market. Laser Metal Deposition (LMD) is a high deposition rate metal AM process mostly used for repair, cladding or manufacturing applications. The two commonly used LMD-processes are powder-based (LMD-p) and wire-based (LMD-w). While LMD-p offers high deposition rates up to 2 kg/h (compared to LMD-w with 1kg/h) the handling of powder in terms of health and safety as well as machine wear become important. Furthermore, the material efficiency (due to overspray) is lower compared to the LMD-w AM-process. This is where LMD-w offers advantages, but advanced concepts to improve the stability of the LMD-w process to the level of LMD-p are needed. In this presentation, an approach is investigated to stabilize the LMD-w process by combining continuous wave (cw) laser and low-power pulsed wave (pw) laser. Calorimeter-like absorption measurements as well as deposition experiments are carried out to understand the physical background of the dual laser process and how this setup helps to stabilize the process. Promising results were achieved showing the possibility to tailor the melt pool height and width by a factor of 1.5-2 and an increase of energy absorption by 20%. This leads to a new perspective for the LMD-w manufacturing process (3D part build up, cladding and repair) in many industry sectors such as mobility, energy and engineering.
  • Publication
    Interoperabilität als Erfolgsfaktor für die vernetzte, adaptive Produktion
    ( 2020)
    Kiesel, Raphael
    ;
    Pothen, Mario
    ;
    Arntz, Kristian
    ;
    Bergs, Thomas
    ;
    Schmitt, Robert H.
    Das Wertschöpfungspotential der digitalisierten Produktion in Deutschland ist unumstritten. Um dieses Potential auszuschöpfen ist die Interoperabilität aller Akteure elementar. Zum einen bedarf es einer organisatorischen Interoperabilität, welche die Rollen aller beteiligten Akteure definiert. Zum anderen ist eine semantische Interoperabilität, welche das Vokabular eindeutig festlegt, notwendig. Ein Ansatz für eine erfolgreiche Interoperabilität wird in diesem Artikel dargestellt.
  • Publication
    Tailored melt pool shape and temperature distribution by a dual laser beam LMD-w process
    ( 2020)
    Gipperich, Marius
    ;
    Riepe, Jan
    ;
    Day, Robin
    ;
    Bergs, Thomas
    Laser Metal Deposition (LMD) is a high deposition rate metal AM process used for repair, cladding or manufacturing. While wire-based LMD (LMD-w) offers several advantages such as high material efficiency and a safe and simple handling of the wire feedstock, advanced concepts are needed to increase the LMD-w process stability. In this presentation, an approach is investigated to stabilize the LMD-w process by combining a continuous wave (cw) laser and a low-power pulsed wave (pw) laser. Calorimeter-like absorption measurements as well as deposition experiments are carried out to understand the physical background of the dual laser process and how this setup helps to stabilize the process. Promising results were achieved showing the possibility to tailor the melt pool height and width by a factor of 1.5-2 and an increase of energy absorption by 20 %. This offers new perspectives for the LMD-w manufacturing process in many industry sectors.
  • Publication
    Influence of Glassy Carbon Surface Finishing on its Wear Behavior during Precision Glass Moulding of Fused Silica
    ( 2019)
    Grunwald, Tim
    ;
    Wilhelm, Dennis Patrick
    ;
    Dambon, Olaf
    ;
    Bergs, Thomas
    Laser technology has a rising demand for high precision Fused Silica components. Precision Glass Moulding (PGM) is a technology that can fulfil the given demands in efficiency and scalability. Due to the elevated process temperatures of almost 1400 C and the high mechanical load, Glassy Carbon was qualified as an appropriate forming tool material for the moulding of Fused Silica. Former studies revealed that the tools surface finishing has an important influence on wear behaviour. This paper deals with investigation and analysis of surface preparation processes of Glassy Carbon moulds. In order to fulfil standards for high precision optics, the finishing results will be characterised by sophisticated surface description parameters used in the optics industry. Later on, the mould performance, in terms of wear resistance, is tested in extended moulding experiments. Correlations between the surface finish of the Glassy Carbon tools and their service lifetime are traced back to fundamental physical circumstances and conclusions for an optimal surface treatment are drawn.