SFB 1153 Tailored Forming

  • SFB 1153 – Teilprojekt A2: Wärmebehandlung für belastungsangepasste Werkstoffeigenschaften von Tailored Forming-Komponenten
    Within the framework of the Collaborative Research Centre 1153 "Tailored Forming", heat treatment strategies for tailored forming components are developed in the subproject A2. The aim is a local adaptation of the material properties. In addition to this local adaptation, the heating and cooling processes over the entire process chain are also to be considered, thereby resolving conflicts of interest between forming and heat treatment parameters. Since the bond zone of the joining partners represents the main challenge, the analysis of their development (layer thickness, microstructural composition) is of particular importance in all process steps. In order to perform the heat treatment, a tempering arrangement based on induction heating and air-water spray cooling is developed (see Fig. 1). Following the hardening of the steel functional surfaces, a simultaneous heat treatment of the steel-aluminium compounds can be developed and analyzed using different process routes (Fig. 2)
    Year: 2015
    Funding: DFG
    Duration: 07/2015 - 06/2019

Ressourceneffizienz/Nachhaltigkeit

  • FOR1766 – Teilprojekt TP4: Hochtemperatur-Formgedächtnislegierungen – Von den Grundlagen zur Anwendung
    The research unit FOR1766 combines partners from Ruhr University Bochum, University Kassel, Ludwig-Maximilians-University München and Leibniz University Hanover. For many of the envisaged applications, damage evolution under cyclic thermal and/or mechanical load will govern the fatigue life of high-temperature shape memory alloys (HTSMAs). Thus, the focus of the project in Hanover is the functional and structural thermomechanical fatigue of HTSMAs. To analyse the mechanisms that lead to functional degradation, this subproject concentrates on the functional fatigue tests of Ti-Ta HTSMAs in isostress thermal cycling tests under tensile load conditions and also on the In-situ thermo-mechanical cycling experiments. To understand the structural fatigue processes, within this project, structural fatigue test under high cycle thermomechanical loading conditions and crack propagation test will be carried out. To gain a fundamental understanding of the dominating microstructural processes, both post-mortem and in-situ fatigue experiments in the neutron source will be conducted.
    Year: 2015
    Funding: DFG
    Duration: bis 10.2018
  • SPP 1640 – Teilprojekt A4: Elektrochemisch unterstütztes Fügen blechförmiger Werkstoffe
    This research project investigates the cold pressure welding of similar and dissimilar metals by incremental forming and inline electrochemical surface activation. The project intends to identify and analyse the mechanisms of cold pressure welding in order to improve current cold welding processes in terms of process flexibility and joint strength. The joining with electrochemical support (EUCF) is a new process that intends to cold pressure weld a broad range of metal pairs. Major innovations include the determined modification of the micro and macroscopic surface structure e.g. by the inline activation of metallic surfaces using electrochemical reactions (like oxide reduction and metal layer deposition). The course and result of the following pressure welding process is supported by a special tool set-up and an adapted incremental process control to ensure a sufficient bonding process with locally restricted high deformation ratios. The pressure welding process will be realized with support of robotic actuators and an incremental process control to allow both partial and fully joining of hybrid products/assemblies made from various semi-finished parts.
    Year: 2015
    Funding: DFG
    Duration: bis 31/12/18
  • Entwicklung vielkristalliner zweiphasiger CoNiAl-Formgedächtnislegierungen mit hoher funktioneller Stabilität
    Ziel des Projektes ist das Problem des Korngrenzenversagens in polykristalline Formgedächtnislegierungen zu überwinden. Die Strategie hierzu umfasst ein gezieltes Aufwachsen einer duktilen γ-Phase an den Korngrenzen und die Unterstützung einer reversiblen Umwandlung dieser Phase in ihre Tieftemperaturmodifikation (ε-Phase). Durch anschließende spannungsinduzierte Martensit-(SIM)-Alterung werden feinste folgende Ausscheidungen gebildet, die eine vollständige γ-ε-Umwandlung unterstützen.
    Year: 2021
    Funding: DFG
    Duration: 04/2021 – 03/2024

[uncategorized]

  • Influence of local microstructure on the formability of extruded composite profiles
    Subproject A1 focuses on the development of a compound extrusion process which enables the continuous production of hollow profiles consisting of aluminum alloys and steel. The extruded profiles serve as a semi-finished product used in a subsequent forging process to produce bearing bushes (subproject B2), and therefore, they demand special properties. Besides the challenging process development, special focus is laid on sufficient weld seam properties and on the formation of continuous material bonding between aluminum and steel. The case-hardened steel (20MnCr5) acts as the wear-resistant functional surface of the bearing bushes. As seen in figure 1, the steel is inserted laterally as a tube into the modular extrusion die, especially designed so that the tube does not undergo deformation. The aluminum wrought alloy EN AW-6082 is then extruded onto the entire circumference of the steel profile via Lateral Angular Co-Extrusion (LACE). The quality of the metal bonding is determined first by the character of the bonding surface such as the presence of oxide layers and the creation of juvenile metallic surfaces during deformation, and second, by the intermetallic phases formed in the diffusion zone. The aim of this project is to investigate the influence of the interphase properties on the subsequent forging process and whether the bonding strength can be improved by process-dependent structural properties e.g. texture of the aluminum components, or the mechanical properties of the weld seam. The influence of the process parameters such as temperature, pressure, and time on the diffusion process in the bonding area will be examined accordingly in a deformation dilatometer. The results will be used for a numerical simulation of the process in a macroscopic model. The design of the extrusion process will be determined by means of numerical simulation, aiming at the formation of compound profiles with an adequate thin interphase suitable for the subsequent forming process. The joining zone of the extruded compounds will be analyzed using light and scanning electron microscopy techniques. The gained insights will be applied for the benefit of the process design and for the validation of the model.
    Year: 2015
    Funding: DFG
    Duration: 07/2015 - 06/2019
  • Influence of local microstructure on the formability of extruded composite profiles
    Subproject A1 focuses on the development of a compound extrusion process which enables the continuous production of hollow profiles consisting of aluminum alloys and steel. The extruded profiles serve as a semi-finished product used in a subsequent forging process to produce bearing bushes (subproject B2), and therefore, they demand special properties. Besides the challenging process development, special focus is laid on sufficient weld seam properties and on the formation of continuous material bonding between aluminum and steel. The case-hardened steel (20MnCr5) acts as the wear-resistant functional surface of the bearing bushes. As seen in figure 1, the steel is inserted laterally as a tube into the modular extrusion die, especially designed so that the tube does not undergo deformation. The aluminum wrought alloy EN AW-6082 is then extruded onto the entire circumference of the steel profile via Lateral Angular Co-Extrusion (LACE). The quality of the metal bonding is determined first by the character of the bonding surface such as the presence of oxide layers and the creation of juvenile metallic surfaces during deformation, and second, by the intermetallic phases formed in the diffusion zone. The aim of this project is to investigate the influence of the interphase properties on the subsequent forging process and whether the bonding strength can be improved by process-dependent structural properties e.g. texture of the aluminum components, or the mechanical properties of the weld seam. The influence of the process parameters such as temperature, pressure, and time on the diffusion process in the bonding area will be examined accordingly in a deformation dilatometer. The results will be used for a numerical simulation of the process in a macroscopic model. The design of the extrusion process will be determined by means of numerical simulation, aiming at the formation of compound profiles with an adequate thin interphase suitable for the subsequent forming process. The joining zone of the extruded compounds will be analyzed using light and scanning electron microscopy techniques. The gained insights will be applied for the benefit of the process design and for the validation of the model.
    Year: 2015
    Funding: DFG
    Duration: 07/2015 - 06/2019
  • Influence of local microstructure on the formability of extruded composite profiles
    Subproject A1 focuses on the development of a compound extrusion process which enables the continuous production of hollow profiles consisting of aluminum alloys and steel. The extruded profiles serve as a semi-finished product used in a subsequent forging process to produce bearing bushes (subproject B2), and therefore, they demand special properties. Besides the challenging process development, special focus is laid on sufficient weld seam properties and on the formation of continuous material bonding between aluminum and steel. The case-hardened steel (20MnCr5) acts as the wear-resistant functional surface of the bearing bushes. As seen in figure 1, the steel is inserted laterally as a tube into the modular extrusion die, especially designed so that the tube does not undergo deformation. The aluminum wrought alloy EN AW-6082 is then extruded onto the entire circumference of the steel profile via Lateral Angular Co-Extrusion (LACE). The quality of the metal bonding is determined first by the character of the bonding surface such as the presence of oxide layers and the creation of juvenile metallic surfaces during deformation, and second, by the intermetallic phases formed in the diffusion zone. The aim of this project is to investigate the influence of the interphase properties on the subsequent forging process and whether the bonding strength can be improved by process-dependent structural properties e.g. texture of the aluminum components, or the mechanical properties of the weld seam. The influence of the process parameters such as temperature, pressure, and time on the diffusion process in the bonding area will be examined accordingly in a deformation dilatometer. The results will be used for a numerical simulation of the process in a macroscopic model. The design of the extrusion process will be determined by means of numerical simulation, aiming at the formation of compound profiles with an adequate thin interphase suitable for the subsequent forming process. The joining zone of the extruded compounds will be analyzed using light and scanning electron microscopy techniques. The gained insights will be applied for the benefit of the process design and for the validation of the model.
    Year: 2015
    Funding: DFG
    Duration: 07/2015 - 06/2019
  • Entwicklung eines 3D-Modells zur Beschreibung der Mikrostrukturentwicklung in Nickelbasis-Superlegierungen bei starker thermo-mechanischer und thermo-chemischer Kopplung
    [Translate to Englisch:] Forschungsgegenstand des Projektes ist die Untersuchung des Kriechverhaltens von Nickelbasis-Superlegierungen. In Kooperation mit dem Institut für Kontinuumsmechanik (IKM) soll ein Modell entwickelt werden, das das Verhalten der Mikrostruktur bei Kriechbelastung beschreibt. Dazu werden EBSD-Messungen vom Ausgangszustand und weitere Messungen während des Kriechens durchgeführt. Hierbei soll eine Stelle der Probe von zwei Seiten analysiert werden. Basierend auf den somit erhaltenen zweidimensionalen Ergebnissen wird zusammen mit dem IKM ein dreidimensionales Materialmodell entwickelt. Zusätzlich werden nach dem Bruch die Querschnitte der Probe in verschiedenen Abständen zum Bruch metallographisch untersucht. Dies soll die Entwicklung der Mikrostruktur während des Kriechens zeigen und weitere Informationen, z. B. über die Dichte und Verteilung von Poren während der Kriechdehnung, liefern.
    Year: 2016
    Duration: 01.07.2016 - 31.12.2017
  • Aluminiumlegierungen mit angepasstem Schmelzintervall für das prozessintegrierte Ausschäumen beim Strangpressen
    The aim of this project is to develop the basics for the direct foaming of hollow structures made of aluminum alloys by means of composite extrusion. The outer structural material of these components takes over force distribution, corrosion protection, as well as acting tensile forces, while the internal foam material increases the bending stiffness, damping properties, and energy absorption of the system. For instance, such extruded, foam-filled structures can advantageously be used in the automotive industry as crash profiles. Nevertheless, process-integrated foam-filled structures or foam structures with a dense cover layer are not yet used industrially in mass production, despite their superior property spectrum. This could be due to the limited freedom of design in the production of foam-filled components with dense cover layers, in addition to elaborate additional operations required during their manufacturing process, such as additional foaming, manipulation, and joining processes
    Year: 2017
    Funding: DFG
    Duration: 05/2017-01/2021
  • Herstellung und Applikation thermoplastumhüllter Lotpartikel für die löttechnische Fertigung mit pulverförmigen Hartloten AiF-Projekt
    Within the scope of this project, brazing powders coated with a thermoplastic sheath are examined. The purpose of the coating is to fulfill two tasks: On the one hand, the metallic particles are electrically insulated by their coating, so that it is possible to aplly them by means of electrostatic powder coating processes prior to brazing, which is a new method to aplly brazing powders. From a scientific-technical point of view, suitable thermoplastics have to be found and a simple and economical coating process for the brazing powder has to be developed. Substantial technical, economic and ecological advantages can be achieved compared to solvent based brazing pastes. Users of this technology include both brazin powder products manufacturers who are expanding their portfolio and users of brazing technology who are enabled to use the product for new economical solder application processes.
    Year: 2017
    Funding: AiF
    Duration: 01.02.2017-31.01.2019
  • Optimizing the stability of underwater stud welding of large dimensions for repair and maintenance measures
    The research objective is the development of a stud welding system for underwater use, as well as the qualification of underwater stud welding for divers and ROVs.
    Year: 2017
    Funding: AiF
    Duration: 01.10.2016 - 30.09.2018
  • Material-based quenching model for the simulation of wet underwater welding
    The research objective is the simulation of wet underwater welding with special consideration of the heat transfer to the water.
    Year: 2017
    Funding: AiF
    Duration: 01.04.2016 – 31.03.2018
  • Extending the process limits for further processing of rolled semi-finished products by analysing the cause-effect relationships during roller straightening
    The aim of this research project is to develop a prognosis model for the description of relevant cause-effect relationships in the straightening process of steel and aluminium semi-finished products. The further processing of rolled strips in forming or cutting processes requires a flat running-in state with controlled and homogeneous properties. These required properties are usually not given due to imperfections that occur during the manufacture of semi-finished products and transportation as coils. The straightening process makes it possible to flatten the incoming material and influence the sheet properties in a controlled manner by utilizing alternating bending operations. Since process-related inhomogeneities of the infeed material affect the material properties after the straightening process, a specific correction of the straightening process over the unwound semi-finished product length is necessary. By identifying all relevant cause-effect relationships, guidelines are to be derived within a forecasting model for plan straightening, which allow a maximization of the process limits in the respective subsequent production stage.
    Year: 2017
    Funding: AiF
    Duration: 04/2017 – 03/2019
  • Research project P1125 (AiF-IGF 19289N): Cryogenic treatment of tool steels to improve technological properties (Nanocarbide)
    Cryogenic treatment of tool steels increases toughness and wear resistance. The aim is to change the microstructure by precipitation of nanocarbides throughout the whole cross section (Figure 1). Integrating the cryogenic treatment in the heat treatment chain provides a substantial cost reduction as an alternative to coating and surface layer methods. This project will lead to a basic understanding of the efficiency of cryogenic treatment by investigating submicroscopic processes. These include microstructural investigations by means of scanning and transmission electron microscopy and mechanical tests.
    Year: 2017
    Funding: AiF
    Duration: 01/2017 – 12/2019
  • Investigation of combined influence of skin pass rolling and roller straightening of a thin sheet made of materials with different crystal lattice on microstructure, texture, static and fatigue strength
    Skin pass rolling and roller straightening represent the final operations in sheet production and decisively determine the resulting microstructural and mechanical properties of the products. In preliminary investigations, it was shown that the intensity of the influence of these forming operations depends inter alia on material lattice structure. Further investigation is required on the combined influence on sheet properties as a result of monotonous forming by skin pass rolling which induces material work hardening and cyclical forming by roller straightening, which could induce either work hardening or work softening. Since sheet metal parts are subject to not only static but also cyclical mechanical stresses in later operations the residual stress state is of essential significance in addition to work hardening or softening. Thus, a comprehensive material characterization is required concerning mechanical properties during static and cyclical stresses. The work programme of the planned project includes the analysis of changes in mechanical properties during static and cyclical stresses as well as the investigation of microstructure and texture of sheets during various skin pass rolling and roller straightening conditions including the s-shape enclosing the rolls. The scientific aim of the planned research project is the investigation of combined influence of monotonous forming during skin pass rolling and cyclical forming during roller straightening of sheets made of materials with different crystal lattices (DC01, Cu, α-Ti) on microstructure, texture, the level and sign of residual stresses, and the mechanical properties within the framework of static and cyclical experiments. The practical aim of the project is the development of an appropriate technology for production of sheets with load-adjusted microstructure, texture, and a high static and fatigue strength by a suitable combination of monotonous forming by skin pass rolling and cyclical forming by roller straightening conditions.
    Year: 2017
    Funding: DFG
    Duration: 01.10.2016-30.09.2019
  • Arc Welding of Titanium-Alloys
    Focus of sub-project B6 is the development of repair methods for compressor blisks made from titanium alloys based on arc processes. Quality maintaining regeneration is achieved by the combination of flux effects and application of seeding agents as well as by controlled additive build-up of structures. To enhance the functional properties of blade regions that were regenerated and/or are subject to erosion, a localized surface nitriding using a plasma arc process is part of investigations. Besides practical welding tests, work programme includes structural analysis, measurement of hardness and residual stresses, fatigue evaluation and the implications of observed material properties on the expected service life of regenerated blisks.
    Year: 2018
    Duration: 01.01.2018 bis 31.12.2021
  • Precision forging of cast preforms
    The technology of forging cast preforms (casting/forging) represents an alternative to the conventional production of steel components with complex geometries. The main aim of the planned investigations is to obtain information on the development of the mechanical and microstructural properties of the structure of the casting preform during forming and the identification of suitable process parameters.
    Year: 2018
    Funding: DFG
    Duration: 01/2018 – 12/2020
  • Influence of hgh current density impulses on the properties and microstructure of nickel-based superalloys
    The aim of the research project is the investigation of the influence of hight electric current pulses on the microstructure of single-crystal nickel-based superalloys. This includes the analysis of the variation of dislocation structure, the orientation and morphology of γ- and γ'-phases and the distribution of elements in the material.
    Year: 2018
    Funding: DFG
    Duration: 04/2015 – 03/2018
  • Residual stresses in brazed hybrid steel joints
    In many cases, e. g. in vehicle or plant construction, heating or energy technology, manufacturing processes based on brazing technique are applied. In this context many components made of high-alloy steels are produced which are brazed in vacuum or protective gas furnaces at temperatures above 900°C. Often joining of ferritic and austenitic steels is desiderable or even necessary. Due to different thermo-mechanical properties of the materials and the solder used, high amounts of residual stresses can occur, which considerably reduce strength in comparison with joints made of similar steel types. In this project residual stress states are analyzed and assessed in detail depending on material combinations, geometries of the joints and the process parameters applied furnace brazing operations. From the results, strategies will be derived and validated to achieve minimum residual stress amounts in brazed dissimilar joints. The main objective of the project is to develop appropriate constructions and brazing processes adapted to the steel combinations used for dissimilar joints to achieve minimum residual stress amounts. As a result, manufacturers should be able to produce reliable high-strength hybrid components made of different stainless steel qualities by appropriate brazing processes applying reliable and process routes.One can expect that especially ferritic stainless steel qualities, which up to now are hardly used in practice will gain increasing importance as construction materials.
    Year: 2018
    Funding: AiF-FOSTA
    Duration: 01.11.2016-31.10.2018
  • Cu-Al-composite braze metals
    With the aluminum bronzes copper alloys are known, which have a good temperature strength and a high corrosion and oxidation resistance. However, these alloys cannot be used as braze metals in furnace processes e.g. for brazing CrNi steels, since the high oxygen affinity of the aluminum leads to a passivation of the braze metal preventing it from wetting the steel surface. To solve this problem braze metal composites consisting of an aluminum core and a copper capping layer are used, wherein the braze alloy composition is adjusted by the ratio of the material thicknesses used. The desired copper-aluminum braze alloy is formed then "in situ" during the melting process of the composite. The composite geometry and the temperature control during furnace brazing then determine within wide limits the braze metallurgy and thus the technological properties of the resulting brazed joint. Objective of the project is to investigate these dependencies and to develop suitable aluminum-copper composite brazes and appropriate furnace brazing processes. The braze metal composites can be produced both as wires and as sheets, making them suitable for a variety of brazing applications. Both suppliers of braze materials and producer of brazed assemblies made of CrNi steels, which are required in automotive construction, in heating and air-conditioning technology or in apparatus construction in a wide variety of shapes and designs, can benefit from this.
    Year: 2018
    Funding: AiF-DVS
    Duration: 01.01.2018-31.12.2019
  • CRC871: Near net shape turbine blade repair using a joining- and coating hybrid process (Subproject B1)
    Components of aircraft engines and stationary gas turbines like turbine- and compressor blades (airfoils and vanes) are subjected to extreme conditions. To increase the life time of such components, maintenance, repair and overhaul (MRO) play a paramount role. The subproject B1 of the CRC871 develops and investigates a near net shape joining and coating hybrid process which allows to shorten the state of the art process chain of turbine blade repair significantly. Since the turbine blades taken into consideration in this subproject are components of high pressure turbines, the focus of this work lies on nickel based alloys. The shortening of this process chain is achieved by applying the nickel based filler-metal together with the hot gas corrosion protective coating (e.g. NiCoCrAlY alloys) and the thermal barrier coating (TBC) with aluminium as a bond coat onto the substrate using the thermal spray technology. The following material combination results: substrate/nickel based filler-metal/NiCoCrAlY/Al/TBC. Subsequently this coating systems is subjected to a heat treatment which represents a common brazing- and aluminising process. The working hypothesis of this research project is that a thermal coating and joining process can be transferred to a hybrid technology and to achieve qualitative as well as economic advantages at the same time.
    Year: 2018
    Funding: DFG
    Duration: 01/2018 – 12/2021
  • Influence of nitrogen in the brazing atmosphere on the creep resistance of corrosive loaded CrNi-steel joints brazed with nickel based filler metals
    The widespread use of nitrogen as a process or cooling gas sometimes leads to massive problems in the brazing of CrNi steels with nickel-base braze metals. A reduction of the corrosion resistance of the brazed joints are observed then, which is apparently related to the nitriding of the materials in the area of the joining zone. Within the scope of the research project, it is therefore intended to clarify to what extent and under which brazing process conditions nitrogen enrichment takes place in the brazed seam area and how this influences the corrosion behavior and also the lifetime of the brazed joints. Specifically, it is investigated which correlation exists between the degree of nitrogen enrichment and the selected process conditions during brazing, how the different nitriding degrees affect the electrochemical corrosion behavior of the brazed joints and what consequences the degree of nitriding and the resulting corrosion damage have on the durability of the brazed joints. The results are used to derive process conditions for furnace brazing, in which the consequences of nitrogenification can be avoided without having to forego nitrogen, which is very cost-effective and easy to handle in terms of safety compared to alternative process gases (argon, hydrogen).
    Year: 2018
    Funding: AiF-DVS
    Duration: 01.04.2016-30.09.2018
  • In-situ investigations of the physicochemical mechanisms of surface activation of stainless steels during heat treatment applying brazing-process-like conditions in reducing process gases
    The deoxidation of work piece surfaces in a furnace brazing process using reducing process gases is the precondition for its wettability with braze metal and determines the success and the quality of the resulting brazed joints. While the necessary thermodynamic conditions e.g. for the reduction of native oxidized stainless steel surfaces with hydrogen or monosilane are known, the kinetics of such reactions is not investigated up to now on the atomic scale. However, the latter is essential for a general understanding of the process and is the precondition for further developments in brazing technology. In this context, the use of monosilane doped nitrogen as cost efficient and resource saving alternative to hydrogen, which is state of the art in furnace brazing, is of mayor scientific and technologic interest. Scope of this project is the investigation of the physicochemical mechanism of surface deoxidation, when brazing stainless steels in a conveyor belt furnace using hydrogen and monosilane containing process gases. The experiments planned are expected to provide detailed information of the chemical reactions and surface conditions during brazing, which are essential for the advancement of fluxless brazing processes with regard to lower process temperatures, robust processes and demanding stainless steel specifications. Starting point of the project are thermodynamic calculations of possible reactions, for which analytical transport models of oxide layer formation are specified and adjusted for the actual problem. These theoretical considerations are tested by in situ analysis of surface reactions - also time resolved - covering typical process conditions in a conveyor belt furnace, in order to get kinetic information about changes in the surface region of stainless steels with respect to crystal structure, atomic coordination (bond distances, coordination numbers), chemical bonding and atomic diffusion. For this purpose TR-XRD (Time Resolved X-ray Diffraction) and time resolved EXAFS/XANES (Extended X-ray Absorption Fine Structure/ X-ray Absorption Near Edge Structure) measurements using synchrotron radiation are performed. The simulation of realistic furnace conditions during this measurements are carried out in a high temperature cell for X-ray experiments, which is manufactured specially for the requirements to be simulated. The mentioned X-ray measurements are performed at the DELTA synchrotron light source in Dortmund and at the Deutsche Elektronen-Synchrotron (DESY, Hamburg) On the basis of the performed measurements and complementary brazing experiments in a conveyor belt furnace with ex-situ analysis of the heat treated specimen a physical model will be developed, which takes into account all physicochemical aspects of surface changes observed in the simulation of the brazing processes.
    Year: 2018
    Funding: DFG
    Duration: 01.04.2014-31.12.2019
  • Selective thermally oxidated tool surfaces for dry deep drawing
    Friction and wear have significant influence on tool life in sheet metal forming. In this regard, ‎lubricants are generally used to extend the tool life. Since the use of these ‎lubricants does not correspond with the target of sustainable production, methods for ‎dry forming are investigated in the priority program 1676. Within the scope of this project, the production and the use of tool coatings, which ‎are produced by selective thermal oxidation, are investigated.‎ The oxidative heat treatments of the tool surfaces take place at a defined oxygen residual. Therefore the treatments are carried out under a protective gas atmosphere (nitrogen) and monosilane doped nitrogen, respectively. So it is possible to generate ‎oxide coatings with a defined chemical composition and thickness.‎ The investigation results from the first project period show that oxide layers ‎produced under certain process conditions have friction coefficients, that are ‎comparable to those measured on the tool surfaces after applying lubricants.‎ In the second phase of this subproject, an innovative heat treatment method has been ‎developed. Conventionally, a continuance heating process was used to create the oxide layers. This manufacturing method requires an increased processing time and an increased amount of process gases. In ‎comparison, the new heat treatment method deploys a tube furnace, which ‎allows the production of oxidised-coated specimens with reduced protective gas ‎consumption. ‎In addition, an inductive heating unit was installed in the heating system to decrease ‎process time d. Moreover, various surface modifications were ‎investigated in the second phase of the project including friction and wear ‎experiments. These, and further results from the numerical investigations carried out ‎in the first and second project phases are necessary to understand the approach of ‎dry metal forming researched and thus to ensure the industrial application of this forming ‎technology. This point, applying the gathered experience in ‎dry metal forming in industrial processeswill be the core of the research project in ‎its third phase, whereby a modular deep-drawing tool is going tobe built, which will be ‎equipped with oxidised mold inserts. By manufacturing different components with various geometries using the planned ‎tool system it is possible to increase the load collective on the generated oxide layers ‎successively and thus investigating the behaviour of the layer system in a ‎conventional deep-drawing process.‎ At the same time, the heat treatment process to produce the oxide layers will ‎be continually optimised. Furthermore, the developed numerical model, which was validated on test ‎specimens, will be deployed on the geometries investigated in this phase as well. ‎Finally, the recreating process of the layer system will be investigated, so that more ‎information about the tool life can be determined.‎
    Year: 2018
    Funding: DFG
    Duration: 01.01.2014 – 01.01.2020
  • Investigation and use of thermo physicochemical mechanism of surface deoxidation using silane-doped argon in low vacuum brazing processes
    The objective of the proposed project is the investigation and clarification of deoxidation mechanism of natural passivated steel surfaces in vacuum brazing processes, in order to understand and then optimize vacuum brazing of stainless steels. Firstly, analytical methods will be developed, which allow a surface-sensitive “in situ” analysis of metal surfaces during annealing of metal specimens using vacuum-furnace-like process conditions. The methods must tolerate variations of the heating conditions as well as a variation of the gas atmosphere concerning its composition and its pressure up to 1 mbar. Particularly the use of silane-doped Argon for realizing defined deoxidizing conditions is a major aspect of the investigations planned, since significant improvements for the brazing of stainless steels are expected from this gas mixture in a low vacuum process. The “in situ” investigations will be confirmed by vacuum brazing tests using similar process conditions. A vacuum furnace, which is equipped with a gassing system that allows for defined silane-argon-compositions up to 1 mbar within the furnace recipient, is used for tempering and brazing steel specimens with appropriate braze metals. From an analysis of the brazed specimen a correlation between the “in situ” investigations of surface deoxidation and the wetting behavior of brazes on the steel surfaces as function of the performed process conditions will be worked out. Furthermore the experimental data from „in situ“-measurements will be used to clarify the deoxidation mechanism and quantify the kinetics of the detected surface reactions. These data are the base for a physical model to be developed, which describes the thermodynamic and kinetic aspects of the observed surface reactions and shall allow for a prediction of optimal process conditions for vacuum brazing of particular difficult-to-braze stainless steels.
    Year: 2018
    Funding: DFG
    Duration: 01.12.2014-30.07.2019
  • Mechanisms of action of nanoparticles as novel grain refiners for thermomechanically highly stressed cast aluminium components
    The aim of the research project is the targeted analysis of the use of nanoparticles of different size and composition as grain refiners in silicon-containing aluminium casting alloys, as well as the quantitative and qualitative evaluation of the effect of the grain refining effect on the microstructure and the thermomechanical properties.
    Year: 2018
    Funding: DFG
    Duration: 05/2017 – 04/2020
  • Production of areas with reduced strength in press-hardened components by means of a tempering station
    The transfer project should adapt the methodology of a local temperature control of austenitized materials before or between individual forming steps for the specific setting of a desired microstructure in a practical application using the example of press hardening. Graded material properties are obtained in the press-hardened components based on locally adapted microstructures by employing the technology of a two-phase spray cooling process in collaboration with the project partner, Volkswagen AG. Press-hardened components that have regions with locally reduced strength show an increased ability to join and facilitate trimming. In the proposed transfer project, the microstructural adjustment should take place through a targeted pre-cooling on localized component areas before the actual press hardening process. A suitable heat control unit must be developed to design such a pre-cooling by means of two-phase spray and simultaneous temperature control of component regions, which should not cool down and must be kept at a temperature above Ac3. For this purpose, numerical simulation models and experiences from the ongoing project can be used. In the pre-cooled areas first a temperature in the range of bainite or pearlite transformation should be adjusted to achieve a bainitic microstructural transformation during the subsequent and uniform cooling in the press-hardening tool. Areas quenched from a temperature level above Ac3 undergo a martensitic transformation due to cooling in the press-hardening tool. As an example, possible difference in hardness due to different temperature control is shown in Fig. 1. The advantage of this procedure is that no locally tempered press-hardening tools are required and short holding times during hot stamping can be used. Ultimately, it should be verified whether the tempering station is practically useful for the local formation of different microstructures by means of local cooling and maintaining the local austenitized state of the sheets at the same time. At Leibniz Universität Hannover, the design of the tempering station and the hot stamping is carried out at the Institute of Forming Technology and Machines, and the development of the pre-cooling device and the microstructure characterization is carried out at the Institut für Werkstoffkunde (Materials Science).
    Year: 2018
    Funding: DFG
    Duration: 01/07/2017 – 30/06/2019
  • Innovative Mischbauweisen mit dünnwandigen Aluminiumdruckguss-Strukturen mittels Bolzensetzen und fließlochformenden Schrauben
    Aluminum casting components are becoming increasingly popular due to their specific weight, high stiffness, and individual geometries. A prerequisite for the use of these cast components in mixed structures with aluminum or steel sheets is the application of a suitable joining technique. Due to the design individuality of these components, there is often only a one-sided access to the joint area. Joining methods which allow one-sided joining of casted aluminum components are, for example, flow-drilling screwing or tack-setting. For these methods, the local joint stiffness is of decisive importance. However, for cast components, local joint stiffness can be very variable. For example, hollow areas present low stiffness, while joint areas between ribs often show increased values. Reduced joint stiffness complicate the joining process and lead to component deformation, gaps between the joining partners, and in hybrid joining, to a poorer adhesive bond. This is due to the joining forces introduced statically or abruptly during the joining process. To solve the described problem, a holistic approach to the component and joining areas design is pursued. This will allow, in an early stage of designing and production planning, to select the according joining processes for components with one-sided accessibility, and therefore, improve manufacturing planning. The project results can be used in the design of cast components in order to optimize them for one-sided joining processes. The sample component to be developed can be used by SMEs and OEMs in the early stages of product development to sample component stiffness and to investigate the influence of production related disturbances. Project partner: Universität Paderborn, Laboratorium für Werkstoff- und Fügetechnik (LWF)
    Year: 2018
    Funding: AiF
    Duration: 01.01.2017 - 30.06.2019
  • Reduction of hydrogen-induced cold cracking in wet underwater welding of higher-strength fine-grained steels by integrating austenitic weld metal into the welding sequence
    The research objective is the prevention of hydrogen-induced cold cracks in wet underwater welding of higher-strength fine-grained steels. By using austenitic weld metal, macroscopic hydrogen traps are introduced into the welding sequence, preventing the damaging effect of the hydrogen.
    Year: 2018
    Funding: AiF
    Duration: 12/2016 – 11/2018
  • Dynamic magnetic-data storage on thermal sprayed layers
    The aim of the project is the manufacturing and characterisation of thermal sprayed layers with magnetic properties to store data dynamically on the component’s surface. It will be examined if the field of application of established coating systems, such as hard coatings or corrosion protection (e.g. WCCo(Cr)), can be extended to magnetically store data. Additionally, the ferrimagnetic maghemite (ɣ-Fe2O3), which is not used as a spray material yet, should be examined as an alternative for thermal spray coatings. Based on these results, the next step of the project is the understanding and quantification of the magnetic properties of the manufactured thermal spray coatings.
    Year: 2018
    Funding: DFG
    Duration: 01/2017-12/2019