Fraunhofer-Institut für Produktionsanlagen und Konstruktionstechnik IPK

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  • Publication
    Investigation of liquid metal embrittlement avoidance strategies for dual phase steels via electro-thermomechanical finite element simulation
    ( 2022-06)
    Biegler, Max
    ;
    Böhne, Christoph
    ;
    Seitz, Georg
    ;
    Meschut, Gerson
    ;
    Rethmeier, Michael
    Modern advanced high-strength steel (AHSS) sheets used in automotive body construction are mostly zinc coated for corrosion resistance. The presence of zinc can cause cracking in steels due to liquid metal embrittlement (LME) during resistance spot welding (RSW). In combination with factors such as tensile strains, liquid zinc can lead to the formation of brittle, intergranular cracks in the weld and heat affected zone. While practical investigations to mitigate LME occurrence exist, the reason why a certain parameter might cause or prevent LME is often unknown. Numerical resistance spot welding simulation can visualize the underlying stresses, strains and temperatures during the welding process and investigate experimentally unmeasurable phenomena. In this work, a 3-dimensional electro-thermomechanical finite element approach is used to assess and investigate the critical parameters leading to LME occurrence. Experimentally observed crack sizes are correlated with the corresponding local strain rates and temperature exposure durations in the simulation. With this data, a map of LME occurrence over driving influence factors is drafted and discussed for effectiveness.
  • Publication
    The Influence of Electrode Indentation Rate on LME Formation during RSW
    ( 2022)
    Böhne, Christoph
    ;
    Meschut, Gerson
    ;
    Biegler, Max
    ;
    Rethmeier, Michael
    During resistance spot welding of zinc-coated advanced high-strength steels (AHSSs) for automotive production, liquid metal embrittlement (LME) cracking may occur in the event of a combination of various unfavorable influences. In this study, the interactions of different welding current levels and weld times on the tendency for LME cracking in third-generation AHSSs were investigated. LME manifested itself as highpenetration cracks around the circumference of the spot welds for welding currents closely below the expulsion limit. At the same time, the observed tendency for LME cracking showed no direct correlation with the overall heat input of the investigated welding processes. To identify a reliable indicator of the tendency for LME cracking, the local strain rate at the origin of the observed cracks was analyzed over the course of the welding process via finite element simulation. While the local strain rate showed a good correlation with the process-specific LME cracking tendency, it was difficult to interpret due to its discontinuous course. Therefore, based on the experimental measurement of electrode displacement during welding, electrode indentation velocity was proposed as a descriptive indicator for quantifying cracking tendency.
  • Publication
    Validierung von Methoden zur Vermeidung von Liquid Metal Embrittlement an realitätsnahen Prinzipbauteilen (IGF 21483 BG / P 1488)
    ( 2021)
    Meyerdierks, Martin
    ;
    Schreiber, Vincent
    ;
    Böhne, Christoph
    ;
    Seitz, Georg
    ;
    Jüttner, Sven
    ;
    Meschut, Gerson
    ;
    Rethmeier, Michael
    Ziel des Forschungsprojekts ist es, eine Korrelation zwischen Gleeble-Heißzug-Prüfverfahren und Widerstandspunktschweiß-basierten Prüfverfahren herzustellen. Es soll die Effektivität von Methoden zu Vermeidung von Liquid Metal Embrittlement an realitätsnahen Prinzipbauteilen bewertet werden. Weiterhin soll Kenntnis über Auswirkungen von LME Rissen auf das Tragverhalten von realitätsnahen Prinzipbauteilen gewonnen werden.
  • Publication
    Prevention of liquid metal embrittlement cracks in resistance spot welds by adaption of electrode geometry
    ( 2020)
    Böhne, Christoph
    ;
    Meschut, Gerson
    ;
    Biegler, Max
    ;
    Frei, Julian
    ;
    Rethmeier, Michael
    Advanced high strength steels are usually coated by a zinc layer for an increased resistance against corrosion. During the resistance spot welding of zinc coated steel grades, liquid metal embrittlement (LME) may occur. As a result, cracking inside and around the spot weld indentation is observable. The extent of LME cracks is influenced by a variety of different factors. In this study, the impact of the used electrode geometry is investigated over a stepwise varied weld time. A spot welding finite element simulation is used to analyse and explain the observed effects. Results show significant differences especially for highly increased weld times. Based on identical overall dimensions, electrode geometries with a larger working plane allow for longer weld times, while still preventing LME within the investigated material and maintaining accessibility.
  • Publication
    Investigation of liquid metal embrittlement of dual phase steel joints by electro-thermomechanical spot-welding simulation
    ( 2019)
    Frei, Julian
    ;
    Biegler, Max
    ;
    Rethmeier, Michael
    ;
    Böhne, Christoph
    ;
    Meschut, Gerson
    A 3D electro-thermomechanical model is established in order to investigate liquid metal embrittlement. After calibration to a dual phase steel of the 1000 MPa tensile strength class, it is used to analyse the thermo-mechanical system of an experimental procedure to enforce liquid metal embrittlement during resistance spot welding. In this procedure, a tensile stress level is applied to zinc coated advanced high strength steel samples during welding. Thereby, liquid metal embrittlement formation is enforced, depending on the applied stress level and the selected material. The model is suitable to determine and visualise the corresponding underlying stresses and strains responsible for the occurrence of liquid metal embrittlement. Simulated local stresses and strains show good conformity with experimentally observed surface crack locations.