Fraunhofer-Institut für Produktionsanlagen und Konstruktionstechnik IPK

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  • Publication
    Study on the transition behavior of the bulging effect during deep penetration laser beam welding
    ( 2022)
    Artinov, A.
    ;
    Meng, X.
    ;
    Bachmann, M.
    ;
    Rethmeier, M.
    The present work is devoted to the study of the transition behavior of the recently confirmed widening of the weld pool, known as the bulging effect, during high-power deep penetration laser beam welding of thick unalloyed steel sheets. A three-dimensional transient multi-physics numerical model is developed, allowing for the prediction of the bulge formation and the study of its temporal behavior. The model is generalized to account automatically for the transition from partial to complete penetration. Several experimental measurements and observations, such as drilling period, weld pool length, temperature, efficiency, and metallographic cross-sections are used to verify the model and assure the plausibility of the numerical results. The analysis of the calculated temperature and velocity distributions, as well as the evolution of the keyhole geometry, show that the formation of a bulging region strongly depends on the penetration depth of the weld. Based on the numerical results, the bulge is found to occur transiently, having its transition from a slight bulge to a fully developed bulging between penetration depths of 6 mm and 9 mm, respectively.
  • Publication
    Calibration of thermographic spot weld testing with X-ray computed tomography
    ( 2017)
    Myrach, Philipp
    ;
    Jonietz, Florian
    ;
    Meinel, Dietmar
    ;
    Suwala, Hubert
    ;
    Ziegler, Mathias
    The paper presents an attempt for the calibration of an active thermography method that is suitable for the non-destructive evaluation of spot welds. Nowadays, the quality of spot welds is commonly characterised by the application of random chisel tests, which are time consuming, expensive and destructive. Recently a non-destructive testing method by means of active thermography was proposed that relies on the fact that the mechanical connection formed by the spot weld also serves as a thermal bridge between the two steel sheets joined in the welding process. It is shown in this paper that this thermal bridge can be thermographically characterised by extracting a measure for the spot weld diameter and hence the quality of the spot weld. The determination of the absolute value of the diameter hereby relies on a calibration of the testing system, which is performed by means of X-ray computed tomography in this study. The experiments were carried out using different experimental approaches, namely transmission as well as reflection geometry wSetup in reflectionith laser illumination. A comprehensive evaluation of samples produced using different welding currents, hence different quality, was carried out in order to validate the thermographic results.