Abstract
The present work deals with the development of a strategy for the prevention of end crater defects in high-power laser welding of thick-walled circumferential welds. A series of experiments were performed to understand the influence of the welding parameters on the formation of end crater defects such as pores, cracks, root excess weld metal and shrinkage cavities in the overlap area. An abrupt switch-off of the laser power while closing the circumferential weld leads to a formation of a hole which passes through the whole welded material thickness. A laser power ramp-down causes solidification cracks which are initiated on the transition from full-penetration mode to partial penetration. Defocusing the laser beam led to promising results in terms of avoiding end crater defects. Cracks and pores in the overlap area could be effectively avoided by using defocusing techniques. A strategy for avoiding of end crater imperfections was tested on flat specimens of steel grade S355 J2 with a wall thickness of between 8 and 10 mm and then transferred on the 10 mm thick pipe sections made of high-strength pipeline steel API5L-X100Q.
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Acknowledgements
The authors also thank HIGHYAG Lasertechnologie GmbH, Kleinmachnow, Germany, for providing the welding optics with the MZ-collimator for the welding experiments.
Funding
This IGF-project Nr.: 19.565 N/DVS-Nr.:06.104 by the Forschungsvereinigung Schweißen und verwandteVerfahrene.V. (DVS), Aachener Str. 172, 40,223 Düsseldorf, has been funded by the AiF within the program for sponsorship by Industrial Joint Research (IGF) of the German Federal Ministry of Economic Affairs and Energy based on an enactment of the German Parliament.
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Gook, S., Üstündağ, Ö., Gumenyuk, A. et al. Avoidance of end crater imperfections at high-power laser beam welding of closed circumferential welds. Weld World 64, 407–417 (2020). https://doi.org/10.1007/s40194-019-00841-x
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DOI: https://doi.org/10.1007/s40194-019-00841-x