Fraunhofer-Institut für Produktionsanlagen und Konstruktionstechnik IPK

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  • Publication
    Avoidance of End Crater Imperfections at High-Power Laser Beam Welding of Closed Circumferential Welds
    ( 2019)
    Gook, Sergej
    ;
    Üstündag, Ömer
    ;
    Gumenyuk, Andrey
    ;
    Rethmeier, Michael
    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 the imperfections such as pores, cracks, excessive root-side drop-through and shrinkage cavities in the overlap area. An abrupt switch-out 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 causes solidification cracks which are initiated on the transition from full-penetration mode to partial penetration. Strategies with a reduction of the welding speed shows a creation of inadmissible root sagging. Defocusing the laser beam led to promising results in terms of avoiding end crater imperfections. Cracks and pores could be effectively avoided by using defocusing techniques. A strategy for avoiding of end crater defects was tested on flat specimens of steel grade S355J2 with a wall thickness of 10 mm and then transferred on the 9.5 mm thick pipe sections made of high-strength steel X100Q.