Fraunhofer-Institut für Produktionsanlagen und Konstruktionstechnik IPK

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  • Publication
    Method for defect-free hybrid laser-arc welding of closed circumferential welds
    ( 2021)
    Gook, Sergej
    ;
    Üstündag, Ömer
    ;
    Gumenyuk, Andrey
    ;
    Rethmeier, Michael
    This paper presents investigation results of a process for defect-free hybrid laser arc welding (HLAW) of closed circumferential welds. The process aims to avoid weld imperfections in the overlap area of a HLAW circumferential weld. A process control strategy for closing the circumferential weld was developed to achieve a defect-free overlap region by controlling the solidification conditions at the end of the weld. The controlled heat flow is achieved by adjusting the parameters of both welding processes involved, the laser beam as well as gas metal arc welding (GMAW) process. Experimental investigations were carried out on 12 mm to 15 mm thick tube sections. The influence of process parameters such as the laser power ramp, the change in magnification scale and the defocusing of the laser beam on the solidification conditions at the end of the circumferential weld was investigated to find an optimum strategy for ramping out the process energy. Within the framework of the experimental studies, it was demonstrated that defocusing the laser beam in the range between 60 mm and 100 mm over a short run-out area of the weld of approximately 15 mm led to a significantly better weld formation in the overlap area. A favorable cup-shaped weld shape could be achieved without a tendency to crack. The laser optics with a motor-driven lens system made it possible to increase the laser beam diameter without changing the position of the GMAW arc relative to the component surface.
  • Publication
    Hybrid laser-arc welding of thick-walled pipe segments with optimization of the end crater
    ( 2020)
    Üstündag, Ömer
    ;
    Gook, Sergej
    ;
    Gumenyuk, Andrey
    ;
    Rethmeier, Michael
    The study deals with the application of the high-power hybrid-laser arc welding process on up to 15 mm thick pipe segments with the intention to avoid end crater imperfections during closing of the circumferential welds, where the pipes were turned during welding in 1G- and 2G-positions. Different techniques such as laser power ramp-down, abrupt switch-off of the laser power and change of the magnification of the laser spot diameter and defocusing of the laser beam relative to the workpiece were tested to remove the laser energy from the process. It could be shown that a high defocusing of the optic system above 40 mm with a resulting beam diameter > 2.9 mm in a short overlap length of approx. 20 mm leads to the formation of a cup-shaped weld seam, which is preferred for avoidance of cracks and pores in the end crater. A laser optics with motor-driven lens system was used for the welding experiments to defocuse the laser beam without changing the position of the arc.
  • Publication
    Avoidance of end crater imperfections at high-power laser beam welding of closed circumferential welds
    ( 2020)
    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 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.