Hybrid laser-arc welding of laser- and plasma-cut 20-mm-thick structural steels

It is already known that the laser beam welding (LBW) or hybrid laser-arc welding (HLAW) processes are sensitive to manufacturing tolerances such as gaps and misalignment of the edges, especially at welding of thick-walled steels due to its narrow beam diameter. Therefore, the joining parts preferably have to be milled. The study deals with the influence of the edge quality, the gap and the misalignment of edges on the weld seam quality of hybrid laser-arc welded 20-mm-thick structural steel plates which were prepared by laser and plasma cutting. Single-pass welds were conducted in butt joint configuration. An AC magnet was used as a contactless backing. It was positioned under the workpiece during the welding process to prevent sagging. The profile of the edges and the gap between the workpieces were measured before welding by a profile scanner or a digital camera, respectively. With a laser beam power of just 13.7 kW, the single-pass welds could be performed. A gap bridgeability up to 1 mm at laser-cut and 2 mm at plasma-cut samples could be reached respectively. Furthermore, a misalignment of the edges up to 2 mm could be welded in a single pass. The new findings may eliminate the need for cost and time-consuming preparation of the edges.

Hybrid Laser-Arc Welding of Thick-Walled, Closed, Circumferential Pipe Welds

The application of hybrid laser-arc welding (HLAW) for joining closed circumferential welds is a challenge due to the high risk of forming a defective overlap area with a shrinkage void or solidification cracks in the material thickness. A series of HLAW experiments were performed to understand the development of a faulty overlap area when closing the circumferential weld. Welding trials on flat specimens and pipe segments were supported by numerical analyses in which the thermomechanical behavior of the welds in the overlap area was investigated. Different process control strategies were tested, including variations in defocusing levels and the overlap length. The newly developed HLAW head, including laser optics with a motor-driven collimation system, made it possible to defocus the laser beam during welding without disturbing the stability of the welding process. High-level defocusing of the laser beam of more than 40 mm relative to the specimen surface with a resulting beam diameter of > 2.9 mm, and in combination with a short overlap length of 15 mm, was promising with respect to the formation of a desired cup-shaped weld profile that is resistant to solidification cracks.

Double-sided Hybrid Laser-Arc Welding of 25 mm S690QL High Strength Steel

Hybrid Laser-Arc Welding (HLAW) technique is an enabler for the next generation high efficiency we lding, bu t in dustrial ad option ha s be en li mited du e to pr ocess complexity. Previously documented challenges with root cracks posed by incomplete penetration were significant; h owever, t his w ork p resents s uccessful w eld s amples p repared f rom S 690QL steel welded from two sides with a 16 kW disc laser. Weld travel speeds below 500 mm/min and weld line energies between 1.7 and 1.9 kJ/mm gave sound weld samples, evaluated for yield strength, elongation, hardness and Charpy-V toughness according to DS/EN ISO 10025-6:2004+A1. The results shown here indicate a significant i ncrease i n t he overall e fficiency of but t wel ds in high strength steels and further cement the HLAW process for high strength steels. It is shown that the consecutive nature of the weld procedure led to non-negligible interpass temperatures for the second weld.

Study on temperature- microstructure- stress fields of thick-walled plate welded by hybrid laser arc welding

The 25mm DH36 steel was welded by hybrid laser arc welding (HLAW), and a sequence coupled thermal-metallurgical-mechanical (TMM) model was developed based on SYSWELD. The temperature-microstructure-stress fields are predicted by simulation verified by experiment. The ratio between the arc and laser energy showed a significant effect on weld profile. The laser provided the main power and ensured deep penetration, and the arc power showed a dominant effect on the bead width of the hybrid weld during HLAW. For the hybrid welding of a thick-walled plate, the microstructure and thermal cycles varied along with the thickness. The weld profile and microstructure were experimentally characterized. The 3-pass welding procedure produced larger welding residual stress than the 9-pass welding procedure, and the process stability is poorer than the 3-pass welding process. Overall, numerical results matched well with experimental results.