研究目的
The development of a strategy for the prevention of end crater defects in high-power laser welding of thick-walled circumferential welds.
研究成果
A defocusing of the laser beam over 80 mm shows requested effects on the weld shape. A cup-shaped partial penetration could be generated. Cracks and pores in the mid-thickness could be avoided using this technique. A short outfeed length of about 15 mm has been found to be advantageous. The shrinkage cavity on the top surface could be remelted by a smoothing welding run using 2 kW laser power and a spot diameter of 4.3 mm on the top surface. The transfer of the results obtained on the flat specimens to circumferential welds on 10-mm thick pipes of grade X100Q could be realized with a defect-free overlap area.
研究不足
The welding equipment used does not allow further defocusing of the laser beam over the 80 mm, so it is recommended to eliminate the end crater shrinkage crack using a smoothing by means of a melting beam in thermal conduction mode.
1：Experimental Design and Method Selection
A series of experiments were performed to understand the influence of the welding parameters on the formation of end crater defects. Different strategies of the process heat management were used, including laser power ramp-down and defocusing techniques.
2：Sample Selection and Data Sources
Flat specimens of steel grade S355 J2 with wall thickness of 8 mm and 10 mm, and pipe segments made of high-strength pipeline steel API5L-X100Q with a wall thickness of 10 mm.
3：List of Experimental Equipment and Materials
High-power Yb:YAG disk laser TruDisk 16,002 with a maximum output power of 16 kW, an emission wavelength of 1030 nm and a beam parameter product of 8 mm × mrad. Laser-processing head BIMO with a MZ-collimator. Ophir Spiricon Beam Watch non-contact laser measurement device.
4：Experimental Procedures and Operational Workflow
The laser power ramp-down was applied before welding process end. The defocusing was applied in the last 15 mm of the weld length. The welding parameter were the laser power PL 9 kW and the welding speed vw 1.8 m min?1 for flat specimens, and laser power of 11.5 kW at a welding speed of 2 m min?1 for pipe segments.
5：Data Analysis Methods
The results were evaluated by visual inspection, X-ray examinations and metallographic investigations on macro sections.
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