Relationship between melt flows based on three-dimensional X-ray transmission in situ observation and spatter reduction by angle of incidence and defocussing distance in high-power laser welding of stainless steel

• Published in: Welding international Vol. 32; no. 7; pp. 485 - 496
• Main Authors: Kawahito, Yousuke, Nakada, Kouki, Uemura, Yousuke, Mizutani, Masami, Nishimoto, Kouji, Kawakami, Hiroshi, Katayama, Seiji
• Format: Journal Article
• Language: English
• Published: Cambridge Taylor & Francis 03-07-2018; Taylor & Francis Ltd
• Subjects: angle of incidence; Austenitic stainless steels; Beads; Defocusing; defocussing distance; Image transmission; Incidence angle; Laser beam welding; laser welding; Mirrors; Reduction; Spatter; Stainless steel; Steel plates; Three dimensional flow; three-dimensional X-ray transmission in situ observation; Tracers; Tungsten carbide
• ISSN: 0950-7116; 1754-2138
• DOI: 10.1080/01431161.2017.1346887

The objective of this research is to reveal relationship between melt flows and spatter reduction by angle of incidence and defocusing distance in partial penetration welding of an SUS304 stainless steel plate using a 6-kW power laser beam. In welding speeds from 50 to 250 mm/s, underfilled weld beads with spatters were obtained at more than 150 mm/s. According to the three-dimensional X-ray transmission in situ observation of melt flows at 150 mm/s in welding speed with tungsten carbide (WC) tracers, the melt flows achieved approximately 2.3 m/s in speed and made convex molten-pool surface behind a keyhole inlet grow higher, resulting in spattering over 0.1 mm in diameter. A 2 mm inner defocusing distance or a 20° angle of advance decreased the number of spatter over 0.1 mm in diameter by half or one-third in comparison with that at focal point and 0°. The X-ray transmission images demonstrate that the appropriate defocusing distance and angle of incidence made the speed of the melt flow decrease and the melt flow behind a keyhole inlet circulate, which led to not only suppressing the convex surface but also improving the frequency that the convex surface went back to the molten pool.