2009 Volume 27 Issue 2 Pages 64s-68s
Fiber laser has been received extensive attention in welding of thick section materials in terms of high power intensity and high beam quality. This paper investigated the influence of fiber laser welding conditions, including welding speed, beam spot size and defocused distance, on the weld bead geometry in welding of thick section stainless steels. The result showed that the beam spot size had significant influence on the penetration depth, and the penetration depth at 0.1 mm beam spot size was shallower than that at 0.2 mm beam spot size. The maximal weld penetration at 10 kW laser power and 0.3 m/min could be obtained at the defocused distance of about -7 mm. Wine-cup weld bead geometry with excessive wide bead surface was formed in range of low welding speeds (lower than 1 m/min). As a result, the decrease in welding speed induces considerable increase in bead width, but only slight increase in penetration depth. In order to obtain deeper penetration at low welding speed range, it is important to enlarge and deepen the keyhole opening and suppress the plume/plasma. Thus an ultra-deep penetration laser welding method, which is characterized by using a gas jet nozzle to modify the keyhole and melt flow behavior, was developed. With two high-speed CMOS cameras and X-ray transmission apparatus, the behaviors of the keyhole, the melt flow and the plume in gas jet assisted laser welding were observed. The effects of the gas jet parameters and welding conditions on the weld bead geometry were investigated. By adoption of the gas jet, the penetration depth was increased from 18.2 mm to 24.5mm in the conditions of the laser power of 10 kW and the welding speed of 0.3 m/min. Moreover, the instability of penetration depth induced by thermal lens effect was also discussed.
