Towards better understanding of hyperbaric fiber laser spot welding of metallic material

Abstract

The effect of hyperbaric environment on fiber laser spot welding (LW) of 304 stainless steel was explored. The laser power was 3 kW, the welding time was 0.2 s, and the defocus distance was 0 mm. When ambient pressure rose from 1 to 18 standard atmospheric pressures (atm): the intensity of spectrum signals of plasma above molten pool increased; the number of nano-sized metallic particles inside the beam path grew; in the initial stage of welding, the growth rates of the depth of molten pool and the height of plasma plumes separately reduced to be about 9.1 % and 40 % of those under 1 atm; the weld penetration was decreased to 20 % of that under 1 atm; on condition that the ambient pressure rose to 12 atm from 1 atm, the size of plasma plumes and the intensity of spectrum signals from plasma increased while the weld penetration declined. The main physical mechanism causing reduction of energy density when laser beams went through beams of nano-sized metallic particles was the absorption effect of nano-sized particles rather than their scattering effect. The results also showed that plasma plumes decreased after applying side assisting gas (AS) flow, and they were obviously deviated from the laser beam path, thus increasing the weld penetration to some extent.