抄録
In this study, the effects of the ring diameter of a ring-shaped beam on keyhole behavior and spatter generation mechanisms during bead-on welding of stainless steel（SUS304） were investigated. First, the relationship between penetration depth, penetration ratio, keyhole diameter and spatter generation was investigated using a single beam and ring-shaped beams with ring diameters of ϕ 440, ϕ 800 and ϕ 1000 μm formed by a beam-splitting diffractive optical element （DOE）. The single beam had the deepest penetration depth. Among the ring beams, the ϕ 440 μm ring-shaped beam had a better penetration ratio than the other ring-shaped beams. The number of spatters was several hundred for a single beam at any welding speed. On the other hand, with the ring-shaped beam,
the spatter suppression effect was confirmed for all ring diameters. In particular, when a ϕ 440 μm ring-shaped beam was used, the number of spatters was the lowest and the keyhole diameter reached a maximum of 620 μm. The keyhole welding phenomenon on the stainless steel edge surface was observed through quartz glass. In a single beam, spatter was observed when a protrusion formed on the keyhole rear wall ascended toward the keyhole aperture at a high speed of 1100 mm/sec. At the ϕ 1000 μm ring-shaped beam, the protrusion rise rate reached 735 mm/sec, and no spatter occurred. At this time, the molten pool formed around the keyhole by the ring-shaped beam was thought to act as a relaxation layer, contributing to a decrease in the rise rate of the protrusion within the keyhole and to the relaxation of shear stresses on the keyhole wall. With a ϕ 440 μm ring-shaped beam, no protrusions formed on the keyhole inner wall, and the internal shape of the keyhole was maintained. This is thought to be due to an increase in the power density of the ring part, which led to a greater amount of metal vapor generated inside the keyhole. Consequently, the keyhole
diameter expanded and the shape inside the keyhole stabilized.
