Study on the periodic oscillation of plasma/vapour induced during high power fibre laser penetration welding

High power fibre lasers have recently received much attention because of their inherent advantages such as high output power, high beam quality, compact size, and flexible fibre delivery. Studies on the mechanism behind fibre laser welding systems may further promote their practical application. In this paper, high speed video observations were used to study the characteristics of the plasma/vapour induced during the bead-on-plate welding of ZL114 using a high power CW fibre laser. We also analysed the cause of the periodic oscillation of the plasma/vapour. The results revealed that plasma/vapour induced from high power lasers oscillate periodically at 450–600 μs cycles above the weld pool surface. The use of a shielding gas has little effect on the oscillation cycle. The plasma/vapour absorption is not the main reason for the periodical oscillation of plasma/vapour induced during fibre laser welding. The periodic oscillation of the plasma/vapour can be attributed to the oscillation of the keyhole.

► High speed video observations were used to study the characteristics of the plasma.
► Plasma can be divided into two parts: the keyhole plasma and the floating plasma.
► Plasma oscillates periodically at 450–600 μs cycles above the weld pool surface.
► Use of a shielding gas has little effect on the oscillation cycle.
► Reason of the periodic oscillation of plasma is the oscillation of the keyhole.