Behavior of vapor/plasma within the keyhole and above the workpiece during CO2 laser penetration welding

In this paper,a high-speed camera and an optical emission monitor were used to study the behavior of vapor/plasma during CO2 laser welding of SUS304 stainless steel. Results of optical emission from vapor/plasma show that two characteristic frequency bands exist,100-500Hz and 1500-3500Hz. At the same time,the changing images of vapor/plasma and bottom pool also confirm that there are two different fluctuation frequency bands. One of the frequency bands represents the characteristic of vapor/plasma within the keyhole,and it is within 167-500Hz. Another frequency band is within 1500-3500Hz,and it obviously derives from the shielding gas. Some factors may cause these frequency differences between the keyhole plasma and the shielding gas plasma. One of them is that the vapor/plasma pressure within the keyhole will increase slowly.