Abstract
Light emission in high-power laser welding has been detected by a multi-photosensor system. This system can discriminate between the light intensities emitted from the plume, keyhole opening, and finger parts of a keyhole. Bead-on-plate welding of thick plates was performed with a 20 kW CO2 laser at different laser powers and welding speeds. The results showed poor correlation between time-averaged light emission and experimental penetration depth. This is because the light emission from the keyhole opening is much larger than that from the finger part. The light emission's power spectrum indicated that light emission from the finger part was higher than 200 Hz, whereas the light emission from the plume and keyhole opening was less than 200 Hz. A simple formula has been derived to predict the penetration depth on the basis of frequency analysis, and this prediction agrees well with the experimental penetration depth at various laser powers and welding speeds.
