Analysis of optical and acoustic emissions during CO2 laser welding of a stainless steel

Abstract

We have measured optical and acoustic emissions from a CO2 laser welding of 304 stainless steel to monitor the welding process. The optical emission of Fe atom was detected by a spectrometer with an optical fiber. The acoustic emission was collected by a microphone. The bead on plate welding was performed with a 5 kW CO2 laser with a 245 mm parabolic mirror and its power was changed from 2 to 5 kW.Amplitude of both the optical and the acoustic emissions fluctuated quickly. There were some peaks in fast Fourier transform (FFT) power spectra of the signals. The major peaks of the acoustic emission appeared around 2.8 kHz when the welding was keyhole-type. When the welding was heat conduction-type, the frequency peaks above 5 kHz in the acoustic emission became larger in comparison to that around 2.8 kHz. The frequency distribution of the acoustic emission changed corresponding to the welding types. Similar dependency of the frequency spectrum on the welding types was observed in the optical signal. This correlation is reproducible and would be useful for online monitoring and process control.We have measured optical and acoustic emissions from a CO2 laser welding of 304 stainless steel to monitor the welding process. The optical emission of Fe atom was detected by a spectrometer with an optical fiber. The acoustic emission was collected by a microphone. The bead on plate welding was performed with a 5 kW CO2 laser with a 245 mm parabolic mirror and its power was changed from 2 to 5 kW.Amplitude of both the optical and the acoustic emissions fluctuated quickly. There were some peaks in fast Fourier transform (FFT) power spectra of the signals. The major peaks of the acoustic emission appeared around 2.8 kHz when the welding was keyhole-type. When the welding was heat conduction-type, the frequency peaks above 5 kHz in the acoustic emission became larger in comparison to that around 2.8 kHz. The frequency distribution of the acoustic emission changed corresponding to the welding types. Similar dependency of the frequency spectrum on the welding types was observed in the optical signal. This cor...