Frequency analysis of optical and acoustic emissions during butt welding by CW YAG laser

Abstract

We have applied Fast Fourier Transform analysis to optical and acoustic emissions during bead-on-plate welding with CO₂ and YAG lasers in our previous study. Some characteristic peaks in their frequency spectra were correlated with the bead profile. In this study, we have done butt welding of mild steel and stainless steel with 4 kW CW YAG laser. The optical and acoustic emissions during the welding were measured and the frequency spectra were analyzed. The major frequency peaks of the acoustic emission appeared in the range of 1 - 4 kHz and 6 - 7 kHz, although there were some additional peaks up to 40 kHz. These strong peaks appeared always in deep penetration mode welding. However, these peaks became small when the penetration depth became shallow by increasing the welding speed. We have shown that the acoustic spectrum of deep penetration mode welding is different from that of shallow penetration mode welding. The deference of the frequency spectrum should be useful in the development of a feedback system for control of weld quality.