The effect of surface condition on acoustic emission during welding of aluminium with CO₂ laser radiation

The fast Fourier transform spectrum of acoustic emission during CO₂ laser welding of Al 1100 shows frequency components in the 3-9 kHz range that can be identified with the presence of a keyhole and correlate with penetration. In addition, a study of the effect of anodization and surface pretreatment of Al 1100 with excimer laser radiation has shown that acoustic emission at 9-10 kHz arises from burning off of surface oxide. A comparison of these results with those predicted from simple thermal and fluid dynamical models yields good agreement with theory. These results indicates that acoustic emission over specific frequency ranges may be highly diagnostic of laser processing conditions.