Acoustic emission signal monitoring of water-jet guided laser drilling in nickel-based superalloys

Water-jet guided laser (WJGL) machining technology has been extensively applied in the fabrication of film cooling holes in turbine blades, owing to its inherent advantages such as focus-free delivery, extended working distance, and high machining precision. However, when machining thin-walled hollow structures, the laser may traverse the front wall and directly impact the rear surface, resulting in backside damage that compromises the structural integrity and service life of the component. To address this issue, acoustic emission (AE) sensing was employed as an in situ monitoring approach capable of capturing real-time signals generated by energy transfer and material removal events. In this study, AE monitoring was applied to the WJGL drilling process in a nickel-based superalloy with a focus on characterizing AE signal features with process parameters and ablation depth. Results reveal that AE signals exhibit pronounced nonlinear behavior during drilling. At the initial stage, signal amplitudes show significant fluctuations, then progressively stabilize as the hole deepens, reaching a peak of 83 dB. Upon jet breakthrough, the signal intensity sharply decreases to 54.4 dB. Complementary laser cutting experiments confirmed the sensitivity of AE responses to material removal dynamics. Based on the characteristic waveform jitter and sustained high peak amplitudes observed when the hole core remains attached, a diagnostic criterion was proposed for identifying incomplete core detachment. These findings provide valuable insights for real-time monitoring, damage suppression, and intelligent control of WJGL machining, advancing the high-quality and efficient manufacturing of turbine blade film cooling structures.