Real-Time Fast Fourier Transform Analysis of Acoustic Emission during CO2 Laser Welding of Materials

Abstract

Real-time fast Fourier transform (FFT) analysis of acoustic emission has been developed for monitoring laser welding processes. Significant differences in acoustic emission have been observed in conduction and keyhole processing regimes. The amplitude fluctuation of acoustic emission becomes intensified in the transition from conduction welding to keyhole welding. The integrated FFT power spectrum emission has been correlated to laser power, welding speed, and focusing parameters. These results suggest a simple way of monitoring the welding process. A simplified physical model has been developed to explain the fluctuation frequency. The predictions of this model are found to be in good agreement with experimental data.

A Study on the Monitoring of Laser Welding for S45C Steel Sheets Using Nd:YAG Laser with Continuous Waves

“…Y-L. Mae 등은 레이저 용접 중 실시간 FFT(Fast Fourier transform) 해석에 관한 연구에서 FFT 파워 스펙트럼의 방출은 레이저 출력, 용접속도 및 초점 변수와 관계가 있다고 설명하였다 (5,6) . 또한, Teresa Sibillano 등은 용접 모니터링에서는 플라즈마 와 스패터 광신호를 획득하여 비주기적인 과도현상을 해석하 기 위해서 필터함수(Filter Function), 웨이브렛 변환(Wavelet Transform) 등을 이용하여 용융풀의 크기와 스패터의 양을 검 출하는 알고리즘 연구를 수행 하였다 (7,8) .…”

Automatic detection of lack of fusion defects in CO2 laser gear welding

“…1 Precise placement of the microphone is generally not required as the sound waves emanate in all directions. These can be detected using an externally mounted microphone.…”

Wavelet analysis of acoustic emission signals and quality control in laser welding

“…[1][2][3] The AE signals are processed using fast Fourier transforms ͑FFT͒ for spectrum analysis. 4,5 There are also some reports on time-frequency analysis with short-time Fourier transform. 6,7 In theory, a signal must be time invariant for use of the FFT.…”