A new monitoring method for metal rust removal states in pulsed laser derusting via acoustic emission techniques

Abstract

Considering that the direct visualization and real-time control of the laser derusting is challenging mainly in virtue of traditional microscopic procedures, it is very difficult for operators to judge the complicated derusting conditions accurately. Acoustic emission (AE) monitoring could be a promising technique to assess the termination of rust removal process, avoid thermal damage of carbon steel substrate efficiently. The AE monitoring and high-speed camera were successfully integrated for reliable investigation of laser derusting mechanism. Dynamic removal characteristics and microscopic changes of rust layer observed and analyzed using AE signals and high-speed images are utilized for further improvement of the mechanism of rust removal by pulsed laser. Based on the spectrum analysis of Fast Fourier Transform (FFT), three characteristic frequency contents including 15˜35 kHz, 65˜85 kHz and 140˜160 kHz of the filtered root mean square (RMS) signals closely associated to laser source impacting on steel substrate or rust layer were determined respectively, which provides the observable AE features relating to the thermal damage of substrate surface. Direct correction between RMS signals and specific laser derusting parameters was established to realize the monitoring of the process of complete rust removal using two representative laser fluences. The FFT was carried out during the same period within 0.3 s in order to validate any changes in the frequency content of 15˜35 kHz relating to the rust removal effect.