Laser induced breakdown spectroscopy online monitoring of laser cleaning quality on carbon fiber reinforced plastic

Carbon fiber reinforced polymer (CFRP) has attracted extensive attention in the industrial field due to its advantages of light weight and high hardness. The use of laser to clean the epoxy resin film on the surface of the carbon fiber is beneficial to improve the bonding performance. Combined with laser-induced breakdown spectroscopy (LIBS) technology, an on-line monitoring system for laser cleaning is designed to monitor the quality of laser cleaning in real time. The laser used in the experiment is a fiber laser widely used in laser cleaning, which has high cleaning efficiency, flexible use, and can be processed in a multi-dimensional space. The system is coupled with the scanning galvanometer which can be cleaned dynamically in all directions. The function of fast, real-time and high-resolution on-line monitoring of cleaning quality is realized. In this paper, prior information such as element composition and LIBS spectrum of epoxy resin and substrate carbon fiber in CFRP materials were obtained, and the differences were compared and analyzed. The results shown that the LIBS technology was feasible to monitor the cleaning quality. Subsequently, the experiment tested the influence of the laser process parameters on the LIBS characteristic spectrum, and it was confirmed that the average spectral intensity value at the wavelength (588.819 nm) was positively correlated with the average laser power. After that, according to the measured LIBS characteristic strength value, three evaluation grades of cleaning quality were effectively delineated. The piecewise linear fitting method was used to solve the value range of LIBS mapped by different grades, and the key data such as the optimal cleaning parameter threshold were calculated. Finally, scanning electron microscope (SEM) was used to observe the morphological characteristics of samples after laser cleaning under different grades, confirming that the LIBS characteristic line could effectively characterize the quality of laser cleaning.