LIBS Monitoring and Analysis of Laser-Based Layered Controlled Paint Removal from Aircraft Skin

Abstract

Reliability and controllability of selective removal of multiple paint layers from the surface of aircraft skin depend on effective online monitoring technology. An analysis was performed on the multi-pulse laser-induced breakdown spectroscopy (LIBS) on the surface of the aluminum alloy substrate, primer, and topcoat. Based on that, an exploration was conducted on the changes of the characteristic peaks corresponding to the characteristic elements that are contained in the topcoat, primer, and substrate with different layers of a laser action, in combination with analysis of microscopic morphology, composition, and depth of laser multi-pulse pits. The results show that the appearance and increase of the characteristic peak intensity of the Ca I at the wavelength of 422.7 nm can be regarded as the basis for the complete removal of the topcoat; the decrease or disappearance of the characteristic peak intensity can be regarded as the basis for the complete removal of the primer. Al I spectrum at the wavelength of 394.5 nm and 396.2 nm can be adopted to characterize the degree of damage to the aluminum alloy substrate. The feasibility and accuracy of the LIBS technology for the laser selective paint removal process and effect monitoring of aircraft skin were verified. Demonstrating that under the premise of not damaging the substrate, laser-based layered controlled paint removal (LLCPR) from aircraft skin can be achieved by monitoring the spectrum and composition change law of specified wavelength position corresponding tothe characteristic elements that are contained in the specific paint layer.

Research on online monitoring of aircraft skin laser paint removal thickness using standard curve method and PCA-SVR based on LIBS

“…25 Furthermore, from Fig. (9), it can be inferred that around the boundary of the paint layer (45 mm), the data points exhibit a distinct regular distribution according to the paint layer structure, meeting the segmented curve tting. The main reason for the segmented tting is that the boundary layer at a paint thickness of 45 mm represents the junction between the topcoat and the primer.…”

“…Research on high-frequency laser paint removal LIBS online monitoring primarily focuses on analyzing the variation patterns of characteristic element emission spectral lines to assess the state or effectiveness of laser cleaning. For instance, research teams such as Yang Wenfeng from Civil Aviation Flight University of China, 9 Deng Guoliang from Sichuan University, 10 Sun Lanxiang from Shenyang Institute of Automation, Chinese Academy of Sciences, 11 and Tong Yanqun from Jiangsu University, 12 have utilized the evolution patterns or trends of LIBS characteristic spectral line intensities as criteria for qualitative assessment of paint layer cleanliness or effectiveness. However, to achieve precise paint removal and avoid substrate damage, it is imperative to strictly control the paint removal thickness.…”