Research on the Controllability of Aircraft Skin Laser Paint Remove Based on Laser-Induced Breakdown Spectrum and Composition Analysis

Laser paint removal, as a branch of laser cleaning technology, will replace the traditional polishing and chemical paint removal technology to achieve the controlled paint removal of the aircraft skin surface. However, the process and quality of controlled paint removal depend on effective in-situ online monitoring technology. For the multi-paint layer on the surface of the aircraft aluminum alloy skin, LIBS technology is used to analyze the spectral and the component of characteristic elements of different paint layers and different paint thicknesses during laser paint removal. Based on signal interpretation, to establish the relationship between the paint layer and paint thicknesses of laser paint removal and the change of LIBS spectrum. And to realize the real-time monitoring and feedback control of the paint removal process and quality. The results show that the spectral peak of the characteristic elements (Fe, Ti) of the layer disappears when the topcoat or primer is completely removed in the process of layered removal. Once LIBS monitors the characteristic element Fe of topcoat at 501. 494 1 and 521. 517 9 nm Fe I spectral characteristic peak disappears, the topcoat has been completely removed at the same time. And when the characteristic element Ti of primer at 498. 173 0, 499. 107 0 and 521. 039 0 nm Ti I spectral characteristic peak disappears, determine primer has been completely removed. When the paint is removed in different thicknesses, the spectral peak strength of the paint characteristic element (Ca) decreases correspondingly with the decrease of the paint thickness or the increase of laser pulse. Until the paint thickness is 0 (completely removed) , the spectral peak of the paint characteristic element disappears, and the matrix characteristic element (Al) appears. By applying the LIBS spectral signal intensity changes of Ca I at 616. 217 0, 643. 907 0 and 422. 673 0 nm, the remaining paint thicknesses during laser paint removal could be monitored and further realizes Laser-based Thickness Controlled Paint Removal. In addition, combined with EDS and SEM testing and analysis, the feasibility of LIBS for aircraft skin laser paint removal process and effect monitoring, Laser-based Layered Controlled Paint Removal and Laser-based Thickness Controlled Paint Removalare verified. It shows that under the premise of not damaging the oxide layer of the substrate, by monitoring the characteristic element spectrum and composition change law of the topcoat and primer at the corresponding wavelength position, Laser-based Layered Controlled Paint Removal and Laser-based Thickness Controlled Paint Removal can be achieved.