Laser cleaning of white composite automotive paint layers using online monitoring methods

To effectively remove composite automotive paint layers using laser cleaning while avoiding substrate damage, selecting optimal laser parameters through online monitoring is essential. A 1064 nm pulsed fiber laser with 100 kHz repetition rate and 150 ns pulse width was used to clean a white composite automotive paint layer (WCAPL) composed of clear, base, intermediate, and epoxy primer coatings. The variation in laser ablation thresholds of the WCAPL and the phosphate layer on the substrate was analyzed as a function of average laser power using an area extrapolation method. Based on these thresholds, the coatings were divided into two groups: outer coating combination (OCC) consisting of clear and white color coatings and inner coating combination (ICC) consisting of mid and epoxy primer coatings. Charred residue rates were also evaluated using area extrapolation, while an image binarization method assessed the correlation between the effective laser cleaning speed and the spot overlap rate. Laser-induced plasma spectroscopy measured the changes in elemental peak intensity with the number of laser cleanings. The optimal laser power, spot overlap rate, and number of laser cleanings for the OCC (14 W, 50%, five times) and the ICC (20 W, 50%, seven times) were identified. These settings result in a laser cleaning efficiency of up to 98.9% for the WCAPL without substrate damage. It is shown that the single-parameter experimental path “average laser power → spot overlap ratio → number of laser cleanings” proved effective in identifying optimal laser settings for high-quality, efficient removal of composite automotive paint layers, ensuring both safety and performance.