Experimental study on laser layered removal of blue automotive paint based on optimal laser parameters

Achieving high efficiency and quality in laser paint removal relies on selecting optimal laser parameters. In this study, a 1064 nm pulsed laser with a pulse repetition frequency of 100 kHz was employed for layered paint removal experiments on blue automotive paint with a multi-coating structure (clear, color, mid, and epoxy primer coatings). The optimal pulse width for laser paint removal was determined to be ∼ 200 ns through an image binarization method from the five preselected values of ∼ 100 ns, ∼150 ns, ∼200 ns, ∼250 ns, and ∼ 300 ns. An area extrapolation method was used to analyze the laser ablation thresholds of the coatings relative to average laser power, classifying them into two groups: the upper group (clear and color coatings) and the lower group (mid and epoxy primer coatings), with optimal average laser powers of 14 W and 20 W, respectively. An image binarization method evaluated the effective laser paint removal speed across different spot overlap ratios for both groups. The results indicated that a 50 % spot overlap ratio was optimal for both groups, leading to the maximum effective laser paint removal speed. A laser-induced breakdown spectroscopy (LIBS) was used to monitor the Pearson correlation coefficient over successive laser paint removal cycles. The optimal number of laser paint removal cycles was 5 for the upper coating group and 7 for the lower coating group based on the maximum Pearson correlation coefficient. Under these optimized conditions, the laser paint removal efficiency for a 50 mm × 50 mm blue automotive paint sample reached 98.6 %, with a relative error of ± 0.41 %. The novelty of this work lies in the integration of image binarization, area extrapolation, and LIBS for laser parameter optimization, ensuring minimal damage to the underlying layers and improving precision.