Mechanism and threshold fluence of nanosecond pulsed laser paint removal

In this paper, the nanosecond pulse laser surface treatment of the waterborne anti-rust paint on HT250 gray cast iron was carried out. The area and depth of the per-pulse laser ablation paint layer were measured. The threshold of laser energy density was determined through the relations with ablation area and depth. The paint removal mechanism was discussed by analyzing the ablation features of the paint layer on laser cleaning. The features of the paint removal under various laser energy densities were characterized, and the process parameters in the experiments were investigated. The results showed that there were four thresholds and three kinds of mechanisms in the paint removal process with nanosecond pulsed laser. The ablation threshold of substrate was deepened on the laser parameters. The ablation processes were included thermal ablation, thermal vibration and paint ionization concurrently, respectively. The surface cracks and paint debris were observed at the edge of the cleaning path, which were ascribed to the vibration effect by laser. In addition, the vibration effect could significantly increase the width of paint removal. Paint ionization has also a significant influence on the substrate morphology. Paint ionization would have an obvious impact on the formation of the substrate morphology. It is desirable to fabricate approach to remove the paint layer without damaging the substrate under optimized laser parameters by nanosecond pulse laser.