基于热烧蚀效应的激光清洗仿真模型研究(特邀)

为研究在基于热烧蚀效应的激光清洗中激光参数对清洗效果的影响，根据热烧蚀效应原理、傅里叶热传导方程以及能量守恒定理，使用有限元分析软件建立了热烧蚀动态能量守恒的二维激光清洗仿真模型。在该模型中使用了虚拟第三类边界条件，将薄层-基底系统中的激光烧蚀热功率密度与被烧蚀污渍层边界的法向移动速度进行关联，实现了污渍层烧蚀潜热消耗量与激光烧蚀能量之间的动态能量守恒，明确了质量损失与能量消耗的数学关系，使所建立的模型更加理论自恰和精确可靠。利用该模型理论分析了光斑吸收功率、光斑直径、扫描速度以及扫描能量密度对清洗效果的影响，结果表明：污渍平均残留厚度随光斑吸收功率和扫描能量密度增大而减小，且减小的速率会逐渐变慢，当激光功率过大时，基材会出现损伤；污渍平均残留厚度随光斑直径和扫描速度的增大而变大，但减小光斑直径和扫描速度会降低清洗效率。提出了根据污渍层物性参数与扫描能量密度的对应关系优化激光参数的方法，并对非平整表面污渍层进行了多次不间断扫描的仿真分析，得到了清洗效果随扫描次数的变化规律。该研究结果对激光清洗设备的方案设计、优化改进和使用选型具有一定的指导意义。

Simulation model of laser cleaning based on thermally-induced ablation effects (invited)

In order to study the influence of laser parameters on the performance of laser cleaning based on thermal ablation effects, considering the working mechanism of thermally-induced ablation, Fourier heat conduction equation, and energy conservation theorem, a finite element analysis (FEA) software is used to establish a two-dimensional laser cleaning simulation model of dynamic energy conservation during the thermal ablation. In the simulation model, there is a mathematical relationship between the laser ablation intensity of the thin layer-base system and the normal velocity of the paint layer boundary, by using the virtual Robin boundary condition in the Fourier heat conduction equation. The simulation reflects the dynamic conservation of energy between the laser ablation energy and the latent heat consumption inside paint layers, which confirms the mathematical relationship between the mass loss and the energy consumption, and the simulation results become more precise and reliable. Such a simulation model is used to analyze the effects of the laser power, spot diameter, scanning speed, and scanning energy density on the cleaning performance. The simulation results show that the average residual thickness of a paint layer decreases with the increase of the laser power and scanning energy density, and the decrease tendency gradually slows down. When the laser power becomes too large, the metal base will be damaged. The average residual thickness of the paint layer increases with the spot diameter and scanning speed. However, reducing the spot diameter and scanning speed is harmful to enhance the cleaning efficiency. According to the relationship between the physical parameters of the paint layer and the scanning energy density, the optimization protocol of laser cleaning parameters has been proposed by considering both the cleaning performance and the cleaning efficiency. The simulation model is also used to analyze the cleaning performance of each scanning of an uneven surface paint layer by the uninterrupted multiple scanning. The study in this paper could be helpful for the design of laser cleaning devices as well as the optimization of laser parameters.