Laser cleaning technology refers to the process of using a high-energy laser beam to illuminate the surface of the workpiece, causing the dirt, rust or coating on the surface to evaporate or peel off instantly, thereby achieving cleanliness.
1. Classification and characteristics of laser cleaning technology
There are generally four methods of laser cleaning：
(1) Laser dry cleaning method, that is, the use of pulsed laser direct radiation decontamination.
(2) The laser + liquid film method, that is, a layer of liquid film is first deposited on the surface of the substrate, and then the liquid film is exploded and decontaminated with a laser.
(3) The method of laser + inert gas, that is, while the laser is radiating, an inert gas is used to blow to the surface of the workpiece. When the dirt is peeled off from the surface, the gas is blown far away from the surface to avoid re-pollution and oxidation of the clean surface.;
(4) After loosening the dirt with a laser, decontaminate it by non-corrosive chemical methods.
At present, the first three cleaning methods are mainly used in industrial production. Among them, the laser dry cleaning method is used to take the laser + liquid film cleaning method. More，the fourth method is only seen in the cleaning and protection of works of art.
2. Compared with the traditional cleaning process, the characteristics of laser cleaning technology：
(1) It is a kind of "dry" cleaning, does not require cleaning liquid or other chemical solutions, and the cleanliness is much higher than the chemical cleaning process.
(2) The scope of dirt removal and the applicable substrate range are very wide.
(3) By regulating the laser process parameters, pollutants can be effectively removed without damaging the surface of the substrate, so that the surface is as old as new.
(4) Laser cleaning can be easily automated.
(5) Laser decontamination equipment can be used for a long time and has low operating costs.
(6) Laser cleaning technology is a “green” cleaning process. The waste eliminated is solid powder, small in size, easy to store, and basically does not pollute the environment.
3.Mechanism of laser cleaning:
The laser cleaning mechanism is mainly based on the absorption of laser energy by pollutants on the surface of the object, or vaporization and volatilization, or instantaneous thermal expansion to overcome the adsorption force of the surface on the particles, so that they leave the surface of the object, and then achieve the purpose of cleaning. At present, there are some differences in the mechanism of laser cleaning, but most of the mechanisms can reasonably explain some of the phenomena in the laser cleaning experiment. In summary, it roughly includes laser vaporization and decomposition, laser stripping, thermal expansion of dirt particles, surface vibration of the substrate, and particle-to-particle vibration. Four aspects, and laser cleaning is often the result of multiple mechanisms acting at the same time.
Based on the analysis of a large number of experimental results, it is believed that the laser cleaning mechanism varies according to the size of the difference between the thermophysical parameters of the surface attachment and the substrate. When the thermophysical parameters of the surface attachment and the base material are very different, the laser cleaning mechanism includes: Ablation and vaporization, thermal vibration and thermal shock mechanism and acoustic wave vibration mechanism, such as laser cleaning of paint and rubber layers. When the thermophysical parameters of the surface attachment and the base material are not much different, the ablation and vaporization mechanism is mainly at work, such as laser rust removal. This principle is the principle.