In the mid-1980s, Beklemyshev, Allrn and other scientists combined laser technology and cleaning technology for practical work needs and conducted related research. Since then, the technical concept of laser cleaning (Laser Cleanning) was born. It is well known that the relationship between pollutants and substrates The binding force is divided into covalent bond, double dipole, capillary action and van der Waals force. If this force can be overcome or destroyed, the effect of decontamination will be achieved. Laser cleaning is the use of laser beams that have the characteristics of large energy density, controllable direction and strong convergence ability, so that the bonding force between the pollutants and the substrate is destroyed or the pollutants are directly vaporized to decontaminate and reduce pollutants. The bonding strength with the matrix, and then achieve the effect of cleaning the surface of the workpiece. When the contaminants on the surface of the workpiece absorb the energy of the laser, they quickly vaporize or instantly expand after being heated to overcome the force between the contaminants and the surface of the substrate. Due to the increased heating energy, the contaminant particles vibrate and fall off the surface of the substrate. The entire laser cleaning process is roughly divided into 4 stages, namely laser vaporization and decomposition, laser stripping, thermal expansion of pollutant particles, substrate surface vibration and pollutant separation. Of course, when applying laser cleaning technology, you should also pay attention to the laser cleaning threshold of the object to be cleaned, and select the appropriate laser wavelength to achieve the best cleaning effect. Laser cleaning can change the grain structure and orientation of the substrate surface without damaging the surface of the substrate, and can also control the surface roughness of the substrate, thereby enhancing the overall performance of the substrate surface. The cleaning effect is mainly affected by factors such as the characteristics of the beam, the physical parameters of the substrate and the dirt material, and the ability of the dirt to absorb the energy of the beam. At present, laser cleaning technology includes three cleaning methods: dry laser cleaning technology, wet laser cleaning technology and laser plasma shock wave technology. 1. Dry laser cleaning means that the pulsed laser is directly irradiated to clean the workpiece, so that the substrate or surface contaminants absorb energy and the temperature rises, resulting in thermal expansion or thermal vibration of the substrate, thereby separating the two. This method can be roughly divided into two situations: one is that the surface contaminants absorb the laser to expand; the other is that the substrate absorbs the laser to generate thermal vibration. 2. Wet laser cleaning is to pre-coat a liquid film on the surface before irradiating the workpiece with a pulsed laser. Under the action of the laser, the temperature of the liquid film rises rapidly and vaporizes. A shock wave is generated at the moment of vaporization, which acts on pollutant particles. , Make it fall off from the substrate. This method requires that the substrate and the liquid film can not react, so the scope of application materials is limited. 3. The laser plasma shock wave is a spherical plasma shock wave generated by breaking down the air medium during the laser irradiation process. The shock wave acts on the surface of the substrate to be washed and releases energy to remove pollutants; the laser does not act on the substrate, so it does not cause damage to the substrate . Laser plasma shock wave cleaning technology can now clean particle contaminants with a particle size of tens of nanometers, and there is no limit to the laser wavelength. In actual production, different test methods and related parameters should be specifically selected according to needs to obtain high-quality cleaning workpieces. In the laser cleaning process, the surface cleaning efficiency and quality evaluation are important metrics to determine the quality of laser cleaning technology.
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