We will introduces the concept and basic principles of laser cleaning technology, and the experimental method to study the effect of laser cleaning machine in stainless steel surface rust removal, the test shows that the laser cleaning technology can quickly remove the oxidation color of stainless steel weld and heat-affected zone, as well as the paint and rust on the surface of stainless steel, and can form a new passivation layer.
Laser cleaning technology basic principle
Laser cleaning machine technology refers to the use of high-energy laser beam irradiation work surface, so that the surface of the dirt, rust or coating occurs instantaneous evaporation or stripping, high-speed effective removal of cleaning object surface adhesion or surface coating, so as to achieve a clean process.
Laser, together with electron beam and ion beam, are collectively known as high-energy beams. The common feature is that the beam carries high energy transmission in space, and by focusing, the irradiation of 104-1015W/cm² power density can be obtained near the focal point, which is the highest intensity heat source. Laser has the characteristics of high brightness, high directionality, high monochromaticity and high coherence, which is incomparable to ordinary light sources. Using the high brightness of the laser, it can produce temperatures of thousands or even tens of thousands of degrees near the focal point after being focused by a lens. The high directionality of the laser makes it effective for long-distance transmission. The extremely high monochromatic nature of the laser and the single wavelength facilitate focusing and wavelength selection. The laser is transmitted from the fiber optic to the focusing lens, where it is focused and reaches the surface of the workpiece to be cleaned from the nozzle bore. Usually use the nozzle, with the help of the laser coaxial small hole nozzle will have a certain pressure of gas blowing to the cleaning area. Gas is provided by the auxiliary gas source, its main role to prevent the lens from being contaminated by spatter and soot, and play a role in cleaning the surface of the workpiece, strengthening the thermal role of the laser and the material.
Object surface contaminants absorb laser energy, or vaporization and volatilization, or instantaneous thermal expansion to overcome the surface of the particle adsorption force, so that the object from the surface, and then achieve the purpose of cleaning. At present, there is some disagreement on the mechanism of laser cleaning, but most of the mechanism can be a reasonable explanation of some of the phenomena in the laser cleaning experiments, in summary, roughly including laser vapor decomposition, laser stripping, thermal expansion of dirt particles, substrate surface vibration and particle vibration four aspects; and, laser cleaning is often the result of the simultaneous action of a variety of mechanisms.
Laser cleaning mechanism according to the surface adhesion and substrate thermophysical parameters differ in size. When the surface adhesion and the substrate material thermophysical parameters are different, laser cleaning mechanism includes: ablation vaporization, thermal vibration and thermal shock mechanism and acoustic vibration mechanism, such as laser cleaning paint and rubber layer. When the surface adhesion and the substrate material thermophysical parameters do not differ, mainly ablation vaporization mechanism in action, such as laser rust removal.
Stainless steel materials in welding, local parts due to the assembly gap is super poor, resulting in large heat input, especially when using about 3mm thin plate, will lead to surface oxidation near the stainless steel weld and the back of the weld, destroying the original passivation layer of the material, so that the material corrosion resistance is reduced or even failure, the stainless steel exterior of some products do not require painting or painting transparent color varnish, excessive oxidation caused by The color difference will seriously affect the overall beauty of the vehicle. Stainless steel weld over-oxidation mainly occurs on the exterior surface of the vehicle body, such as side walls, lower side wall panels and other parts, especially the side walls and end wall panels (end wall crossband) connection parts, according to the treated surface state differences in light absorption rate, by adjusting the wavelength and other parameters, the laser can not only clean the metal surface oxide layer, but also quickly clean the stainless steel surface rust and paint.
Laser surface cleaning technology can quickly remove stainless steel weld and heat-affected zone oxidation color as well as stainless steel surface paint and rust; laser surface cleaning technology can form a new passivation layer with good corrosion resistance; laser cleaning of the stainless steel surface and the original surface without large color differences.