“Cleaning operation is one of the essential key links in industrial production process, which plays an important role in improving product quality and prolonging service life. Under the background of vigorously promoting the transformation and upgrading of the manufacturing industry, the traditional cleaning methods have been unable to meet the application needs of the industrial field, especially in the high-end application field, the advanced laser cleaning technology has been paid more and more attention.”
Laser is a kind of beam with concentrated energy, which is especially suitable for material surface treatment. The first laser came out in the 1960s. In 1969, first proposed the concept of laser cleaning. In the 1980s, IBM used laser cleaning to clean the contaminated part of the mask for electron beam projection amplification. Through the interaction between laser and sub-micron particles on the surface, the impurity particles with strong adhesion (about 106 times of its own gravity) were successfully removed, which perfectly solved the problem that the traditional cleaning method could not remove the micro particles, The economic value of laser cleaning technology is highlighted. Subsequently, a research group led by Petrov from Russia, Zapka from Germany and Allen from the United States further studied the laser cleaning experiment of mask, and the laser cleaning technology gradually developed.
Laser cleaning system is a kind of typical optical, mechanical and electrical integration equipment, involving optical engineering, software engineering, detection technology, mechanical engineering and other disciplines.
As laser is a processing tool, laser cleaning has the typical characteristics of laser processing. Moreover, due to the wave particle duality of laser, there are both thermal and powerful effects in the area of laser acting on materials. Compared with traditional cleaning methods, laser cleaning has unique advantages.
Environmental friendly and pollution-free cleaning.
Compared with the traditional cleaning method, it needs a lot of water, and laser cleaning almost does not consume water resources. No chemical agent is used in the cleaning process. No chemical agent and cleaning solution are needed in laser cleaning. No waste liquid is discharged. Basically, the waste materials are solid materials. Special auxiliary equipment can be used to collect solid residues. The volume is small and easy to store. In the process of laser beam action, no additional impurities will be introduced.
Localized nondestructive high precision cleaning.
The laser has good directive, easy to determine the cleaning area, and centralized implementation of precision removal. Using the different absorption coefficients of the surface pollutants and the substrate to the laser, by setting the pulse energy, spot size and other parameters, the selective removal can be carried out without damage to the substrate. For example, the traditional industrial cleaning method can not effectively remove the particles with size less than 1 μ The laser cleaning technology can realize the high precision cleaning of nano process manufacturing process. Due to the short action time of nanosecond pulse laser, the instantaneous acceleration can reach 109m / s ²， Enough to overcome the adhesion between particles and work-piece surface.
Non contact cleaning.
Compared with the traditional contact cleaning method, laser cleaning can convert the laser light energy into the removal force, without electromagnetic interference, grinding, contact and mechanical damage, so it saves the cost and trouble of tool replacement.
The operation is safe and convenient.
The laser can be operated remotely and can be used for cleaning in dangerous places, such as cleaning the internal pollutants of nuclear facilities. For precision parts with complex surface shape, the surface quality of existing traditional cleaning methods such as manual cleaning, mechanical cleaning or chemical cleaning is not high, or even can not be cleaned. The output mode of laser is various, which can be realized by a variety of optical systems. Combined with the control output mode of optical fiber or manipulator, the pollutant cleaning of complex shape (such as angle steel, cylinder) or difficult to reach position (such as corner) can be realized.
Easy to integrate with welding and other follow-up equipment.
Laser cleaning system is easy to integrate with other equipment, and it is also suitable for automatic production line. It can simplify the process, shorten the manufacturing cycle of products, improve the production efficiency of products, ensure the quality of products, and has high economic value.
Under the same process parameters, the laser cleaning effect is almost the same, with good repeatability, suitable for high demand occasions. At the same time, good repeatability helps to realize the standardization of laser cleaning technology, improve the applicability of laser cleaning products, processes and services, and promote technical cooperation. It can also solve the problems of uneven cleaning effect and large level difference in traditional cleaning operation.
Easy to achieve micro area and large area cleaning.
Laser focusing induces the generation of plasma, and the influence area can reach micron scale, which can realize the micro area cleaning of cracks, scratches, small holes and so on. For large area cleaning, the scanning output laser mode is adopted. Because the laser has good space controllability and time controllability, it can realize large-scale cleaning without area limitation.
As an advanced technology, laser cleaning is regarded as the “subversive” of cleaning industry. The application scope of laser cleaning technology is very wide, and it has great potential in industrial development, almost covering the entire industrial field.
At present, the development of laser cleaning technology is unbalanced, and it has been partially industrialized in high-end manufacturing fields, such as semiconductor, marine equipment, automobile manufacturing, aerospace, high-speed rail transportation, etc. Nowadays, advanced manufacturing industry has become the commanding point of international competition. The development of laser cleaning technology has a very important strategic significance for China’s equipment international competitiveness, economic and social development. This book (article) mainly studies the typical laser cleaning technology and application in high-end manufacturing field.
- Laser cleaning technology was first used in semiconductor industry. With the rapid development of submicron and deep submicron VLSI following the “Moore’s law”, the design line width decreases sharply. The submicron dirt on the surface of the substrate is enough to cause a large number of defects. The pollution particles on the surface of the circuit board have great adsorption force with the substrate Mechanical cleaning and ultrasonic cleaning methods can not effectively remove micron and submicron particles, or cause matrix damage when removing micro particles. Laser cleaning technology came into being under this background. On the basis of overcoming the shortcomings of traditional cleaning technology, it also shows great advantages. Zapka and others applied for the patent of laser cleaning for the first time in 1987. In the 1990s, laser cleaning technology was successfully applied in semiconductor manufacturing process to remove micro particles on mask surface, realizing the application of early laser cleaning technology in semiconductor industry. After that, laser cleaning technology was widely used in semiconductor industry. At present, the relevant technology is relatively mature. Tan Donghui, Lu Dongsheng and others in China use excimer laser to clean silicon wafer directly. According to the temperature distribution of substrate surface in the process of laser cleaning, the cleaning threshold and damage threshold of silicon wafer cleaning are deduced to further improve the process of laser cleaning in semiconductor industry.
- Replacing traditional sand blasting cleaning technology with laser cleaning makes marine equipment industry full of expectations. Although the traditional sand blasting technology is relatively mature, it has some disadvantages, such as excessive hairiness, serious tool loss, environmental pollution, and great damage to the body of workers engaged in sand blasting for a long time. However, other cleaning methods such as pickling and high-pressure water cleaning are seriously polluted, ultrasonic and pneumatic cleaning methods are not thorough, and laser cleaning has no water pollution and dust can be recycled, which is especially suitable for marine environment. Therefore, the development of laser cleaning in ship manufacturing and repair, deep-sea drilling and oil storage platform, port machinery, containers and other aspects of the application, can improve the surface properties of materials and equipment anti wave ability, service safety and life.
- Laser cleaning technology is widely used in automobile manufacturing industry to meet the needs of high quality cleaning. Chihalo company provides optical fiber laser cleaning equipment for Audi TT automobile production line to clean the oxide film on the surface of light aluminum alloy door frame. The research on the removal of Al Si coating on the surface of automobile hot formed steel was carried out in China. Using fiber laser to clean the fast drying thermoplastic acrylic aerosol paint on the surface of automobile aluminum alloy plate substrate, not only achieves the ideal paint removal effect, but also improves the mechanical properties of the substrate surface.
- Laser cleaning is also used in automobile tire mold cleaning. Although the initial investment cost is high, it has great advantages in saving standby time, avoiding mold damage, working safety and saving raw materials. Laser cleaning experiments show that it only takes 2 hours to clean a set of large truck tire mold online, and the cleaning effect is good. Compared with the conventional cleaning method, the economic benefit is obvious.
- The high-speed rail and aerospace fields have high requirements on the surface properties of materials. Using laser to clean the fuselage paint and realize the pre-treatment of composite materials before bonding can solve the problems of low efficiency, uneven removal, poor surface properties and heavy environmental pollution. The composite surfaces of the propeller blades of the US Navy h53 and h56 helicopters and the flat tail of the F16 fighter plane have been used for laser paint removal. Schweizer of Germany successfully used a 2kW CO2 laser to remove the paint from the fuselage of the aircraft.
- For the industrial cleaning of nuclear power plant and other fields, the factor of radioactive materials should be considered. The conventional cleaning method needs the manual control of the operator, and the radioactive materials will cause great harm to the human body. The laser cleaning method can use optical fiber and operating system to realize remote control, and can be applied to the cleaning of dangerous locations such as nuclear facilities. Itoh et al. Used laser to clean the metal sheet polluted by radioactive cesium chloride solution. Hou Suxia et al. Studied the laser cleaning technology of steam generator heat transfer tube in nuclear chemical industry, and the experimental results showed that the surface pollutants were 100% removed. Roberts et al. Used laser cleaning to remove uranium mixture on metal surface. Delaporte et al. Carried out experimental research on laser removal of radioactive oxides on the surface of different metal samples. Aniruddha used laser shock wave method to remove radioactive particles from the surface of glass.
- Precision cleaning of medical devices such as injection needles and surgical tools needs to pass human health inspection, which is a very difficult process. At present, the cleaning and disinfection process is to use water or Freon solution for cleaning, and then use high temperature and high pressure for disinfection and sterilization. There are many intermediate links, which increase the possibility of disease infection. The cleaning and disinfection time is long, and it is easy to produce a lot of sewage. Laser cleaning does not introduce impurities. The high pressure and high temperature generated by laser cleaning can not only quickly remove all kinds of pollutants on medical devices, but also kill all kinds of bacteria and viruses. At the same time, it can achieve the effect of cleaning and disinfection, save cleaning time, and meet the requirements of high-precision cleaning of medical devices. It can replace the current Freon chemical cleaning and improve the accuracy of cleaning Safety and success rate.
- Optical products have high requirements for cleaning equipment. Conventional physical cleaning may cause damage to precise optical elements. Complex and precise optical equipment needs to avoid off-line separation and cleaning of optical elements. As a high-precision cleaning technology, laser cleaning does not cause secondary pollution and damage optical elements. It can be accurately positioned and cleaned through optical fiber or conducting head, Realize the online cleaning of optical elements. Especially for optical elements with fine surface structure (such as gold-plated grating), conventional cleaning technology can not solve the problem of removing micro particles, so laser cleaning technology opens up a new way. Han Fengming used laser to clean the particle pollutants on the surface of K9 glass to achieve fixed-point cleaning, without damage to the K9 glass substrate, and effectively removed the micron level or even submicron level pollutants. Through the analysis of the micro morphology and the influence on the optical aperture, the results show that compared with chemical etching cleaning, laser cleaning has better safety and applicability.
Green, environmental friendly and efficient laser cleaning is a promising industrial cleaning technology, which will gradually replace the traditional cleaning process. There are many problems in laser cleaning technology and equipment due to many cleaning objects, various cleaning conditions and strict cleaning requirements: there is no complete theoretical support, such as the mechanism of surface pollutant removal and the mechanism of substrate surface damage; Lack of detection and monitoring of cleaning process, complex surface cleaning process and automation equipment, etc., affect the cleaning efficiency, surface quality and precision control. Therefore, on the basis of a large number of experiments and theoretical studies, it is of great scientific significance, engineering practical value and potential huge economic benefits to clarify the various mechanisms between the laser and the object being cleaned, analyze the detection and control of multiple parameters in the laser cleaning process, establish the cleaning process database, and realize the effective control of the laser cleaning effect.