With the continuous development of high-end fields such as aerospace, petrochemicals, high-speed rail, weapons, and nuclear power, the environment in which each equipment component is located has also changed accordingly, and there are increasingly higher requirements for the performance of metal material components. In order to improve the overall performance of equipment and extend the service life of parts, laser cleaning technology has received widespread attention and research without changing the base material. Common industrial cleaning methods include mechanical grinding cleaning, high-pressure water jet cleaning, chemical cleaning, etc., but these methods have low work efficiency, harsh environment, easy to damage the surface of the workpiece, and cannot meet the high cleanliness and high-precision cleaning requirements. They also have corresponding technical difficulties and cause health damage to workers to a certain extent. Therefore, we need to explore cleaning methods that are more efficient and do not damage metal materials to more effectively replace traditional cleaning methods. Compared with traditional methods, laser cleaning technology has the advantages of not requiring consumables and auxiliary materials, not damaging metal utensils, and the removed solid powder is easy to collect and has no pollution to the environment.

Principles and characteristics of laser cleaning technology

The essence of laser cleaning technology is to remove different materials, dirt particles and film layers on the solid surface. Laser cleaning technology is a surface treatment that uses a laser beam with a specific spot shape formed by focusing and shaping the spot through an optical system to irradiate the contaminated material position to be cleaned, and remove the surface attachments of the substrate by vibration, melting, burning, or even gasification.

The entire cleaning process is that the laser regularly scans the surface of the substrate with dirt on the surface at high speed. The dirt reaches the melting or vaporization point and directly burns, vaporizes and decomposes and leaves the surface of the substrate. When the laser acts on the surface of the substrate, most of it is reflected and basically does not cause damage to the substrate, thus achieving a pollution-free and damage-free cleaning effect. The essence of the entire laser cleaning is the chemical reaction between the laser and the contamination layer. According to research, the binding force between the contaminant and the surface of the object to which it is attached is mainly covalent bond, double dipole and other combinations. Laser cleaning is to overcome the force between the contaminant and the substrate surface through continuous laser, so as to achieve the purpose of laser cleaning. Common laser cleaning methods are: (1) Laser dry cleaning method. That is, without using auxiliary methods, the laser is directly radiated to the substrate surface. It is mainly suitable for common paint removal and rust removal and metal surface treatment in industrial production. (2) Laser wet cleaning method. That is, first cover the substrate surface with a layer of liquid medium, and then use laser radiation to remove contaminants. It is mainly suitable for the restoration of cultural relics. (3) Inert gas method. When using the laser dry cleaning method, inert gas is released to the substrate surface to prevent the cleaned surface from being contaminated again. It is mainly suitable for cleaning aviation, aerospace and precision machinery materials. (4) Non-corrosive chemical method. First, the substrate surface is irradiated with laser to semi-detach the dirt, and then non-corrosive chemical agents are used to remove the dirt. It is mainly suitable for cleaning stone materials. In short, laser cleaning technology is a “green and environmentally friendly” new technology that is different from chemical cleaning fluids or other traditional cleaning processes. It can effectively clean micron or submicron-level particulate dirt and has the advantages of stability, high cleaning efficiency, and high degree of automation.

Metal molds

Metal molds are very common in life. In actual use, the temperature, humidity, sunlight, pressure, etc. of the use environment may cause microscopic interference and reaction between metal molds and other objects. These factors may cause damage to metal molds, so they need to be maintained regularly. Due to the high cost of manual maintenance, it is easy to cause damage to the surface of the workpiece, and it has high requirements on the operating level of the staff. Therefore, laser cleaning technology has high cleaning efficiency and no pollution to the environment, which can meet the needs of this field.

316L stainless steel has high strength, good plasticity and toughness, and excellent corrosion resistance, so it is widely used in the internal structural parts of nuclear power plants. Traditional cleaning methods are physical and chemical methods. Among them, the physical method mainly includes ultrasonic method and high-pressure water jet method; among chemical decontamination, the cyclic immersion method is more commonly used in nuclear power plants in my country, but the decontamination efficiency is low, the corrosion damage to the substrate is serious, and it is easy to produce secondary waste liquid, which greatly affects the decontamination effect.

Ship plates

Ships sail in the marine environment for a long time. Due to the corrosiveness of seawater, the hull plates will be seriously corroded. There are also a large number of marine biological attachments on the hull, which will seriously affect the navigation performance of the ship. EH36 steel plates are resistant to marine environmental corrosion, so they are used in ship plates. At present, the traditional cleaning methods for ship paint and rust removal mainly include: mechanical grinding, sandblasting, high-pressure water jet, chemical cleaning, etc. Although traditional cleaning methods basically meet the needs of hull cleaning, they are generally labor-intensive and cause serious pollution to the environment. Laser cleaning technology in some industries is very mature and widely used in many industries. There are also studies on ship plate cleaning. Based on the pollutants that may exist in the cabin, the surface is corroded and rusted, painted manually, and smeared with oil to simulate the state of the ship plate to be cleaned, and then the laser cleaning technology is used to remove paint and rust.

Aircraft skin

During the high-speed flight of an aircraft, the paint coating on the surface of the aircraft skin is prone to aging, damage, and shedding, which greatly reduces the anti-corrosion effect and protective effect of the paint coating. Therefore, cleaning the surface skin of aerospace materials is the basic guarantee for the normal operation of aerospace vehicles. However, traditional paint removal methods generally have disadvantages such as low efficiency, high energy consumption, insufficient precision of paint layer removal thickness, and poor surface uniformity, which cannot meet the controllable removal requirements of aircraft skin paint layers. Laser cleaning is a new type of surface cleaning technology that has gradually begun to be used in the surface cleaning of aerospace materials. Due to its excellent mechanical properties, titanium alloys have been widely used in modern industry, especially in the aviation field. However, since titanium alloys are typical difficult-to-process and difficult-to-clean materials, traditional cleaning solutions are difficult to meet the requirements of the aviation industry for parts processing accuracy, quality and processing efficiency. Laser cleaning has outstanding advantages in safety, economy, cleaning efficiency, substrate damage, etc., and the laser has accurate spatial and temporal positioning, which is suitable for complex-shaped fuselages and structural parts on aircraft skins. Therefore, laser cleaning is considered to be the most promising solution in the field of surface cleaning of aerospace materials in the future.

Other fields

According to the advantages of laser cleaning technology such as precise positioning, efficient removal, and wide application of substrates, its application value is not only in the above-mentioned scenarios, but also in other aspects of life. Here is a brief introduction to the application of laser cleaning technology in other fields.
(1) Cultural relics cleaning field. During the entire cleaning process, the intensity of laser cleaning is controlled to achieve micro-nano cleaning of the corresponding cultural relics layer by layer. Laser cleaning technology has been widely used in stone cultural relics, metal, murals and other cultural relics. With the continuous development of laser technology, there will be more suitable laser systems and more optimized cleaning parameters for different types of cultural relics, which will promote the wider application and development of laser cleaning technology in the field of cultural heritage restoration and protection.
(2) Nuclear, biological and chemical decontamination field. Laser cleaning light removes radioactive substances, toxic agents, biological warfare agents, etc. on the surface of equipment to avoid or reduce nuclear, biological and chemical hazards and realize the normal use of equipment and materials. Due to the differences in the physical and chemical properties of different decontamination objects and different pollutants, the relevant parameters of laser decontamination need further research.
(3) Rail vehicle welding field. Laser cleaning technology is applied to the process of removing oil and oxide film before automatic welding, achieving the effect of cleaning and welding at the same time, which can save the degreasing and grinding process before profile assembly and improve assembly efficiency. However, due to relevant technical reasons, it is still in its infancy.

Conclusion

Laser cleaning technology is an emerging technology that uses high-energy-density lasers to irradiate the contamination layer on the surface of the substrate, achieve heat concentration, quickly heat the contamination layer and the oxide layer, and form chemical and physical reactions to remove contaminants such as the contamination layer, impurity particles, and the oxide layer from the metal surface. With the deepening of research, the application of laser cleaning technology will become more and more extensive.