With the continuous development of high-end fields such as aerospace, petrochemical, high-speed rail, weapons, and nuclear power in China, the environments in which various equipment components are located have also changed accordingly, with increasingly high requirements for the performance of metal material components. To improve overall equipment performance 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, high-pressure water jet cleaning, and chemical cleaning. However, these methods have disadvantages such as low work efficiency, harsh environments, easy damage to the workpiece surface, and inability to meet high cleanliness and high precision cleaning requirements. They also have corresponding technical difficulties and can cause health damage to workers to some extent. Therefore, we need to explore more efficient cleaning methods that do not damage metal materials to more effectively replace traditional cleaning methods.Laser cleaning technology has advantages over traditional methods, such as no need for consumables or auxiliary materials, no damage to metal utensils, easy collection of removed solid powder, and no pollution to the environment. This paper will briefly analyze the basic principles of laser cleaning solutions and elaborate on the applications of laser cleaning technology in metal molds, ship blocks, aircraft metal skins, and other common areas of life.
1. Principles and Characteristics of Laser Cleaning Technology
The essence of laser cleaning technology is to remove different materials, dirt particles, and film layers from solid surfaces. Laser cleaning technology is a surface treatment technology that uses a laser beam with a specific spot shape formed by optical system focusing and spot shaping to irradiate the contaminated area that needs to be cleaned, removing attachments on the substrate surface through vibration, melting, combustion, and even vaporization. Laser Cleaning PrincipleThe entire cleaning process involves the laser scanning regularly and at high speed on the surface of the substrate with pollutants. The pollutants reach the melting or vaporization point and directly burn, vaporize, and decompose to leave the substrate surface. When the laser acts on the substrate surface, most of it is reflected, basically causing no damage to the substrate, thus achieving pollution-free and damage-free cleaning effects. The essence of the entire laser cleaning process is the chemical action between the laser and the contamination layer. According to research, the binding forces between pollutants and the surface they adhere to are mainly covalent bonds, dipole-dipole interactions, etc. Laser cleaning overcomes the interaction forces between pollutants and the substrate surface through continuous laser irradiation, thereby achieving the purpose of laser cleaning. Common laser cleaning methods include:
- Laser dry cleaning: Directly irradiating the substrate surface without using auxiliary methods, mainly suitable for common paint removal, rust removal, and metal surface treatment in industrial production.
- Laser wet cleaning: First covering the substrate surface with a layer of liquid medium, then using laser radiation for decontamination, mainly suitable for cultural relic restoration.
- Inert gas method: Releasing inert gas to the substrate surface while using the laser dry cleaning method to avoid secondary contamination of the cleaned surface, mainly suitable for cleaning aerospace and precision mechanical materials.
- Non-corrosive chemical method: First using laser radiation on the substrate surface to partially detach pollutants, then using non-corrosive chemical agents to remove pollutants, mainly suitable for cleaning stone materials.
In summary, laser cleaning technology is a new “green and environmentally friendly” technology different from chemical cleaning agents or other traditional cleaning processes. It can effectively clean micro or sub-micron level particulate contaminants and has advantages such as stability, high cleaning efficiency, and high degree of automation.
2. Common Application Progress
Understanding the basic principles of laser cleaning technology allows for its application in different scenarios based on its various characteristics. This paper will briefly introduce some of these applications by citing specific experiments.
2.1 Metal Molds
Metal molds are common in daily life. During actual use, factors such as temperature, humidity, sunlight exposure, and pressure in the usage environment may cause microscopic interference and reactions between metal molds and other items, which may lead to damage to metal molds. Therefore, regular maintenance is required. Due to the high cost of manual maintenance, easy damage to the workpiece surface, and high requirements for operator skill level, laser cleaning technology’s high cleaning efficiency and environmental friendliness can meet the needs of this field.Here is an example of laser cleaning of surface contaminants on 316L stainless steel. 316L Stainless Steel Surface Contaminants316L stainless steel has high strength, good plasticity and toughness, and excellent corrosion resistance, so it is widely used in internal structural components of nuclear power plants. Traditional cleaning methods include physical methods and chemical methods. Among them, physical methods mainly include ultrasonic method and high-pressure water jet method; chemical decontamination by cyclic immersion is more common in China’s nuclear power plants, but it has low decontamination efficiency, severe corrosion damage to the substrate, and easily produces secondary waste liquid, greatly affecting the decontamination effect.According to research design orthogonal experiments, reasonable orthogonal test design for various influencing parameters can simplify the complex parameter optimization process. Determine appropriate cleaning gradient thresholds to optimize process tests, complete preliminary preparation work, adjust different laser parameters, test the cleaning effect of lasers on contaminants, and compare whether there are changes in various aspects of metal mold performance before and after cleaning.According to related experiments, laser cleaning technology for cleaning 316L stainless steel samples can not only fully exert its decontamination value but also will not significantly affect the surface characteristics and structure of the test samples. The experimental results show that laser cleaning has a good cleaning effect on 316L stainless steel and can reduce the energy consumption of related facilities. The application of laser cleaning technology in this aspect can effectively slow down the surface corrosion rate of 316L stainless steel in various working environments, which has certain positive significance for the production and use of 316L stainless steel.
2.2 Ship Plates
Ships sailing in the marine environment for long periods suffer from severe rusting of hull plates due to the corrosiveness of seawater. There are also large amounts of marine biological attachments on the hull, which seriously affect the ship’s sailing performance. EH36 steel plates have resistance to marine environment corrosion and are therefore used for ship plates. Currently, 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 generally have high labor intensity and cause serious environmental pollution. Laser cleaning technology has become very mature in some industries and is widely used in many fields. There has also been research on ship plate cleaning. Based on possible contaminants inside the ship’s cabin, the surface is treated with corrosion and rusting, manual painting, and oil smearing to simulate the state of the ship plate to be cleaned, and then laser cleaning technology is used for paint and rust removal. Comparing before and after laser cleaning, laser cleaning has a significant effect. Laser Cleaning Before and AfterHowever, after laser cleaning the surface, it is still necessary to study whether the change in surface state affects the performance of the ship plate substrate. Therefore, the mechanical properties of the samples before and after cleaning are tested. After analyzing the mechanical properties of the samples before and after cleaning, the cleaning process can slightly improve the surface hardness and mechanical properties, and the degree of hardness improvement is affected by process parameters. Therefore, it can be considered that laser cleaning is a non-destructive process and will only slightly increase the surface hardness. The experiment shows that laser cleaning is indeed a more environmentally friendly and pollution-free cleaning method compared to traditional methods. However, the current efficiency of laser paint removal is relatively low, cleaning only about 0.1 square meters per hour, far lower than the efficiency of traditional sandblasting paint removal. Therefore, developing performance evaluation methods for marine equipment after laser paint removal and forming quality evaluation standards are also important supports for the industrialization and application of laser paint removal technology.
2.3 Aircraft Skin
During high-speed flight of aircraft, the paint coating on the aircraft skin surface is prone to aging, damage, peeling, and other phenomena, which greatly reduces the anti-corrosion effect and protective function of the paint coating. Therefore, cleaning and washing the surface skin of aerospace materials is a basic guarantee for the normal operation of aerospace vehicles. Traditional paint removal methods generally have disadvantages such as low efficiency, high energy consumption, insufficient precision in paint layer removal thickness, and poor surface uniformity, which cannot meet the requirements for controllable removal of aircraft skin paint layers. Laser cleaning is a new type of surface cleaning technology that has gradually begun to be applied to aerospace material surface cleaning. Due to its excellent mechanical properties, titanium alloy has been widely used in modern industry, especially in the aerospace field. However, as titanium alloy is a typical difficult-to-process and difficult-to-clean material, traditional cleaning solutions can hardly meet the requirements of the aviation industry for part processing precision, quality, and processing efficiency. Laser cleaning has outstanding advantages in safety, economy, cleaning efficiency, and substrate damage. Moreover, laser spatial positioning is accurate and suitable for complex shapes of aircraft skin and structural parts. Therefore, laser cleaning is considered to be the most promising solution for surface cleaning in the aerospace materials field in the future.According to research, Wen et al. studied the cleaning process of surface coatings on Ti-6Al-4V titanium alloy using pulsed lasers. The test results show that laser cleaning of aircraft skin has different effects at different densities. Laser Cleaning Effects on Aircraft SkinHowever, from the overall cleaning effect. The mechanism of laser cleaning titanium alloy is mainly ablation, accompanied by expansion and vibration effects. The results show that laser cleaning removes surface contaminants through photochemical and photothermal ablation. When the surface of titanium alloy is cleaned, it will slightly remelt and produce shallow pits, which is very beneficial for subsequent coating or welding treatment.Cross-sectional Microstructure of Cleaned Titanium AlloyIn summary, laser cleaning technology has great advantages on aircraft skin. With the improvement of laser technology to meet the high-precision and high-stability cleaning requirements of the aerospace field, efficient and non-destructive cleaning effects can be achieved. With the continuous upgrading of laser cleaning system equipment, improvement of process technology, and assistance of related technologies such as precision positioning, automatic control, and real-time detection in the future, this intelligent cleaning process without consumables and pollution will be more widely applied in the aerospace field.
2.4 Other Fields
Based on the advantages of precise positioning, efficient removal, and wide applicability of substrate materials, laser cleaning technology has application value not only in the above scenarios but also in other aspects of life. Here is a brief introduction to the application of laser cleaning technology in other fields.
- Cultural relic cleaning field: During the entire cleaning process, controlling the intensity of laser cleaning to achieve micro-nano cleaning of corresponding cultural relics at different levels. Laser cleaning technology has been widely used in stone cultural relics, metals, 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, promoting the wider application and development of laser cleaning technology in the field of cultural heritage restoration and protection.
- Nuclear, biological, and chemical decontamination field: Using laser cleaning to remove radioactive materials, toxic agents, biological warfare agents, etc. from equipment surfaces to avoid or reduce nuclear, biological and chemical hazards and achieve normal use of equipment and materials. Due to differences in physical and chemical properties of different decontamination objects and different pollutants, relevant parameters of laser decontamination still need further research.
- Rail vehicle welding field: Applying laser cleaning technology to the process of removing oil stains and oxide films before automatic welding to achieve the effect of cleaning while welding, which can eliminate the oil removal and polishing process before profile assembly and improve assembly efficiency. However, due to related technical reasons, it is still in the initial stage.
3. Conclusion
Laser cleaning technology is a new technology that uses high-energy-density laser irradiation on the substrate surface contamination layer to achieve concentrated heat accumulation, rapidly heating the contamination layer and oxide layer, causing chemical and physical reactions, and achieving separation of contaminants, impurity particles, and oxide layers from the metal surface. With in-depth research, the application of laser cleaning technology will become more and more widespread.
