Laser cleaning is an important laser application and is known as the “most promising green cleaning technology of the 21st century.” It has unique advantages that make it effective in the efficient and precision cleaning of large and complex components. This technology can be used to clean parts that cannot be cleaned using traditional technology, significantly improving the cleaning efficiency and reliability of the product. Although developed countries abroad have performed much work on the basic theory, process exploration, and engineering application of laser cleaning, there are still common problems such as a low component cleaning efficiency, an unclear coupling mechanism, incomplete evaluation standards, and insufficient online monitoring technology. Therefore, researching the basic theory and equipment for efficient laser cleaning is a specific implementation goal of the “Made in China 2025” initiative, which aligns with China’s sustainable development strategy. This will assist in improving the automation level of equipment maintenance in areas such as the aerospace, rail transit, and ocean shipping sectors, and has important significance in promoting the upgrading and optimization of China’s industrial structure.

This study focuses on the significant demand for laser cleaning in the aerospace, high-speed rail, and ocean shipping fields in China. It considers large and complex components such as the TA15 titanium alloy intake ports for the new generation of aerospace solid-liquid ramjet engines, high-speed rail body features or bogie components, and hatch covers in oceangoing ship manufacturing as research objects. It introduces the research progress of the Harbin Institute of Technology in laser cleaning mechanisms and processes, the online monitoring of multiple parameters during cleaning processes, and intelligent equipment technology in recent years in order to provide valuable references for the sustainable development of intelligent laser manufacturing in China in the future.To overcome the shortcomings of online monitoring technology for laser cleaning at home and abroad, the team of Guo Bin and Xu Jie from the Harbin Institute of Technology established a coupled multivariate rapid identification method for laser cleaning and its key technologies for short-term online regulation. They established a multi-parameter online detection and regulation system based on spectroscopy (Fig.17), providing technical support for the subsequent development of intelligent, flexible, and selective precision laser cleaning equipment and efficient laser cleaning equipment for large components. This system achieves real-time control of the laser cleaning quality, and the accuracy errors of laser spot size and average power output are better than 1%. The Harbin Institute of Technology has completed the development of a complete set of equipment for large-scale component cleaning in fields that include ocean shipping, high-speed rail, and nuclear power, integrating systems and devices such as lasers, computer numerical control (CNC) systems, industrial robots, cleaning end effectors, water cooling equipment, dust removal equipment, and safety protection devices for the first time in China (Figs.26 and 27). Based on the complete set of laser cleaning equipment for large components, research has been carried out on laser cleaning processes such as rust removal for ship hatch cover features, paint removal for high-speed rail bogie wheelset features, and the removal of marine microorganisms on nuclear power floating bucket features, as well as functional verification of gantry-type CNC laser cleaning equipment. A complete set of process solutions for the laser cleaning of large components in the ocean shipping and high-speed rail fields has been provided, with a cleaning efficiency exceeding 50 m²/h.

Different methods are involved in the binding of objects such as coatings, dirt, marine microorganisms, and small particles to a substrate, and it is necessary to distinguish and research different physical removal mechanisms based on the physical characteristics of various objects. When cleaning the oxide film on the surface of a titanium alloy inlet, nanosecond pulse laser cleaning can not only completely remove the oxide film on the titanium alloy surface but can also prevent secondary oxidation of the substrate as a result of the low thermal effect characteristics of nanosecond laser, making it an optimal laser cleaning method (Fig.3). When cleaning a painted high-speed railway aluminum alloy car body, different colors and thicknesses of paint require different laser cleaning methods (Fig.4). When the paint is thin (≤40 μm), a laser light source with a lower absorption rate for the paint is selected, and the paint is removed through thermal vibration, which achieves better results. When the paint is thick, it is necessary to choose a laser light source with a higher absorption rate for the paint, and the paint is removed using an ablation mechanism, which is a good choice. For the laser cleaning of high-strength steel hull rust, the main removal mechanism during dry cleaning involves energy absorption by the oxide film and gasification (Fig.5). When the oxide on the surface undergoes gasification and evaporation, the downward reaction force is generated on the sample surface, making the removal of the deeper oxide film easier. Laser cleaning using a narrow pulse width and high peak power is effective at removing marine microorganisms (Fig.6). The laser removal mechanisms for the extracellular polymeric substances (EPS) layer and barnacle substrate are ablation gasification and shock wave peeling, respectively. Establishing a cleaning thermal vibration model will assist in better elucidating the change laws of the laser cleaning behavior, temperature field, and stress field with the laser spatiotemporal energy characteristic parameters and predicting the relationship between the different cleaning parameters and cleaning quality in the laser cleaning process. The team of Guo Bin and Xu Jie from the Harbin Institute of Technology established a thermal vibration model using the finite element method to simulate the temperature and stress fields during laser cleaning (Figs.7‒10). The results were compared with experimental results. The final calculation accuracy of the temperature and thermal stress fields exceeded 85%.

Laser cleaning technology can significantly improve equipment manufacturing, protect the environment, and reduce labor requirements. It will bring users direct economic benefits of tens of millions or even billions of yuan. Moreover, innovative core technologies can be promoted by appropriate enterprises, universities, and research institutes, with significant economic and social benefits. The different application fields for laser cleaning lead to a significant demand for laser cleaning equipment. Domestically, much attention is being given to the remanufacturing industry, including a massive demand for engineering machinery, automotive parts, and machine tool remanufacturing. Thus, laser cleaning equipment has broad market prospects. Establishing optimization process specifications for the laser cleaning of typical component surface contaminants, developing a laser multi-parameter online detection system for the laser cleaning process, selecting intelligent and flexible robots for precision laser cleaning equipment, and developing efficient laser cleaning equipment for large components will assist in maintaining China’s leading position in the field of innovative laser manufacturing.