A century after Professor Theodore Harold Maiman invented the world's first ruby laser, lasers that can be used in various fields have appeared one after another. The application of laser technology has led to the rapid development of science and technology in the fields of medical, equipment manufacturing, precision measurement and remanufacturing engineering, and has accelerated the pace of social progress.
In the 1980s, laser beams were irradiated on the contaminated parts of some items, and the irradiated substances underwent a series of physical and chemical processes such as vibration, melting, evaporation and combustion. The pollutants on the surface eventually detached from the surface of the items, achieving the removal of pollutants. Since then, people have begun to study laser cleaning. After decades of development, laser cleaning technology has moved from laboratory research to manufacturing applications, and various laser cleaning machines have gradually entered the ranks of modern intelligent manufacturing equipment.
1. Comparison of laser cleaning and traditional cleaning methods
Laser cleaning technology refers to the use of high-frequency and high-energy laser pulses to irradiate the surface of the workpiece. The coating layer and the contamination layer can instantly absorb the focused laser energy, causing the oil, rust or coating on the surface to evaporate or peel off instantly, and quickly and effectively remove surface attachments or surface coatings. Laser pulses with very short action time will not damage the metal substrate under appropriate parameters. Figure 1 shows the microscopic phenomena of laser cleaning under different mechanisms of gasification processing and micro-impact fragmentation.
Compared with traditional cleaning methods, laser cleaning has some advantages that traditional cleaning methods cannot achieve. Laser cleaning is a non-contact cleaning method that causes little damage to the substrate. It has high flexibility, stability and automation characteristics, good cleaning quality, high precision, and environmental protection. It is a "green" automated cleaning equipment. Table 1 compares different cleaning methods.
2. Composition of laser cleaning system
Although the cleaning equipment is different, the main components are basically similar, including computer control system, laser system, beam adjustment system, etc., see Figure 2. In addition, some supporting equipment is also included: such as dust removal and purification system, manipulator, laser induced breakdown spectrometer (LIBS), visual positioning system and thermal imaging system.
During cleaning, the computer system plays a core communication role, which controls the laser and the optical path adjustment system at the same time. The laser beam is transmitted by optical fiber and enters the beam adjustment system. After the beam is focused, the spot diameter reaches a very small size and acts regularly on the surface of the metal cleaning workpiece.
3. Wide application of laser cleaning technology
Laser cleaning is used as a cleaning process in industrial production, which can effectively remove rust, dirt, paint, carbon deposits, and various coatings. It has been widely used in various fields such as aerospace, rail vehicles, microelectronics, cultural relics protection and medical treatment, as shown in Figure
4.Pre-welding and post-welding cleaning
Laser cleaning technology can be widely used in pre-welding and post-welding cleaning of metal materials such as aluminum alloys, titanium alloys, stainless steel, and high-temperature alloys, which can effectively prevent the generation of defects such as inclusions and pores. After welding, it can also be used for post-welding oxidation cleaning, so that the oxide layer generated during the welding process can be removed again to restore the metallic luster.
The laser cleaning technology was used to locally clean the anodic oxide film of aluminum alloy, and the cleaned welding test plate was butt welded. The weld quality was evaluated by X-ray detection, and the metallographic structure was observed and analyzed. The effect of removing the oxide film on the weld performance was tested by a room temperature tensile test. As shown in Figure 4, the results show that the anodic oxide film was thoroughly cleaned, the tensile strength of the aluminum alloy joint cleaned by laser was 298~303 MPa, and the tensile elongation at break was 6.2%~6.5%. The performance range of the laser-cleaned weld was consistent with that of the mechanically scraped weld. Th
