Since the first laser was invented in 1960, lasers have been widely used in various fields. In the industrial sector, lasers are mainly used for cutting, drilling, and welding in industrial production applications.
In recent years, with the breakthrough of fiber laser technology and the increasingly stringent environmental protection requirements in China, traditional industrial cleaning techniques are facing serious challenges. Finding a cleaner and non-damaging cleaning method is a problem that we must consider.
Laser cleaning, as a revolutionary technology, has the characteristics of high efficiency, convenience, environmental friendliness, non-grinding, non-contact, no thermal effects, and applicability to cleaning objects of various materials.
It can replace traditional chemical and mechanical cleaning methods and has great potential in various fields of daily production and life.
Laser cleaning is a non-contact dry cleaning method that has advantages that traditional cleaning methods do not have, especially in high-demand cleaning areas such as PCB board post-processing, cleaning of magnetic media surfaces, removal of laser etching and sputtering particles, cleaning of cultural relics surfaces, and cleaning of various precision instruments.
In these applications, laser cleaning has unparalleled advantages. Automated cleaning equipment equipped with process monitoring functions will be widely used in the field of precision cleaning.
Cleaning Principle
Figure 1 shows a schematic diagram of the principle of laser peeling off surface attachments. Laser cleaning mostly uses high-energy pulse lasers for cleaning, which have ultra-high energy density.
During the interaction between light and matter, the surface attachment is detached from the object surface and absorbed by the system, effectively removing the attachment on the substrate surface without affecting the surrounding environment.
A prominent advantage of laser cleaning is that the substrate is not damaged during the removal of surface attachments.
In order to achieve this non-destructive testing, various parameters in the cleaning process need to be adjusted to ensure that the energy density of the interaction with matter is less than the damage threshold of the substrate.
Through experimental research and theoretical analysis, it is generally believed that there are two mechanisms for removing attachments in laser cleaning: instantaneous vaporization of attachments and detachment of attachments from the substrate surface due to laser shock.
Current Application Status
Research on laser cleaning technology began in the mid-1980s. However, it was not until the early 1990s that it was truly introduced into industrial production and gradually replaced traditional cleaning methods in many occasions.
Abroad, laser cleaning has a very wide range of applications, from thick rust layers to surface fine particles, which can be removed with lasers. Many types of equipment are used in laser cleaning experiments, and the wavelength range of the laser used is quite wide.
The development of laser cleaning technology is not balanced, some have achieved industrialization, and some are still in the laboratory stage. With the development of industrial robots and the combination of laser and robot technology, laser cleaning systems have great application prospects in various industries.
Currently, laser cleaning equipment can play an important role in the fields of automobile manufacturing, semiconductor wafer cleaning, military equipment cleaning, building exterior wall cleaning, cultural relic protection, circuit board cleaning, LCD screen cleaning, gum residue removal, etc. in the domestic market.
According to statistics, there are nearly 4,000 companies in China engaged in laser-related businesses, while the number of companies engaged in laser cleaning product development is less than 1%. For a market with huge demand, this number cannot meet the actual demand.
The reasons for this situation are mainly as follows:
(1) The unit price of the equipment is relatively high. For products with low added value in cleaning, the initial investment in equipment is too large, which leads to a lower acceptance of laser cleaning equipment by enterprises;
(2) The cleaning efficiency and effect need to be improved;
(3) It is necessary to effectively cater to process value measurement technology to ensure the safety of cleaning.
Technological breakthroughs
Currently, most of the laser cleaning equipment on the market is aimed at researching and developing related products for cleaning organic pollutants, oxides, surface coatings, and other attachments on the substrate surface.
It is necessary to develop efficient, low-power, and multi-mode precision laser cleaning equipment with targeted functions, especially for the development of optical modules that need to meet the functional needs of various industries. Figure 2 shows a schematic diagram of using oblique incidence pulse cleaning.
The experiment shows that when cleaning stains on marble surfaces and oxide films on copper surfaces, the cleaning efficiency can be increased by 5-10 times compared with vertical incidence by using a certain beam incident angle.
By developing suitable optical modules, the cleaning efficiency can be improved without increasing the laser power. With this technology, equipment costs can be reduced while maintaining the same cleaning efficiency.
Figure 3 shows a schematic diagram of laser shock wave cleaning. When cleaning small particles on the surface of precision instruments, since the particle size of the attachments is small and there are mainly three types of binding forces between the attachments and the substrate, namely van der Waals force, capillary force, and electrostatic force.
Due to the small size of these pollutants, it is difficult to clean them using traditional methods. Direct plasma treatment through high-energy pulses can easily damage the substrate material.
In this case, laser shock wave cleaning can be used. By finely controlling it, the air is broken through at a certain distance above the object being cleaned, forming an impact liquid, which destroys the binding force between the contaminant particles and the substrate. The particles are then collected by negative pressure meters, achieving non-destructive cleaning.
In addition, real-time monitoring of the cleaning process is also a hotspot and difficulty in the development of laser cleaning equipment.
Currently, commonly used real-time monitoring technologies mainly include laser-induced breakdown spectroscopy technology, acoustic wave technology, image recognition technology, and speckle interferometry measurement technology.
Among these technologies, spectral technology is not integrated due to its high cost and sensitivity to environmental factors. Acoustic wave technology is also limited by its sensitivity to surrounding noise, limiting its integration feasibility.
Image recognition technology has strong randomness in determining evaluation thresholds, making it difficult to quantify and requiring further research on its feasibility. Speckle technology can characterize surface roughness in real-time.
As long as a quantitative relationship between roughness and cleanliness is established, this technology can have the potential for real-time monitoring of cleaning.
Conclusion
The promotion and popularization of laser cleaning technology is based on the premise of technical safety and feasibility, and conforms to the national advocacy of green manufacturing. Suzhou Deveir Optoelectronic Technology Co., Ltd. has made certain breakthroughs in laser cleaning technology and real-time monitoring technology, and has delivered the world’s first nuclear industry cleaning workstation to customers, as shown in Figure 4.
The future development direction of laser cleaning equipment is to meet the flexible and efficient cleaning needs of customers while ensuring safe cleaning.
