For example, when there are sub-micron pollution particles stuck on the surface of the workpiece, these particles are often stuck very tightly, and conventional cleaning methods cannot remove them, but cleaning the surface of the workpiece with nano-laser radiation is very effective. Also, because the laser cleans the workpiece without contact, it is very safe to clean the precision workpiece or its fine parts, and its accuracy can be guaranteed. Therefore, laser cleaning has unique advantages in the cleaning industry.
Why can a laser be used for cleaning? Why does it not cause damage to the object being cleaned? First understand the nature of the laser. To put it simply, the laser is no different from the light (visible light and invisible light) that surrounds us, except that the laser uses a resonant cavity to gather light in the same direction, and has a relatively simple wavelength, coordination, etc. The performance is better, so theoretically all wavelengths of light can be used to form lasers, but in practice, limited by the limited number of media that can be excited, the laser light sources that can produce stable and suitable for industrial production are quite limited. The widely used ones are probably Nd: YAG laser, carbon dioxide laser and excimer laser. Since Nd:YAG laser can be transmitted through optical fiber and is more suitable for industrial applications, it is also widely used in laser cleaning.
Technically speaking: Laser ablation (the scientific name for laser cleaning) or photoablation is the process of removing material from a solid (or sometimes liquid) surface by irradiating it with a laser beam. At low laser fluence, the material is heated by the absorbed laser energy and vaporized or sublimated. At high laser fluences, the material is often converted to a plasma. Typically, laser ablation refers to the removal of material with a pulsed laser, but if the laser intensity is high enough, material can be ablated with a continuous wave laser beam. Excimer lasers with deep ultraviolet light are mainly used for photoablation. The laser wavelength used for photoablation is about 200 nm. The depth to which laser energy is absorbed and the amount of material removed by a single laser pulse depend on the optical properties of the material as well as the laser wavelength and pulse length. The total mass ablated from the target per laser pulse is often referred to as the ablation rate. Laser radiation characteristics such as laser beam scanning speed and scan line coverage can significantly affect the ablation process.
Advantages
Compared with mechanical friction cleaning, chemical corrosion cleaning, liquid solid powerful impact cleaning, high-frequency ultrasonic cleaning and other traditional cleaning methods, laser cleaning has obvious advantages.
laser cleaning is a "green" cleaning method, it does not need to use any chemicals and cleaning solutions, cleaning down the waste is basically a solid powder, small size, easy to store, recyclable, and can easily solve the environmental pollution problems caused by chemical cleaning.
traditional cleaning methods are often contact cleaning, cleaning the surface of the object has a mechanical force, damage to the surface of the object or cleaning media attached to the surface of the object to be cleaned, which can not be removed, resulting in secondary pollution. Laser cleaning is non-abrasive and non-contact, so these problems are solved.
lasers can be transmitted through optical fiber, with robots and robotic arms, easy to achieve long-distance operation, and can clean the parts that are not easy to reach with traditional methods, which can ensure the safety of personnel in some dangerous places.
Laser cleaning can remove various types of contaminants from the surface of various materials to achieve a cleanliness that cannot be achieved by conventional cleaning. And it can also selectively clean the surface of the material pollutants without damaging the surface of the material.
laser cleaning is efficient, saving time.
purchase laser cleaning system, although the initial one-time investment is high, but the cleaning system can be used for a long time stably, with low operating costs, only electricity costs per hour.
Work Principle
The pulsed Nd: YAG laser cleaning process relies on the characteristics of the light pulses generated by the laser, based on the photophysical reaction caused by the interaction between the high intensity beam, the short pulse of laser light, and the contaminated layer. The physical principles can be summarized as follows.
The light beam emitted by the laser is absorbed by the contamination layer on the surface to be treated.
The absorption of large energy forms a rapidly expanding plasma (a highly ionized unstable gas), which generates a shock wave.
The shock wave turns the contaminant into fragments and rejects them.
The light pulse width must be short enough to avoid heat build-up that can damage the treated surface.
Experiments have shown that plasma is generated on metal surfaces when oxides are present on the surface.
Plasma is only generated at energy densities above a threshold value that depends on the contamination or oxide layer being removed. This threshold effect is important for effective cleaning while keeping the substrate material safe. There is also a second threshold value for the appearance of plasma. If the energy density exceeds this threshold, the substrate material will be destroyed. In order to clean effectively while ensuring the safety of the substrate material, the laser parameters must be adjusted to the situation so that the energy density of the light pulse is strictly between the two thresholds.
Each laser pulse removes a certain thickness of the contamination layer. If the contamination layer is thick, multiple pulses are required for cleaning. The number of pulses required to clean the surface depends on the degree of surface contamination. An important result of the two thresholds is the self-control of cleaning. Energy density higher than the first threshold of light pulses will keep rejecting contaminants until they reach the substrate material. However, because its energy density is below the threshold of damage to the substrate material, the substrate will not be damaged.
Application
Laser cleaning can be used not only to clean organic contaminants but also to clean inorganic materials, including metal rust, metal particles, dust, etc.. Here are some practical applications, these technologies have been very mature and have been widely used.
Laser Cleaning MouldCleaning of molds.
Each year the world's tire manufacturers manufacture hundreds of millions of tires, and the production process of tire mold cleaning must be rapid and reliable to save downtime. Traditional cleaning methods include sandblasting, ultrasonic or carbon dioxide cleaning, etc., but these methods usually must be performed after several hours of cooling the high-heat mold, and then moved to the cleaning equipment for cleaning. Cleaning takes time, and can easily damage the accuracy of the mold. Chemical solvents and noise will also produce safety and environmental issues. The use of laser cleaning method, because the laser can use optical fiber to transmit, so it is flexible in use; because the laser cleaning method can connect the optical fiber and the light guide to the mold's dead corner or parts that are not easy to remove for cleaning, it is easy to use; because rubber does not gasify, it will not produce toxic gases, affecting the safety of the working environment. Laser cleaning tire mold technology has been adopted in large numbers in the tire industry in Europe and the United States. Although the initial investment cost is high, it can save standby time, avoid mold damage, ensure work safety and save raw materials, quickly recovering the gains. According to laser cleaning equipment in the tire company production line cleaning test shows that only 2 hours can be used to clean a set of large load tire mold online. Compared with conventional cleaning methods, the economic benefits are obvious.
Food industry molds on the anti-adhesive elastic film layer needs to be replaced regularly to ensure hygiene, and without chemical reagents, laser cleaning is also particularly suitable for this application.
Laser Cleaning WeaponCleaning of weapons and equipment.
Laser cleaning technology is widely used in the maintenance of weapons. The use of laser cleaning system can efficiently and quickly remove rust and corrosion, pollutants, and can be selected for the removal of parts to achieve the automation of cleaning. Using laser cleaning, not only is the cleanliness higher than the chemical cleaning process, but also there is almost no damage to the surface of the object. By setting different parameters, you can also form a dense oxide protective film or molten metal layer on the surface of metal objects to improve surface strength and corrosion resistance. Laser removal of waste materials is basically non-polluting to the environment and can also be operated at a distance, effectively reducing the health damage to the operator.
In Europe laser cleaning systems have long been used in the aviation industry. The surface of the aircraft after a certain period of time needs to be repainted, but before painting the original old paint needs to be completely removed. The traditional mechanical paint removal method is prone to damage the metal surface of the aircraft, which brings hidden danger to safe flight. Using multiple laser cleaning systems, the surface paint of an A320 Airbus can be completely removed within two days, and it will not damage the metal surface.
The cleaning of the building facade.
With the rapid development of China's economy, more and more skyscrapers are being established, and the building facade cleaning problems are increasingly prominent. LASERLASTE laser cleaning system, through the longest 70 meters of optical fiber, provides a good solution for cleaning the building facade. It can effectively clean a variety of stone, metal, glass pollutants, and is many times more efficient than conventional cleaning. It can also remove black spots and color spots on various stones on the building. LASERLASTE laser cleaning system in Songshan Shaolin Temple on the building, stone monument cleaning test shows that the use of laser cleaning to protect the ancient building to restore the appearance to very good results.
Cleaning in the electronics industry
Electronics industry using laser removal of oxide: electronics industry needs high-precision decontamination, especially suitable for the use of laser to remove oxide. In the circuit board before welding, component pins must be thoroughly de-oxidized to ensure the best electrical contact, and the decontamination process also cannot damage the pins. Laser cleaning can meet the requirements of use, and is highly efficient, requiring only one laser irradiation per pin.
Precision machinery industry in the precise de-esterification cleaning.
Precision machinery industry often needs to remove esters and mineral oil used to lubricate and prevent corrosion from parts. Usually, chemical methods are used, and chemical cleaning often leaves residues. Laser de-esterification can completely remove esters and mineral oil without damaging the surface of the parts. The contaminant removal is accomplished by shock waves, which are formed by the explosive vaporization of thin layers of oxide on the part surface, resulting in the removal of contaminants, rather than by mechanical interaction. Complete material de-esterification is used for the cleaning of mechanical parts in the aerospace industry. Mechanical parts processing of oil ester removal can also be used for laser cleaning.
Nuclear Laser CleaningNuclear power plant reactor pipeline cleaning.
Laser cleaning systems are also used in the nuclear power plant reactor pipeline cleaning. It uses optical fiber to direct the high power laser beam into the reactor, directly removing radioactive dust, and the cleanup of the material is convenient. And because it is operated from a distance, it can ensure the safety of the staff.
In summary, laser cleaning plays an important role in many fields, and can play an important role in automobile manufacturing, semiconductor wafer cleaning, precision parts processing and manufacturing, military equipment cleaning, building facade cleaning, heritage protection, circuit board cleaning, precision parts processing and manufacturing, liquid crystal display cleaning, chewing gum residue removal and other fields.
Types of Laser Cleaning
There are four main laser cleaning methods.
laser dry cleaning method, that is, direct radiation decontamination by pulsed laser.
laser + liquid film method, that is, first depositing a layer of liquid film on the surface of the substrate, and then decontaminating with laser radiation.
laser + inert gas method, that is, while laser radiation, inert gas is blown to the surface of the substrate, and when the dirt is stripped from the surface it will be immediately blown away from the surface by the gas, in order to avoid recontamination and oxidation of the surface.
The use of laser to loosen the dirt, and then cleaned with non-corrosive chemical methods.
The most commonly used are the first 3 methods. The fourth method is only seen in the cleaning of stone artifacts.
Internationally, the application of laser cleaning technology for stone materials has a history of more than a decade. In China, the stone material laser cleaning started late. Due to the investment in laser equipment is still relatively expensive, the universal application is somewhat difficult. However, laser cleaning technology has the advantages that traditional cleaning methods cannot compare, and with the continuous improvement of technology and equipment batch production, laser cleaning technology will play an important role in the cleaning of stone materials industry.
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