Cutting-edge Applications | Why Will Laser Cleaning Become Trend?

October 22, 2021
Latest company news about Cutting-edge Applications | Why Will Laser Cleaning Become Trend?


Development and principle of laser cleaning


The traditional industrial cleaning methods mainly include high-pressure water, chemical reagent, ultrasonic and mechanical grinding, but these cleaning methods have the problems of damaging the substrate, poor working environment, pollution, incomplete cleaning at some positions and high cleaning cost. With the aggravation of environmental pollution, scholars all over the world are actively developing new cleaning technologies with energy conservation, environmental protection and high efficiency. Because laser cleaning technology has many advantages, such as low damage of matrix materials, high cleaning accuracy, zero emission and no pollution, it is gradually valued and favored by academia and industry. There is no doubt that the application of laser cleaning technology to the dirt cleaning of metal surface has a very broad prospect.

Development history and present situation of laser cleaning technology

In the 1960s, the famous physicist Schawlow first proposed the concept of laser cleaning, and then applied the technology to the repair and maintenance of ancient books. The decontamination range of foreign laser cleaning is very wide, from thick rust layer to fine particles on the object surface, including the cleaning of cultural relics and works of art, the removal of rubber dirt on the surface of tire mold, the removal of silicone oil pollutants on the surface of gold film and high-precision cleaning of microelectronics industry. In China, laser cleaning technology really began in 2004. China began to invest a lot of human and material resources to strengthen the research on laser cleaning technology. In recent ten years, with the development of advanced lasers, from inefficient and bulky carbon dioxide lasers to lightweight and compact fiber lasers; From continuous output laser to nanosecond, picosecond and femtosecond short pulse laser; From visible light output to long wave infrared light and short wave ultraviolet light output... Lasers have made a leap in energy output, wavelength range, laser quality and energy conversion efficiency. The development of laser naturally promotes the rapid development of laser cleaning technology. Laser cleaning technology has achieved fruitful results in theory and application.

Principle of laser cleaning technology

The process of pulsed laser cleaning depends on the characteristics of the optical pulse generated by the laser, and is based on the photophysical reaction caused by the interaction between high-intensity beam, short pulse laser and pollution layer. Its physical principle can be summarized as follows:
a) The beam emitted by the laser is absorbed by the pollution layer on the surface to be treated;
b) The absorption of large energy forms rapidly expanding plasma (highly ionized unstable gas) and produces shock waves;
c) The shock wave turns the pollutants into fragments and is removed;
d) The light pulse width must be short enough to avoid heat accumulation that destroys the treated surface;
e) Experiments show that when there are oxides on the metal surface, the plasma occurs on the metal surface.

The plasma is generated only when the energy density is higher than the threshold, which depends on the contaminated layer or oxide layer removed. This threshold effect is very important for effective cleaning while ensuring the safety of the substrate material. There is a second threshold for the emergence of plasma. If the energy density exceeds this threshold, the base material will be destroyed. In order to effectively clean the substrate material on the premise of ensuring the safety of the substrate material, the laser parameters must be adjusted according to the situation, so that the energy density of the optical pulse is strictly between the two thresholds.

Advantages of laser cleaning

Compared with traditional cleaning methods such as mechanical friction cleaning, chemical corrosion cleaning, liquid solid strong impact cleaning and high-frequency ultrasonic cleaning, laser cleaning has five obvious advantages:

  • Environmental protection advantages: laser cleaning is a "green" cleaning method. It does not need to use any chemical agent and cleaning solution. The cleaned waste is basically solid powder, small volume, easy to store, recyclable, no photochemical reaction and no pollution.
  • Effect advantage: the traditional cleaning method is often contact cleaning, which has mechanical force on the surface of the cleaned object, damages the surface of the object or the cleaning medium is attached to the surface of the cleaned object, which cannot be removed and produces secondary pollution. The non-grinding, non-contact and non-thermal effect of laser cleaning will not damage the substrate, so that these problems can be solved.
  • Control advantage: laser can be transmitted through optical fiber and cooperate with manipulator and robot to realize remote operation conveniently. It can clean parts that are not easy to reach by traditional methods, which can ensure personnel safety in some dangerous places.
  • Convenience advantage: laser cleaning can remove various types of pollutants on the surface of various materials and achieve cleanliness that conventional cleaning cannot achieve. It can also selectively clean the pollutants on the material surface without damaging the material surface.
  • Cost advantage: laser cleaning is fast, efficient and saves time; At this stage, although the one-time investment in the purchase of laser cleaning system is high in the early stage, the cleaning system can be used stably for a long time and has low operation cost. More importantly, it can easily realize automatic operation. It can be predicted that the cost of laser cleaning system will be greatly reduced in the future, so as to further reduce the cost of using laser cleaning technology.

Laser cleaning methods can be divided into the following three categories:


1. Laser dry cleaning

Laser radiation is used for direct decontamination. After the laser is absorbed by objects or dirt particles, it will produce vibration, so as to separate the matrix and pollutants. There are two main ways to remove dirt particles in laser dry cleaning: one is the instantaneous thermal expansion of the substrate surface, resulting in vibration, so that the particles adsorbed on the surface can be removed. The other is that the particles leave the substrate surface due to the thermal expansion of the particles themselves.


2. Laser wet cleaning

Laser wet cleaning is to evenly cover a layer of liquid medium film on the surface of the substrate to be cleaned, and then remove the stains with laser radiation. According to the absorption of laser by dielectric film and substrate, wet cleaning can be divided into strong substrate absorption, strong dielectric film absorption and common absorption of dielectric film substrate. During strong matrix absorption, after the matrix absorbs laser energy, the heat is transferred to the liquid medium film, the liquid layer at the interface between the matrix and the liquid is overheated and boiling, and the liquid layer and stains are removed together.

3. Laser + inert gas cleaning
At the same time of laser radiation, inert gas is blown to the workpiece surface. When the pollutants are stripped from the surface, they are blown far away from the surface by gas to avoid pollution and oxidation of the clean surface.

Application fields of laser cleaning
With the development of laser cleaning technology, laser cleaning technology has been popularized to many industries in industrial application, as shown below:

  1. Microelectronic field: semiconductor components, microelectronic devices, memory templates, etc.;
  2. Field of cultural relic’s protection: stone carvings, bronzes, glass, oil paintings and murals;
  3. Abrasive cleaning: rubber mold, composite mold, metal mold, etc.;
  4. Surface treatment: hydrophilic treatment, surface roughening, weld treatment before and after welding, etc;
  5. Paint and rust removal: aircraft, ships, weapons and equipment, bridges, metal pressure vessels, metal pipelines, etc; Aircraft parts, electrical product parts, etc.;
  6. Other: Urban graffiti, printing roller, building exterior wall, nuclear industry, etc.

Laser cleaning will become the general trend of cleaning market development. Although at present, laser cleaning cannot completely replace the traditional cleaning technology, with the progress of science and technology and the improvement of environmental protection requirements, laser cleaning will become the general trend of the development of the global cleaning market. By developing new laser cleaning systems and equipment and optimizing the cleaning process, improving the cleaning efficiency, reducing the cleaning cost, reducing the damage of the surface to be cleaned, and realizing the green, efficient and automatic cleaning process of metal surface must be the demand of the future market. Shenzhen Herolaser Equipment Co., Ltd. is an enterprise engaged in the R & D, production and sales of laser cleaning machines. At present, the 100W-2000W pulse laser cleaning machines launched by Herolaser in the field of laser cleaning have been widely used in the fields of surface treatment, mold cleaning, paint and rust removal and other hardware manufacturing, automobile and rail transit.