Laser surface treatment uses a high-power-density laser beam to heat the surface of a material in a non-contact manner. The process technology of surface modification is realized by means of conduction cooling on the surface of the material itself. It is of great benefit in improving the mechanical properties and physical properties of the material surface, as well as improving the wear resistance, corrosion resistance and fatigue resistance of parts. In recent years, laser surface treatment technologies such as laser cleaning, laser quenching, laser alloying, laser shock strengthening, and laser annealing, as well as laser additive manufacturing technologies such as laser cladding, laser 3D printing, and laser electroplating, have ushered in broad application prospects.
01 Laser Cleaning
Laser cleaning is a new type of surface cleaning technology that is currently developing rapidly. It uses high-energy pulsed laser beams to irradiate the surface of the workpiece, so that the dirt, particles or coating on the surface evaporate or expand and peel off instantly, so as to achieve a clean process. Laser cleaning is mainly divided into processes such as rust removal, oil removal, paint removal, and coating removal; it is mainly used in metal cleaning, cultural relic cleaning, construction cleaning, etc. Based on its comprehensive functions, precise and flexible processing, high efficiency and energy saving, green environmental protection, no damage to the substrate, intelligence, good cleaning quality, safety, and wide application range, it is becoming more and more popular in various industrial fields.
Compared with traditional cleaning methods such as mechanical friction cleaning, chemical corrosion cleaning, liquid and solid impact cleaning, and high-frequency ultrasonic cleaning, laser cleaning has obvious advantages.
02 Laser Quenching
Laser quenching uses a high-energy laser as a heat source to heat and cool the metal surface quickly, complete the quenching process in an instant, obtain a high-hardness, ultra-fine martensite structure, improve the hardness and wear resistance of the metal surface, and form compressive stress on the surface , improve fatigue resistance. The core advantages of this process include small heat-affected zone, small deformation, high degree of automation, good flexibility of selective quenching, high hardness of refined grains, and intelligent environmental protection. For example, the laser spot is adjustable, which can quench the position of any width; secondly, the laser head cooperates with the multi-axis robot linkage, which can quench the designated area of complex parts. Another example, laser quenching is extremely hot and rapid cooling, and the quenching stress and deformation are small. The deformation of the workpiece before and after laser quenching is almost negligible, so it is especially suitable for surface treatment of parts with high precision requirements.
At present, laser quenching has been successfully applied to the surface strengthening of wearing parts in the automotive industry, mold industry, hardware tools, and machinery industries, especially in improving the service life of wearing parts such as gears, shaft surfaces, guide rails, jaws, and molds. , the effect is remarkable. The characteristics of laser quenching are as follows:
1) Laser quenching is rapid heating, self-excited cooling, does not require furnace insulation and coolant quenching, is a non-polluting, green and environmentally friendly heat treatment process, and can easily perform uniform quenching on the surface of large molds;
2) Due to the fast laser heating speed, small heat-affected zone, and surface scanning heating and quenching, that is, instantaneous local heating and quenching, the deformation of the processed mold is very small;
3) Due to the small divergence angle of the laser beam, it has good directivity, and can accurately and locally quench the mold surface through the light guide system;
4) The hardened layer depth of laser surface quenching is generally 0.3-1.5mm.
03 Laser Annealing
Laser annealing refers to the heat treatment process that uses laser to heat the surface of the material, expose the material to high temperature for a long time, and then slowly cool it down. The main purpose of this process is to release stress, increase material ductility and toughness, and produce special microstructure. It is characterized by the ability to adjust the matrix structure, reduce hardness, refine grains and eliminate internal stress. In recent years, laser annealing technology has also become a new technology in the semiconductor processing industry, which can greatly improve the integration of integrated circuits.
04 Laser Shock Hardening
Laser shock strengthening technology is a high-tech technology that uses plasma shock waves generated by strong laser beams to improve the fatigue resistance, wear resistance and corrosion resistance of metal materials. It has outstanding advantages such as no heat-affected zone, efficient energy utilization, ultra-high strain rate, strong controllability and remarkable strengthening effect. At the same time, laser shock strengthening has the characteristics of deeper residual compressive stress, better microstructure and surface integrity, better thermal stability and longer life. In recent years, this technology has been developed rapidly, and it is very useful in the fields of aerospace, national defense and military industry. In addition, the function of the coating is mainly to protect the workpiece from being burned by the laser and to enhance the absorption of laser energy. Currently, commonly used coating materials include black paint and aluminum foil.
Laser peening (LP), also known as laser shock peening (LSP), is a process applied in the field of surface engineering, which uses pulsed high-power laser beams to generate residual stress in materials to improve the damage resistance of the material surface ( Such as wear resistance and fatigue resistance), or increase the strength of the thin section of the material to strengthen the surface hardness of the material.
Unlike most material processing applications, LSP does not use laser power for heat treatment to achieve the desired effect, but instead uses beam impingement for machining. The high-power laser beam hits the target workpiece surface with high-power short pulses.
The beam hits the metal workpiece, instantly vaporizing the workpiece into a thin plasma state and applying shock wave pressure to the workpiece. A thin layer of opaque facing material is sometimes added to the workpiece in place of metal evaporation. For pressurization, other transparent cladding materials or inertial disruptors are used to trap the plasma (usually water).
The plasma produces a shock wave effect that reshapes the microstructure of the workpiece surface at the point of impact, followed by a chain reaction of metal expansion and compression. The deep compressive stresses created by this reaction extend component life.
05 Laser Alloying
Laser alloying is a new type of surface modification technology, which can be used to prepare amorphous single nanocrystalline reinforced cermet composite coatings on the surface of structural parts by using the characteristics of high energy density laser beam heating and condensation rate according to different service conditions of aerospace materials. , to achieve the purpose of surface modification of aerospace materials. Compared with laser alloying technology, laser cladding technology has the characteristics of small dilution rate of base material to molten pool, small heat-affected zone, small deformation of workpiece due to heat, and low scrap rate of workpiece after laser cladding treatment. Laser cladding can significantly improve the surface properties of materials, and can repair worn and failed materials. It has the characteristics of high efficiency, fast speed, environmental protection and pollution-free, and good performance of the workpiece after treatment.
06 Laser Cladding
Laser cladding technology is also one of the new surface modification technologies representing the development direction and level of surface engineering. Laser cladding technology has become a research hotspot in contemporary titanium alloy surface modification due to its advantages of no pollution and the prepared coating is metallurgically bonded to the substrate. The use of laser cladding ceramic coating or ceramic particle reinforced composite coating is an effective way to improve the wear resistance of titanium alloy surface. Select the appropriate material system according to the actual working conditions, and use laser cladding technology to achieve the best process requirements. Laser cladding technology can repair various failed parts, such as aeroengine blades, etc.
The difference between laser surface alloying and laser surface cladding is that laser surface alloying is to fully mix the added alloy elements and the surface layer of the substrate in a liquid state to form an alloyed layer; while laser surface cladding is to make the pre-coating All of them are melted and the surface of the substrate is slightly fused, so that the cladding layer and the substrate material form a metallurgical bond while keeping the composition of the cladding layer basically unchanged. Laser alloying and laser cladding technologies are mainly used to improve the surface wear resistance, corrosion resistance and grade resistance of titanium alloys.
At present, laser cladding technology has been widely used in the repair and modification of metal surfaces. However, although traditional laser cladding has advantages and characteristics such as flexible processing, special-shaped repair, and custom additive materials, the work efficiency is low. For some production fields The required large-scale and rapid production and processing needs still cannot be met. In order to meet the needs of high-volume high-speed production and improve the efficiency of cladding, high-speed laser cladding technology came into being.
The high-speed laser cladding technology can realize a dense and defect-free cladding layer. The surface quality of the cladding layer is dense, and it is metallurgically combined with the base material, without opening defects, and the surface is smooth and flat. It can not only process on the rotary body, but also process on the plane and complex curved surface. Through continuous technical optimization, this technology can be widely used in coal, metallurgy, offshore platforms, papermaking, household appliances, automobiles, ships, petroleum, aerospace industries, and become a green remanufacturing process that can replace traditional electroplating technology.
07 Laser Engraving
Laser engraving is a laser processing process that uses numerical control technology as the basis to project a high-energy laser beam onto the surface of the material, and uses the thermal effect generated by the laser to produce a clear pattern on the surface of the material. The physical deformation of the processed material under the irradiation of laser engraving for instant melting and gasification can make laser engraving realize the processing purpose. Laser engraving is to use laser to engrave text on the object. The characters engraved by this technology have no nicks, the surface of the object is smooth and flat, and the writing will not wear out. Its features and advantages include: safe and reliable; precise and meticulous, the precision can reach 0.02mm; environmental protection, processing saves materials; high speed and fast, high-speed engraving according to the output pattern; low cost, not limited by the number of processing, etc.
08 Laser 3D Printing
The process adopts laser cladding technology, which uses laser to irradiate the powder flow delivered by the nozzle to directly melt the elemental or alloy powder. After the laser beam leaves, the alloy liquid is rapidly solidified to realize rapid alloy prototyping. At present, it has been widely used in industrial modeling, machinery manufacturing, aerospace, military, construction, film and television, home appliances, light industry, medicine, archaeology, culture and art, sculpture, jewelry and other fields.
09 Typical Industrial Applications Of Laser Surface Treatment And Remanufacturing
At present, laser surface treatment and additive manufacturing technology, technology and equipment are widely used in metallurgy, mining machinery, molds, petroleum power, hardware tools, rail transit, aerospace, machinery and other industries.
10 Application of laser plating technology
Laser electroplating is an emerging high-energy beam electroplating technology, which is of great significance to the production and repair of microelectronic devices and large-scale integrated circuits. At present, although the principle of laser electroplating, laser ablation, plasma laser deposition and laser jetting are still under study, its technology has been put into practical use. When a continuous laser or pulsed laser is irradiated on the surface of the cathode in the electroplating pool, not only can the deposition rate of metal be greatly increased, but also the movement trajectory of the laser beam can be controlled by computer to obtain the expected unshielded coating of complex geometry.
The application of laser plating in practice is mainly based on the following two characteristics:
① The speed in the laser irradiation area is much higher than the plating speed in the body (about 103 times);
②The control ability of the laser is strong, which can make the necessary part of the material analyze the required amount of metal. Ordinary electroplating occurs on the entire electrode substrate, the electroplating speed is slow, and it is difficult to form complex and fine patterns. Using laser plating can adjust the laser beam to micron size, and carry out unshielded drawing on micron size. This type of high-speed tracing is increasingly practical for circuit design, circuit repair, and localized deposition on microelectronic connector components.
Compared with ordinary electroplating, its advantages are:
(1) Fast deposition speed, such as laser gold plating up to 1μm/s, laser copper plating up to 10μm/s, laser spray gold plating up to 12μm/s, laser spray copper plating up to 50μm/s;
(2) Metal deposition only occurs in the laser irradiation area, and local deposition coatings can be obtained without shielding measures, thus simplifying the production process;
(3) The bonding force of the coating is greatly improved;
(4) Easy to realize automatic control;
(5) Saving precious metals;
(6) Save equipment investment and processing time.
When a continuous laser or pulsed laser is irradiated on the surface of the cathode in the electroplating pool, it can not only greatly increase the deposition rate of metal, but also can control the trajectory of the laser beam by computer to obtain the unshielded coating of the expected complex geometry. The current new technology of laser jet enhanced electroplating combines laser enhanced electroplating technology with electroplating solution spray, so that the laser and the plating solution are simultaneously shot to the surface of the cathode, and its mass transfer rate is much higher than that of microscopic stirring caused by laser irradiation. , so as to achieve a very high deposition rate.
11 Future Development And Innovation
Looking forward to the future, the development direction of laser surface treatment and additive manufacturing equipment can be summarized as follows:
- High efficiency - high processing efficiency, to meet the rapid production rhythm of modern industry;
- High performance - the equipment has diversified functions, stable performance, and is suitable for different working conditions;
- High intelligence - the level of intelligence is continuously improved, and there is less manual intervention;
- Low cost - controllable equipment cost and reduced cost of consumables;
- Customization - personalized customization of equipment, precise after-sales service;
- And composite - the combination of laser technology and traditional processing technology.
