Laser surface treatment is a non-contact treatment method. By designing and laser improving the surface of the workpiece, its surface performance is improved, and the deformation of the workpiece is minimal. It uses laser beams to quickly and locally heat the workpiece to achieve local rapid heating or rapid cooling, and can be processed in atmosphere, vacuum and other environments. By changing the laser parameters, different surface treatment process problems can be solved.
The surface properties of the workpiece can be improved by using the structure change of the material itself or introducing other materials during the laser scanning process. This technology can selectively treat the surface of the workpiece, which is beneficial to obtain a higher surface while maintaining sufficient toughness and strength of the workpiece as a whole. Specific performance, such as wear resistance, corrosion resistance and fatigue resistance, oxidation resistance, etc.
So, what are the laser surface treatment technologies?
According to the purpose of surface treatment, it is divided into surface modification treatment and removal treatment; laser surface modification treatment includes laser glazing, laser remelting, laser alloying, and laser coating; laser removal treatment includes laser cleaning.
1. Laser remelting treatment
Laser remelting is a technology that uses a laser beam with a higher power density (10-10W/cm2) to scan the metal surface to melt the surface metal, and then rapidly cools and solidifies it. During the laser surface microcrystallization treatment, due to the large degree of undercooling caused by self-exciting cooling, the rapid solidification of the alloy will lead to solute traps and non-diffusion crystallization, forming a fine microcrystalline structure. Laser surface remelting to prepare a microcrystalline modified layer can improve the wear resistance and fatigue resistance of the material surface. For some eutectic alloys, even an amorphous surface layer can be obtained, which has excellent corrosion resistance.
2. Laser alloying
Laser energy is used to heat the surface of a local area of a material to a certain temperature or form a thin molten layer, and to change the chemical composition of the surface by diffusion or addition of alloy elements or chemical reactions to improve the mechanical, physical and chemical properties of the material surface. It has the advantages of local processing, low substrate deformation, no damage to the substrate performance, high efficiency and rapid heating, etc., especially suitable for important parts of the workpiece, such as the joint line of the mold, the partial surface of the valve lifter and the camshaft . There are many methods of pre-alloying in laser surface alloying technology, including workpiece surface electroplating, vacuum evaporation, pre-powder layer, thick film placement, ion implantation, powder spraying, wire feeding and application of reactive gases.
3. Laser coating
In addition to the metallurgical combination of the substrate and the molten coating material, the laser coating is rarely diluted by the substrate material and basically keeps its original composition unchanged. The commonly used coating material for laser coating is alloy powder, and it can also be a mixture of different metal shavings and alloy powder. According to the supply method of alloy powder, it can be divided into two types of coating: one is preset powder laser coating, that is, a certain thickness of alloy powder layer is preset on the substrate before laser treatment; the other is powder feeding method. Laser coating, the powder is sent to the active area of laser and material with inert gas.
4. Laser glazing
Laser glazing is also known as laser glazing. The laser energy density used in it is 10-10W/cm2, which makes the metal surface melt quickly and forms a very thin layer of melting on the surface. When the laser is quickly removed, the metal itself will melt. The "self-quenching" zone is carried out, and the cooling rate is as high as 10-10°C/S. Through this rapid melting-solidification process, a special amorphous layer (metallic glass) is produced on the metal surface. Laser glazed electronic, electromagnetic and other electrical materials are ideal for measuring instruments.
5. Laser removal
Laser removal is to use laser to instantly evaporate or peel off the dirt, rust or coating on the surface of the workpiece, and effectively clean the surface of the workpiece at high speed. The laser cleaning process does not use organic solvents, is pollution-free and noise-free, and is a "green" process.
6. Laser cleaning
The high-energy laser beam is used to irradiate the surface of the workpiece, so that the dirt, rust spots or coatings on the surface are evaporated or peeled off instantly, and the pollutants or coatings on the surface are effectively removed at high speed. Laser cleaning belongs to dry cleaning, does not require organic solvents, no waste liquid discharge, less residue, will not cause environmental pollution, and can effectively remove submicron particles adsorbed on the surface of objects that are difficult to remove by other methods. This technology has high flexibility, good controllability, and is easy to select and locate precision cleaning, and it is easy to remote control and clean difficult-to-reach or dangerous places.
7. Laser honing
Laser honing, also known as laser micro-modeling technology, is to apply a laser beam with a certain energy density on the working surface of the cylinder wall to carry out surface micro-geometric structure modeling according to the lubricating performance requirements of the engine to form a continuous, continuous surface that matches the lubricating performance requirements. Uniform oil passages and concave cavities for storage and delivery of lubricating oil with a certain density, width, depth, angle, and shape form a "miniature pressure chamber" and produce a stable dynamic lubricating film with a certain thickness. Laser honing technology can significantly improve the lubrication condition of the cylinder during operation, and can greatly improve the performance of the internal combustion engine. It has a series of advantages: prolonging the service life, reducing engine oil consumption, reducing catalyst pollution and particle emissions, reducing fuel consumption and piston rings group cost.
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