The working device of laser cladding equipment mainly includes laser, feeding device, cladding nozzle, processing platform and control system. For the entire laser cladding equipment, the cladding nozzle device is the most important part of the entire equipment, its main role is the transmission, focusing, transformation of the laser beam and the synchronous transmission of the cladding powder. The key technologies of the cladding nozzle are the laser shaping and transforming focusing, the transmission and injection convergence of cladding materials and the coupling of optical materials. The second is the laser, and now the main lasers to be used are carbon dioxide lasers, YAG lasers and semiconductor lasers. Carbon dioxide laser is now the most widely used laser in China, and it is easier to achieve high power, but it has the disadvantages of too large volume and high unit energy consumption. Due to the development of technology, the utilization rate of YAG lasers is constantly increasing, which can achieve fiber transmission and improve the flexibility of parts. The advantages of semiconductor lasers are high electro-optical conversion rate, low equipment price, small size, lower maintenance cost, more suitable for use and a series of advantages.
Advantages and disadvantages of laser cladding
1. Advantages of laser cladding
Laser cladding generally has high hardness, wear resistance, corrosion resistance, oxidation resistance and other characteristics, especially corrosion resistance, which is of great help to extend the life of materials, save expensive metals, save resources, and no environmental pollution problems. Compared with other traditional substrate surface modification methods, the dilution rate of the cladding layer composed of laser cladding is lower (generally 5% ~ 8%), and it is easy to form a thinner cladding layer. The use of this method not only reduces the cost, but also improves the cladding efficiency. Laser cladding has the characteristics of small heat-affected zone and small deformation, and its cooling rate is very fast (102 ~ 106 K/s), which tends to form dense structures. At present, the laser cladding process is controlled by computer, using digital and fully automated control, and the process parameters are more stable in the operation process, the prepared cladding layer is more uniform, and the error rate is lower. Laser cladding is widely used in aerospace, electric power, automobile, ship, oil and other fields. Laser cladding technology can be nearly any metal or ceramic material on a metal or alloy.
2. Shortcomings of laser cladding
(1) Easy to produce pores. In the process of cladding, the gas in the molten pool is too late to discharge, which will lead to the formation of pores in the cladding layer. For the self-fluxing substrate, because it contains a large amount of silicon-boron deoxidizer, the deoxidation reaction will occur first in the cladding process, producing the corresponding borosilicate compounds, which can insulate the air. When the cladding heating time is long enough, the deoxidation reaction can be fully carried out and no gas holes will be formed. However, the laser cladding heating time is short and the cooling rate is fast, and the deoxygenation reaction is not sufficient, so these deoxidizers can not produce effects, and it is easy to form pores. Generally speaking, stomata are almost difficult to avoid, and can only be controlled with some measures. Common methods include preventing the alloy powder from oxidizing before use, drying the cladding material before use, and so on.
(2) Easy to crack. In the process of cladding, melting, solidification and cooling all occur in a short period of time, and various stresses, such as thermal stress and structural stress, will remain. In addition, if the process parameters are set improperly, cracks will also occur. According to the existing research results, there are several methods to eliminate cracks in the process of cladding: Reasonable composition of cladding materials. Correct selection of process parameters and cladding technology.Add a coating on the surface of the substrate to improve the wettability of the cladding layer.The cladding process is optimized based on the stress action characteristics of the cladding layer.
(3) Lack of uniform standards. Laser cladding materials have not formed a special material system, and there is no uniform standard in the use of cladding materials, resulting in rising costs and reducing economic benefits. In addition, the lack of a unified process parameter standard makes communication between laboratories and companies difficult.
Improve the selection of surface corrosion resistance laser cladding materials
Cladding material is one of the main factors affecting cladding layer. The performance of cladding layer is mainly determined by cladding material. Since the appearance of laser cladding technology, the choice of cladding material has been paid much attention by researchers.
1. Ni-based self-fluxing alloy powder
Nickel-based self-melting powder has good corrosion resistance, and its price is more moderate, so it is also the most used in research. It is suitable for substrates that need to improve heat resistance corrosion, and can be divided into Ni-B-Si and Ni-Cr-B alloy series at this stage. The content of nickel is about 75%, the content of chromium is about 15%, and the content of silicon and boron is about 6%. The synthesized alloy powder not only has significantly higher corrosion resistance, but also has relatively high cost performance.
2. Cobalt-based self-fluxing alloy powder
Cobalt itself has good corrosion resistance, and the alloy powder formed by cobalt and chromium has carbides such as Cr7C3 and borides such as Cr2B. Cobalt has good corrosion resistance, chromium also has good oxidation resistance, so from the point of view of its material characteristics, it is suitable for corrosion resistance with laser cladding material, and it also contains nickel, chromium, carbon and iron, but also has the advantage of reducing the generation of cracks. Chabrol et al. found through experiments that cobalt based materials have the advantages of improving the interface stress state and increasing the bond strength. However, its cost is relatively high compared to other materials.
3. Iron-based self-fluxing alloy powder
Iron-based self-fluxable alloy powder is mostly used in cast iron and low carbon steel, and its biggest advantage is low price and anti-wear. But it is very easy to oxidize, even if the addition of boron, nickel, chromium and other elements can not make up for its easy oxidation characteristics. Therefore, its versatility as a corrosion resistant cladding material is poor.
In summary, the above three kinds of alloy powder have their own advantages and disadvantages, should be selected according to the actual situation, in the field of corrosion resistance, considering the cost performance of the case, nickel-based self-fluxable alloy powder is a more suitable choice.
4. Other metal powder
In addition to the above three kinds of metal powder, there are several other materials, such as titanium base, copper base, aluminum base, magnesium base and chromium base, as well as intermetallic compound cladding materials. These materials are made use of their special properties to achieve various functions, such as corrosion resistance, oxidation resistance, wear resistance, etc. For example, the researchers sent aluminum powder through the laser to the surface of the substrate, and also obtained a coating with good performance. There is also magnesium based powder, which is more used for laser cladding of magnesium alloy as the substrate, so that the corrosion resistance of the surface of the magnesium substrate has been significantly improved, especially in the experiment, the researcher used sodium chloride solution to carry out corrosion tests and found that its corrosion resistance has been greatly improved.
5. Ceramic powder
Ceramic powder mainly includes oxide ceramic powder and silicide ceramic powder, among which oxide ceramic powder is often used in laser cladding. Because it can effectively improve the wear resistance, corrosion resistance and oxidation resistance of the matrix, it is often used as a corrosion resistant cladding layer. However, due to the large difference between the physical and chemical properties of ceramic powder and metal on the surface of the substrate, the cladding layer is easy to crack and fall off. Although the researchers added CaO, SiO2 and other substances to the transit layer and cladding layer, which alleviated this situation, it did not completely solve the problem of cracks and falling off the ceramic cladding layer.
6. Composite powder
Composite powder is mainly composed of two or more kinds of materials with different compositions and different properties of the powder, mainly refers to carbide, boride, nitride, oxide and other high melting point hard ceramic materials and gold materials mixed preparation of powder. Under the action of laser composite powder, it can better combine the good toughness of metal and the excellent characteristics of corrosion resistance, wear resistance and high temperature resistance of ceramics, and the phenomena of burning loss and volatilization of materials can be effectively controlled, which is a hot research direction in the field of laser cladding. Among them, carbide alloy powder and oxide alloy powder are the most studied and applied. The carbide particles in the composite powder can be added directly to the laser melt pool or mixed with the metal powder to the laser melt pool, but the more effective way is to add in the form of metal coated compound powder (such as nickel coated carbide, cobalt coated carbide).
Xi'an Guosheng Laser Technology Co., Ltd. is a high-tech enterprise specializing in R&D, manufacturing and sales of automatic laser cladding machine, high-speed laser cladding machine, laser quenching machine, laser welding machine and laser 3D printing equipment. Our products are cost-effective and sold domestically and abroad. If you're interested in our products, please contact us at bob@gshenglaser.com.