Research progress of laser cladding application in agricultural machinery repair and strengthening

The market background Compared with high-end manufacturing fields such as industrial machinery, aerospace and automobiles, agricultural machinery manufacturing has always lagged behind them. In order to promote the development of agricultural modernization, it is necessary to strengthen the application of laser cladding technology in repairing and strengthening agricultural machinery. Draw lessons from other fields of advanced technology research results for agricultural machinery repair and strengthening to provide research direction. Therefore, in order to improve the reliability of agricultural machinery in complex soil environment, the following four aspects can be studied: in-situ repair; Improve wear resistance; Improved corrosion resistance; Increase hardness. In situ repair: the use of agricultural machinery is high, the working environment is poor, many agricultural machinery parts in the long-term use of overload operation state, so it is easy to appear plastic deformation, wear, crack, corrosion and other problems. In situ repair is refers to a specific defect parts processing, to restore its original size and laser cladding is one of the major of in situ remediation technologies, because of the repair parts is not easy to deformation, cooling speed, high precision and good performance advantages, has been in the field of agricultural machinery repair has been widely used. For example, gear parts in the process of agricultural machinery operation, will be affected by strong alternating stress, easy to cause flanging, gnawing, deformation and other problems, using laser cladding technology can make the defect of gear to restore the original size. Through the experiments, the gear repaired by laser cladding can not only work normally, but also improve the impact resistance, hardness, wear resistance and other properties of the gear. In addition, shaft parts are also one of the parts that often need to be repaired in agricultural machinery. In addition to the action of alternating stress, axis components will also be affected by friction and wear, and the influence of friction and wear is more significant, which is the main reason for its damage. The working environment of agricultural machinery is relatively bad. In the process of long-term rotation of the internal rotating shaft, high-hardness silt particles infiltrate into it and form wear, thus causing regional deep scratches. The scratches enhance the effect of abrasive particles, and then intensify the damage process, forming a vicious cycle. Using laser cladding technology to repair bearings in situ, the scratches can be filled and the surface morphology of the shaft can be restored. Laser cladding technology produces thin coatings, enabling effective thickness control of cladding coatings to ensure geometric tolerances and dimensional accuracy of repaired parts. Improve wear resistance: wear in agricultural machinery is generally divided into adhesion wear and abrasive wear, among which abrasive wear is the most common. Abrasive wear is the friction between the surface of parts and relatively hard abrasive particles. Direct contact with soil or sand grains during cultivation can cause serious wear and tear. There are many cladding materials to improve wear resistance, among which the iron – based cladding material is the most widely used in the field of agricultural machinery. Fe-base alloy has been widely used because of its similar composition with the base material of agricultural machinery parts, good metallurgical bonding, high wear resistance and low cost of coating. The single iron base alloy also has some disadvantages, such as high melting point, poor self-fusing property, poor oxidation resistance, poor fluidity, and more porosity and slag. Later, in order to improve the iron base alloy, the addition of B and SI elements Fe base self-melting alloy can further improve the wear resistance. In addition, adding rare earth elements into the cladding material can improve the wear resistance of the cladding coating. The cladding alloy powder was mechanically mixed according to the ratio of chemical composition CeO2, and the cladding coating was prepared on the surface of the steel matrix. The cladding coating produced by in-situ reaction generated ceramic hard phase, with compact structure, no pores and cracks, and the wear resistance was significantly improved. Rare earth elements can significantly improve the microstructure of the cladding layer and refine the dendrite structure, among which a reasonable amount of rare earth elements is the key to effectively improve the wear resistance of the cladding layer. Improved corrosion resistance: Agricultural machinery components often work in wet and corrosive environments such as pesticides, fertilizers and organic fertilizers, thus accelerating the damage of agricultural machinery and tools. The composition of laser cladding powder will directly affect the corrosion resistance of cladding layer. In the research and exploration of corrosion resistance, nickel-based self-fusing alloy powder is the most prominent in laser cladding materials, and is widely used in repairing parts requiring corrosion resistance. With the development of the research, it is found that the addition and control of external field conditions have a significant influence on the corrosion resistance of the cladding layer. The Fe60 alloy coating was prepared by laser cladding on the surface of 45 steel with the aid of mechanical vibration and magnetic field. Under the action of the composite field, the content of Fe-Cr solid solution in the coating was effectively increased, and the corrosion resistance of the coating was significantly improved, which provided a direction for further optimization of laser cladding strengthening agricultural machinery technology. Improve hardness: because there will be larger stones and roots under the soil, tilling knives, disk harrows and other tillage components in the process of ploughing and plowing may encounter large impact and damage, which has higher requirements for the hardness of agricultural machinery. Some scholars have conducted a comparative study on the hardness of cladding layers of Fe60 alloy and Ni60 alloy with 45 steel as the matrix material. Under the condition of the same laser power and powder feeding amount, the hardness of Ni60 alloy cladding coating is higher, but there are more cracks defects, while the hardness of Fe60 alloy bonding zone is high, the overall hardness distribution is gentle, forming a good metallurgical bonding, and no obvious defects, compared with the nickel base alloy, the comprehensive properties of iron base alloy powder is ideal. It is more suitable for laser cladding surface treatment of 45 steel. Later, the microstructure and properties of the cladding layer of Fe60 alloy were further studied. The microstructure of the cladding layer of Fe60 alloy is mainly composed of equiaxed crystals, dendritic crystals and columnar crystals rich in Ni, Cr and Si. Proper laser cladding process control can realize the rapid melting and solidification of cladding layer, forming non-equilibrium and sub-crystalline dendritic eutectic structure, Si atom solution strengthening and laser fine grain strengthening, forming smooth, compact and high quality cladding layer with little thermal effect, significantly improving the hardness of coating. In recent years, laser cladding hard phase particles have been widely concerned, including WC, NbC, TiC, Tac and Vc. The addition of WC particles has a positive effect on improving the microhardness of matrix. Ma et al. prepared Ni60/WC composite coating by laser cladding technology. The coating has eutectic structure and high hardness. Hard reinforced metal matrix composite coating has been widely used on the surface of various mechanical parts with wear conditions because of its high hardness and certain plastic strain capacity. Laser cladding technology has accumulated a large number of experimental data and basic theories in the field of high-end manufacturing after nearly half a century of research. However, because of the characteristics of agricultural machinery itself and the complexity of the working object, its manufacturing, repair and strengthening means lag behind the high-end manufacturing field. Therefore, the research and application of laser cladding technology in agricultural machinery repair and strengthening started late, and is basically in the preliminary research stage of coating material preparation technology and wear resistance and corrosion protection. In order to realize the popularization and application of laser cladding technology in the field of agricultural machinery repair and strengthening, the following three directions can be studied in the future: 1. Learn from the research results accumulated in high-end manufacturing industry and combine with the actual production situation of agricultural machinery repair and strengthening to change the current situation of low level and slow development of agricultural machinery design and manufacturing. 2. Research and development of new composite powder suitable for agricultural machinery repair and strengthening. Based on the existing material system and combining with the characteristics of agricultural machinery, the high quality cladding material powder system suitable for different working conditions is designed. 3. Laser cladding is the result of a variety of process parameters, and the best cladding coating can be obtained by selecting the appropriate process parameters. Therefore, the optimization design of process parameters has its very important practical significance. Although the laser cladding technology in the application of agricultural machinery repair and strengthening still exist certain difficulties, but we can believe that, under the joint efforts of scientific research workers, in the near future, laser cladding technology can be out of the lab and is widely used in agricultural machinery repair and reinforcement, for our country’s agricultural mechanization process provides a strong protection.铜焊丝,Copper Welding Rods,铝焊丝,aluminium welding wire,镍焊条,Nickel electrode,药皮焊条,Flux Coated Brazing Welding Rods