Application of Laser Cladding in Parts Repair
With the continuous development of modern science and technology and industry, the working environment of parts and components is becoming more and more complicated, and the requirements for surface performance are getting higher and higher, so the scrap rate of parts is greatly increased. The parts that are usually scrapped due to surface failure are: rotor blades, roller shaft parts, gear parts, joint parts, etc.
Under the condition that the overall performance of the parts meets the working conditions, only the parts with surface damage can be repaired, which can not only restore huge economic and time losses, but also improve the utilization rate of resources.
At present, the repair methods of parts include laser cladding, vacuum brazing, vacuum coating method, tungsten inert gas welding (TIG) and plasma cladding repair methods. Laser cladding is to clad metals or non-metals of various design components according to the working conditions of the workpiece to prepare surface coatings with heat resistance, corrosion resistance, wear resistance, oxidation resistance, fatigue resistance or optical, electrical and magnetic properties. . Laser cladding is a rapid cooling process. During the cladding process, the heat input to the repaired workpiece is small, the heat affected zone is small, the structure of the cladding layer is small, and it is easy to realize automation. Therefore, the laser cladding method is used to repair the rotor. Equal parts have greater advantages than other methods. Laser cladding technology solves a series of technical problems such as thermal deformation and thermal fatigue damage that are unavoidable in traditional electric welding, argon arc welding and other hot working processes, and also solves the traditional electroplating, spraying and other cold working processes. The bonding strength of the coating and the substrate Poor contradiction, which provides a good way for surface repair.
1. Repair of rotor blades
The rotor blade, also known as the moving blade, is a blade that rotates with the rotor at a high speed. The energy conversion between the airflow and the rotor is realized through the high-speed rotation of the blade. The rotor blades are subjected to a large mass inertia force, a large aerodynamic force and vibration load, as well as the corrosion and oxidation of the environmental medium, as well as the erosion of small particles running at high speed, but the processing is more difficult, and the turbine rotor blades are also exposed to high temperatures. working in the state. The rotor blade is a key part that directly affects the performance, reliability and life of the engine, and its working conditions are very harsh and easy to damage, so the requirements for material properties are also greatly improved, and the economic cost of materials is also increased. to a broad market. The application of laser cladding technology on rotor blades has been well studied, which also provides a favorable premise for its application in repair.
(1) Repair of aero-engine blades
At present, most of the aero-engine blades are made of cast nickel-based superalloys and directionally solidified nickel-based superalloys. Cast nickel-based high-temperature blades and directionally solidified blades may have local defects in the production process, such as shrinkage porosity, shrinkage holes and other casting defects.
Laser cladding has the advantages of local heating and low heat input, and at the same time, the ultra-high temperature gradient of laser cladding is conducive to the directional solidification growth of materials. Therefore, extensive research has been carried out on the repair of high value-added blades by laser cladding technology at home and abroad, and it has been successfully applied in industry. At the same time, the laser cladding technology was compared with surfacing welding, TIG welding and plasma cladding.
(2) Repair of steam turbine blades
Turbine blades convert the linear motion of high temperature and high pressure gas into the rotation of the turbine shaft in the power industry. There are two main failure modes of steam turbine blades: one is blade fracture, which mainly occurs at the root of the blade, and this failure is irreparable; the other failure mode is cavitation, which mainly occurs at the top surface or root of the blade, Blades damaged by cavitation can be repaired and reused.
2. Repair of roller shaft parts
Rolls are tools that plastically deform the (rolled) metal, and are important large-scale consumable parts that determine the efficiency of the rolling mill and the quality of the rolled material. The most common cause of roll failure is early wear failure. At present, when the roll needs to be repaired due to wear and tear, "remedial measures" such as turning or grinding are often used to correct the roll shape. The use of laser cladding to repair the surface of the roll has become a major development direction and approach to prolong the life of the roll. This technology can not only repair the roll, but also improve the wear resistance of the roll, prolong the service life of the roll, and improve the surface quality of the steel.
Usually the main reasons for the failure of shaft parts are shaft deformation, shaft fracture, and shaft surface failure. Studies have shown that the damage of shaft parts such as generator shafts and various transmission shafts is mainly caused by wear and tear. Among them, the shaft deformation and shaft fracture cannot be repaired, and the surface failure mainly caused by wear can be repaired. Using high-power laser cladding repair technology, a layer of iron-based alloy material can be laser clad on the part of the surface of the shaft parts that fails, so that the surface of the part with the clad alloy layer has good mechanical properties, and the scrapped parts can be reused.
3. Repair of molds
Molds play an important role in casting and plastic molding, and their manufacturing processes are complex, with long production cycles and high processing costs. Therefore, repairing and reusing the failed mold undoubtedly has significant economic benefits. The service life of the mold depends on the ability to resist wear and mechanical damage. Once the wear is excessive or mechanical damage, it must be repaired before it can be restored to use.
The method of laser cladding to repair the surface wear of the mold can be summarized as follows: a high-power laser beam is incident on the surface of the mold with a constant power P and a hot powder flow at the same time, part of the incident light is reflected, part of the light is absorbed, and the instantaneous After the absorbed energy exceeds a critical value, the metal melts to create a molten pool, which then rapidly solidifies to form a metallurgically bonded coating.
4. Repair of other parts
During the use of the valve, its sealing surface is in the medium for a long time and is washed and corroded by the medium. Using the laser cladding process to replace the plasma spraying and vacuum induction welding process, the NiCrBSi and CoCrW alloy coatings are clad on the sealing surface of the exhaust valve of the internal combustion engine, which not only avoids holes and micro-cracks in the coating, but also reduces the microscopic appearance of the coating. The hardness is obviously improved, and the wear resistance and corrosion resistance of the exhaust valve sealing surface are improved by 3 to 4 times.
The medium-pressure steam chamber nozzles and part of the partition nozzles of the steam turbine are seriously eroded by the steam medium. Among them, the pressure cylinder nozzle is subjected to a temperature of 350 ℃, and the material is ZG20GrMo. The average thickness of the exhaust end of the blade is only 0.02mm-0.05mm. The damaged part is repaired by general fusion welding, which is very easy to cause thermal deformation of the matrix and cracks. The laser cladding process was used for repair, and the repaired nozzle met the original design requirements, and the operation effect was good after a period of time.
The existence of the residual carburized layer on the worn tooth surface of the high-speed transmission carburized gear causes great difficulties in the repair of the tooth surface. The material of this type of gear is 20Cr2Ni4A or 18Cr2Ni4WA steel, and the depth of carburizing layer is 1.6~1.9 mm. Repaired using a laser cladding process. This cladding fully meets the requirements for gear repair. After testing, the contact fatigue characteristic life of the laser cladding layer is 15% higher than that of the carburized layer of the parts under the condition of contact stress of 2170 MPa, slip of 12.5% and No. 20 oil lubrication. This cladding fully meets the requirements for gear repair.
The flue gas expander (referred to as the hood) is an important device for waste heat power generation in industrial sectors such as oil refineries, and the roulette is the key component of the device. At present, the repair of the hood wheel is mainly using laser cladding repair. The repaired laser cladding layer is formed by layer-by-layer casting method, from the bottom layer through the middle layer to the surface layer.
