As a surface modification technology of metal materials, laser cladding can effectively change the hardness, wear resistance, corrosion resistance and high temperature resistance of metal surfaces. For more than half a century, the technology has been continuously improved and developed in practical applications. In addition to materials and processes, high power laser pointer and powder feeding technologies have been continuously upgraded. In the 1980s and 1990s, cladding lasers were mainly CO2 lasers and YAG lasers. After 2010, semiconductor lasers (both direct output and fiber coupled output) appeared. In recent years, fiber lasers have begun to compete for the cladding market of semiconductor lasers.
At the same time, people are constantly exploring ways to improve the function of powder and laser, and invented a variety of powder feeding techniques, including preset powder feeding, side-by-side feeding and center feeding. The preset powder feeding adopts the powder laying or gravity powder feeder to preset the powder on the path through which the spot passes. The preset powder feeding technology is simple, the powder feeding process has no powder splash, the powder utilization rate is high, but the versatility is not strong. The side-by-side powder feeding adopts pneumatic method to send the powder into the spot, the side-by-side powder is divided into asymmetric side feeding powder and symmetric coaxial feeding powder, and the side feeding powder is easily affected by the moving direction, and the cladding quality is relatively high. difference. Coaxial powder feeding has good quality and versatility. Coaxial pneumatic powder feeding is a “powder-packing” technique that uses a multi-beam converging powder stream or a ring-shaped converging powder stream to surround the central military laser pointer beam. The center powder feeding is also a pneumatic powder feeding method. It is a kind of “optical powder coating” technology, which is designed to surround the center powder flow by designing a hollow beam.
Ultrafast lasers concentrate light energy in picosecond to femtosecond time intervals and focus light into areas of ultra-fine space that are smaller than the diameter of the hair, making the intensity of the electromagnetic field stronger than the force of the nucleus to its surrounding electrons. It is several times higher, and many other methods that do not exist on the earth can not achieve extreme physical conditions. At the same time, the laser energy is concentrated in such a short period of time, and a huge single pulse energy and a very high peak power are obtained. The high power density laser pulse can easily strip the outer electrons, and the electrons are separated from the atoms and form a plasma. .
Since the interaction time between the laser and the material is extremely short, the plasma has not been able to transmit energy to the surrounding material, and has been ablated from the surface of the material, which can largely avoid the melting of the material due to the long pulse width and low intensity astronomy laser pointer. And the continuous evaporation phenomenon (heat effect) ensures that the surrounding materials in the space range involved are not affected during the processing, and the processing quality is greatly improved. Ultrafast laser processing is therefore also referred to as “cold processing.”
In addition, the non-contact processing of the laser can avoid the problems of chipping and cracking in the traditional machine-added cutting, high precision, no micro-cracking, chipping or chipping problems, high edge crack resistance, and edge maintaining optical performance. It does not require secondary manufacturing costs such as rinsing, grinding, polishing, etc., and reduces the cost while greatly improving the workpiece yield and processing efficiency.
In recent years, high-speed laser cladding as a new laser cladding technology has attracted widespread attention in various industries such as coal mines, steel, petrochemicals, and electric power. Recently, Zhongke Zhongmei successfully used powder feeding in high-speed green laser pointer cladding technology. They used multiple lasers to wrap the center powder, and the powder melted on the molten pool and fell into the molten pool.
Compared with the coaxial pneumatic powder feeding, the central powder feeding is characterized in that the powder is a single powder flow, and there is no mutual impact scattering of the powder flow in different directions. In addition, in the vertical down-cladding process, a lower powder feed pressure can be used, so that on the one hand, the powder flow rate is relatively slow, the powder and the laser act for a long time, and the powder is more easily melted over the molten pool. On the other hand, the lower powder flow rate also reduces the ejection between the powder flow and the substrate. The practical application shows that the splash of the high-speed cladding cladding process in the center powder feeding is obviously reduced, the spark is quite gentle, and the powder utilization rate is greatly improved.
As an important part of additive manufacturing technology, laser cladding technology is a new advanced green manufacturing technology that replaces traditional surface treatment technology. The utility model utilizes a high-energy waterproof laser pointer as a heat source, simultaneously melts the high-performance powder and the base material of the part, and forms a surface cladding layer with wear resistance and corrosion resistance on the surface of the part, which not only improves the use performance of the parts, but also prolongs the service life by two. three times. Laser cladding technology is mainly used in the surface treatment of large high-value parts, especially in the surface treatment of large iron-based rotary parts. At this stage, the related technical processes have become mature for the cladding processing of the outer surface of the part, and a wide range of applications have been realized. However, the laser cladding process for the inner wall of the part, especially the inner surface of the thin-walled part, has been the bottleneck of the application of this technology.
