Compared with hardening technologies such as surface spraying, carburizing, and surfacing, laser cladding technology has the characteristics of lower dilution rate, small heat-affected zone, metallurgical bonding with the base surface, relatively small distortion and deformation of the cladding parts, and easy automation of the process. At present, Huirui-Laser uses laser cladding technology to achieve pick remanufacturing in response to the problems of poor wear performance and short service life of mining picks, which greatly reduces the intensity of underground operations and improves production efficiency, which is of great significance.
1 Research progress and application of semiconductor lasers for laser cladding
1.1 The latest research progress of semiconductor lasers in China
In recent years, the research progress of high-power semiconductor lasers abroad has been very rapid. The maximum continuous output power of a single line has exceeded 600 W, and the highest electro-optical conversion efficiency is as high as 72%. A single line of 40~200 W has been commercialized. The research and development of domestic high-power semiconductor lasers has also made great progress: by widely adopting strained quantum well structure, aluminum-free active area wide waveguide large optical cavity structure and asymmetric waveguide structure in epitaxial wafer structure to improve the end face optical catastrophic damage optical power density; optimizing the cavity surface passivation coating method to greatly improve the reliability of the device; using external body grating or built-in DBR grating to achieve wavelength stability; the working wavelength has also covered the entire area from 660 nm to 2000 nm. In addition, certain progress has been made in device packaging, device reliability, beam shaping and coupling, and high-power linear array and stacked array semiconductor lasers have been successfully developed. In recent years, they have been in a state of constantly catching up with the international level.
1.2 Development and application of semiconductor lasers for laser cladding
At present, Huirui-Laser has joined hands with internationally renowned semiconductor laser manufacturers to introduce, digest and absorb their advanced semiconductor laser manufacturing technology, and creatively match semiconductor lasers with robots or various machine tools to form a laser processing system. The company has developed a 3000 W semiconductor laser processing system and has an annual production capacity of 200 sets. The processing system can run continuously for 24 hours, can adapt to complex working environments, has extremely low maintenance costs, and the remote communication detection system can provide users with expert nanny services. The specific features are as follows:
(1) High beam quality and high output power: The beam quality can reach 30 mm.mrad, and the rated output power can reach 2000~3000 W.
(2) Small size and light weight: The exclusive integrated design of power supply, main control system, and water cooling system is flexible and convenient for changing workstations at any time.
(3) High efficiency: The photoelectric conversion efficiency is more than 50%, and the output wavelength is 960~980 nm.
(4) Controllable focal length: The focal length can be designed according to user needs, and it is equipped with a red light indicator light source for easy positioning and debugging.
(5) Long working life: The bar can work continuously for 20,000 hours.
(6) Safety and stability: equipped with a safety alarm protection system; tested for impact and vibration protection before leaving the factory.
(7) Low maintenance cost and high maintenance efficiency: The bar adopts a modular design, which is easy to disassemble and assemble, and is conducive to equipment inspection and maintenance.
2 Development and application of cladding materials
2.1 Characteristics of particle-reinforced metal-based composite coating materials
Metal coating materials have good toughness and corrosion resistance, but their wear resistance cannot meet the requirements in many harsh environments; pure ceramic coating materials have high temperature resistance and wear resistance, but their toughness is relatively small, and they are prone to brittle fracture and peeling under complex loads. Particle-reinforced metal-based composite coating materials organically combine the toughness and good processability of metals with the excellent wear resistance, corrosion resistance, high temperature resistance and oxidation resistance of ceramic materials. They have the characteristics of high modulus, high strength, high thermal conductivity and electrical conductivity, low expansion coefficient, and strong high-temperature service capability. They are currently a hot spot in the research and development of wear-resistant coatings.
2.2 The latest research progress of particle-reinforced metal-based composite coating materials
2.2.1 Selection of particle-reinforced ceramics
Currently, the ceramic particle reinforcements that are widely used and studied are oxide ceramics, carbide ceramics, and nitride ceramics (as shown in Table 1), taking typical TiC and WC as examples.
TiC ceramics have low friction coefficient, high hardness and good wettability with metal matrix, which has attracted widespread attention. The latest research shows that adding Mo2C to metal ceramics can improve the wettability of bonding metal Ni to TiC.
WC ceramics have high melting point, high hardness and good stability. Its wetting angle with iron-based metal is zero, and its solubility in TiC is large, and it is easy to form TiC-WC solid solution.
2.2.2 Advanced preparation method-in-situ composite method
The wettability and interface reaction between the reinforcement and the metal matrix are the key to the preparation of particle-reinforced metal-based composite coating materials, which directly affect its performance and stability during high-temperature preparation and application. If the reinforcement (nanoparticles, whiskers, etc.) can be grown in situ from the metal matrix, the interface will have good bonding, the thermodynamic stability of the production phase will be good, and the above problems can be significantly improved. This preparation method is the in-situ composite method. The latest research reports on in-situ synthesis technologies mainly include: in-situ hot pressing technology, XD technology, CVD technology, DIMOX technology, melt impregnation technology, reaction bonding technology and SHS technology, etc.
2.3 Application of particle-reinforced metal-based composite coating materials
At present, Huirui-Laser has formed three series of powder materials: wear-resistant, corrosion-resistant and composite, including more than 40 types of nano-particle-reinforced, Co-based, Fe-based and Ni-based. Among them, the high-wear-resistant particle-reinforced metal-based composite material is developed through optimized alloy composition ratio and production process. It uses the rapid heating, high-temperature molten pool and rapid solidification thermal cycle characteristics of the high-power laser cladding process to precipitate micron-sized composite carbide particles in situ during the melting and solidification process, which are dispersed on the tough alloy matrix.
The particle density can reach 3×10⁴m㎡, forming a particle-reinforced metal-based composite laser cladding layer with excellent comprehensive properties such as wear resistance, corrosion resistance, high-temperature oxidation resistance, erosion resistance and fatigue resistance.
3 Advanced auxiliary systems
Take the auxiliary system independently developed by Huirui-Laser as an example.
3.1 Development of CNC cladding machine tools
The UHS series CNC cladding machine tools are full-function CNC cladding lathes with semi-closed loop control functions developed by Huirui-Laser based on the latest development trend of CNC laser heat treatment technology on the market. The machine tool has a wide range of uses and flexible operation. It is suitable for cladding processing of various complex-shaped parts, especially for multi-variety, small and medium-sized batches of rotation processing. It has strong process adaptability, high processing efficiency, good consistency of finished products, and can reduce the requirements for workers’ technical proficiency. The processing system can adapt to a variety of complex industrial environments and realize the real industrial application of semiconductor lasers.
3.2 Development of electric-controlled water-cooled integrated machine
Since semiconductor lasers have more stringent requirements for the working environment, especially sensitive to temperature and humidity. Huirui-Laser uses a cooling water system that can accurately control the temperature to cool its microchannels. At the same time, there is a temperature sensor and a humidity sensor at each stacking position. The sensor signal is transmitted to the control platform in real time. The signal is interlocked with the laser power switch through the control platform. A complete protection system has been established to provide the reliability of the entire 3000 W laser system.
3.3 System Integration Research
The control integration technology of the laser system, CNC lathe system, robot system and powder feeding system has been developed. Integrating multiple systems together makes its operation simpler and more convenient, further reduces the cost, and initially realizes intelligent production. Compared with the existing technology, it has the following advantages.
(1) The full digital control unit adopts the high-performance combination of FPGA+ARM.
(2) A full range of water quality monitoring and heat dissipation circuit monitoring is realized.
(3) Develop an array current source, establish a heat conduction model, realize air cooling mode, realize programmable current regulation rate, programmable overcurrent protection, overvoltage protection and other functions, and can monitor the actual driving voltage and current of the laser head in real time. It can monitor the changes in its PN connection characteristics in real time. Once an abnormality occurs, it will be shut down in time to reduce accidental damage to the laser head.
