Xue Yongheng, Ji Guoliang
In wind power gearbox, sliding bearings are more and more widely used in installation. By laser cladding surface modification technology, sliding bearings have been greatly improved in terms of friction, hardness, corrosion resistance and service life. However, the heat and mass transfer process in the laser cladding process cannot be observed and explored from a macroscopic perspective. Finite element method is needed to analyze the thermal cycle process in the molten pool and the solidification characteristics of the cladding layer, so as to promote the optimization of the laser cladding process parameters. Based on CuSn12Ni2 process of laser cladding on 20 steel pipes, the temperature field and flow field in the cladding process are simulated in this paper. A finite element model of the flow field considering the fluid flow in the molten pool is established, and the flow of the molten pool is simulated in the form of dynamic grid. The fluid flow rules in the molten pool under different process parameters were investigated. When considering the fluid flow in the molten pool, with the increase of cladding time, the flow field distribution tends to be stable after 0.4 s, and the fluid velocity remains at 0.00129 m/s. With the increase of laser power and the decrease of scanning speed, the heat absorbed inside the molten pool increases, which makes the convection in the molten pool strengthen, and the surface size will increase. Finally, the solidification mode of CuSn12Ni2 alloy cladding layer and the microstructure transformation characteristics of heat-affected zone of 20 steel tube matrix were investigated, and the simulation results were verified. According to the calculation of G and R of the cladding layer, the G/R value of zone A at the bottom of the cladding layer is higher, which is 24.6e9 k·s·mm^-2, showing plane crystallization. The G/R value in zone C at the top of the molten pool is 0.59e9 k·s·mm^-2, showing the coexistence of isotropic crystals and columnar dendritic crystals. The B zone in the middle of the pool with the lowest G/R value (0.06e9 k·s·mm^-2and the highest G×R value (4210.71k·s^-1) shows columnar dendritic crystals. It is found that the calculated results of G/R and G×R are in good agreement with the experimental solidification model, which verifies the correctness of the model.
Laser Cladding; Sliding Bearing; Flow Field; Numerical Modeling