| The gas/powder/light transmission behavior of laser cladding is very complex,which has an important influence on the heat and mass transfer of the molten pool,the formation of the cladding layer,the evolution of the structure and the mechanical properties.Depth study of the behavioral mechanisms of gas flow,oxygen diffusion,gas/powder coupling transmission and light/powder interaction is the key to realizing the adjustment and control of the cladding layer morphology and performance.In this paper,numerical simulation is used as the main supplement with relevant feasible experimental data to verify basic scientific issues such as gas flow and oxygen diffusion in protective atmosphere,gas/powder coupling transmission and light/powder interaction.The main research content and conclusions include:Firstly,aiming at the process of gas turbulence and oxygen diffusion,a coupling model of gas dynamics and oxygen diffusion is established.And the influence of nozzles,process parameters and working conditions on the flow field and oxygen concentration were systematically analyzed.The results show that for the annular nozzle,as the carrier gas channel angle,carrier gas flow rate,nozzle and substrate height increased,the molten pool oxygen concentration increased,and with the carrier gas channel gap and shielding gas flow increased,the molten pool oxygen concentration decreased.For the four-beam nozzle,with the increased of the carrier gas channel angle and carrier gas flow rate,the molten pool oxygen concentration increased,and with the increased of the shielding gas flow rate and the height of the nozzle and the substrate,the molten pool oxygen concentration decreased,and as the position of the powder feeding pipe moved out,there was no obvious change in the oxygen concentration of the molten pool.As the nozzle deflection angle increased,the oxygen concentration in the molten pool increased,and the best protection position moved in the reverse direction.The high-speed rotation of the shaft workpiece had almost no effect on the oxygen concentration of the ring nozzle molten pool.Secondly,aiming at the powder transport process,a gas/powder coupled transport model is established that is equivalent to the complex collision behavior of the powder in the nozzle,which can predict key variables such as the instantaneous position of the powder,the trajectory of the powder,and the continuous spatial average density.The influence of the gas flow rate and the state of the substrate on the above variables was also studied.The results show that the error between experiment and simulation results is less than 5 %.The morphology of the powder beams is well matched.The density of powder is proportional to the amount of powder fed.As the shielding gas flow increased,the peak powder density decreased,and the peak position moved down about 1 mm.As the carrier gas flow increased,the overall powder density decreased significantly,and the peak position moved upward by about1 mm.Before the formation of the molten pool,the workpiece rebounded to the powder significantly increasing the powder density within a height of about 4 mm from the workpiece,and the maximum increase was about 1 times.Finally,according to the light/powder interaction process,the laser energy attenuation model is established.The spatial distribution of laser attenuation energy was calculated.The influence of process parameters,the relative position of the laser and the powder beam focus on the laser energy distribution ratio were studied,and the energy distribution adjustment mechanism was discussed.The results show that the error between experiment and simulation results is less than 5 %.The percentage of laser attenuation energy has nothing to do with the power.As the amount of powder fed increased,the percentage of laser attenuation energy increased approximately proportionally.As the flow of carrier gas and shielding gas increased,the percentage of laser attenuation energy decreased,and the impact of carrier gas is greater than that of shielding gas.The laser focus is 3 mm above the focus of the powder beam,and the attenuation energy percentage reaches the peak value of about48.57 %. |
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