| Due to the high efficiency and good quality of the coating,the ultra-high-speed laser cladding technology has great application prospects in the electroplating industry,surface coating field,and laser additive manufacturing.In this paper,the theoretical model of coaxial powder flow feild of laser cladding and particle thermal field has been analized,and a comprehensive model has been presented,which is based on unsteady-tracking technology.Using this model,the question about energy attenuation as well as powder temperature field under different process parameters have been studied.And experiments and analysis have been performed for energy attenuation and ultra-high-speed laser cladding process.The research contents are as follows:(1)The basic principle of the coaxial laser cladding process has been analyzed,and the theoretical model of the process has been established.By using FLUENT and unsteady-tracking technology,the CFD models of conventional four radially symmetrical powder flow nozzles and ultra-high-speed powder flow nozzle has been established and studied.Through simulation results,it has been found that the ultra-high-speed powder flow nozzle can form a powder spot with a radius of 0.8 mm,the powder concentration is highest in the space of 15 mm to 19 mm below the nozzle,when the conventional nozzles can only form a powder spots with a radius of 2.3mm,and the zone is in the space of 14 ? 15 mm below the nozzle.And the feasibility of the model was verified by through experiments.(2)A energy attenuation algorithm based on powder shading ratio has been designed.The attenuation under different parameters can be quikly obtained by using FLUENT unsteadytracking results and MATLAB program.The energy attenuation law of laser passing through powder flow has been analyzed by this algorithm.After analyzing the atenuation amount under different parameters,it has been found that the ultra-high-speed powder flow nozzle generate more than 50% attenuation of laser energy,while the conventional coaxial nozzle is only 20%.The effectiveness of the algorithm is verified by experiments.It is also found that the energy attenuation of the laser passing through the powder flow has a Gaussian function.(3)The laser heat source model has been modified and the powder temperature field calculation model based on unsteady-tracking technology has been established.The powder temperature field under different process parametershas been studied by using the model.It was found that the powder spot temperature can be increased by increasing the laser power and powder defocusing.The small particle size and the increased mass flow rate as well as the carrier gas flow rate can improve the utilization rate of the laser energy in the powder cloud.And it has been predicted that when the powder defocus amount is 2mm,the laser power is4 k W,the powder feed amount is 21 g / min,and the powder particle size is 30 um,the laser scanning speed can reach 10 m / min.(4)The structure and characteristics of the 4k W ultra-high-speed laser cladding system has been analyzed in detail.And the cladding test was carried out using this ultra-high-speed cladding system to study the effects of laser power,powder feed and air supply on the formation of the cladding layer.It's found that the thickness of the cladding layer has a large increase with the increase of power,mass flow rate and carrier gas flow rate,and the width of the cladding layer increases with the power but decreases slightly as the mass flow rate and carrier gas flow rate increases. |
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