Research On Convergence Properties Of Powders In Coaxial Laser Cladding Nozzle And The Interaction With Melt Pool

Laser cladding has always been one of most import manufacturing technologies for parts repairing and coating.In recent years,it introduces new manufacturing concepts for build-up the parts directly by laser metal deposition.The quality and efficiency of laser cladding largely depends on the powder stream characteristics in and after injection nozzle.In order to achieve the best feeding properties aiming to different application requirement,the optimization of the nozzle geometry and powder flow structure are quite necessary.In this paper,a comprehensive numerical model is developed to study the powder flow of coaxial-continuous and coaxial-discrete nozzles,which include powder stream spatial distribution,flow rate,and trajectory.The particle flux model has been solved using the computational fluid dynamics(CFD)fluent code.The study found that the divergence of powder stream at the nozzle exit is the main affect of powder spot size.By increasing the pipe length,the powder gas flow or using smaller particle size of powder can obtaine smaller powder spot size.The powder stream concentration under given nozzle and gas settings are researched by image-based technique with a high-speed camera.Calculated and measured results are well matched.Through the image capture of interaction between laser and powders by high-speed camera,the special changes of the powders under the laser irradiation were found.The change of the powder's state under different laser power and laser defocusing was explored.It was considered that the laser spot and powder influence the powder's.In this study there is a certain amount of defocus in the powder focal spot,so that the powders can be irradiated with laser light and no excessive ablation occurs.Through the simulation of the interaction between the powder and the molten pool,it is found that the powder will have a great influence on the flow of the molten pool.The molten flow from center to outward divergence is changed into a complex multi-eddy state.By using the high-speed camera the melting process of the pool area is recorded.The powder in the front part of fusion line can be melted with the movement of the molten pool.It can be more effective to reduce the surface stick powder by adjusting the process parameters to improve the size of the pool or reduce the diameter of powder...