Design And Experimental Study Of Laser Cladding Powder Feeding Nozzle For Inner Hole Repair

Laser Cladding for Inner Holes is an efficient,high-quality,and environmentally friendly surface modification technology.This technology uses airflow to deliver powder particles coupled with the laser to form a metallurgical bond between the molten material and the substrate,thus completing the repair of the inner wall of hole parts.Due to the limitation of small space in the bore,the powder carrier airflow is required to transport the powder laterally during the melting process.If the airflow is small,the powder will be transported unevenly,and after increasing the carrier airflow,the powder will act on the substrate to produce a bounce phenomenon,resulting in too low powder utilization and poor melting quality.The smooth,precise,and uniform delivery of powder particles into the melt pool is essential for the repair and forming effect.In this thesis,we propose a new type of powder-feeding nozzle for the powder-feeding problem of bore laser melting and simulate and optimize its structural parameters,and then conduct powder-feeding test experiments and laser melting experiments using the nozzle,mainly including:(1)To address the powder delivery problem of bore laser cladding,an unloading type bore laser cladding powder delivery nozzle is proposed,with a three-stage structure design of an unloading section,transition section,and convergence section.The unloading section is equipped with an unloading port to divert the powder-carrying airflow that completes the lateral transport of powder,reducing the velocity of powder particles reaching the bottom of the nozzle.Based on the three-dimensional model of the nozzle,a simulation model is established by using the gas-solid two-phase flow theory to simulate and optimize the structural parameters of the convergence section and the unloading section,and analyze the influence of the parameters on the convergence of the gas-powder flow.It is found that the convergence effect of the powder flow is better when the powder feeding angle of the convergence section is 55°,the length of the powder tube is 45 mm and the diameter of the outlet is 1.2mm;and the diameter of the outlet of the discharge section is smaller than the diameter of the outlet,which can achieve the purpose of diversion of the powder-carrying airflow with less influence on the convergence of the powder flow.(2)The powder-feeding nozzle is manufactured and equipped with a complete powderfeeding system for powder-feeding test experiments to verify the performance of the optimized nozzle and to study the influence of the powder-feeding process parameters on the powderfeeding effect.The results show that the effect of different discharge port diameters on the powder feeding effect is consistent with the simulation trend,when the discharge port diameter is 0.8mm,the air-powder flow convergence is better and the powder is transported uniformly;in the carrier gas flow test experiment,it is found that increasing the carrier gas flow can improve the powder transport uniformity and air-powder flow convergence;in the powder feeding volume test experiment,it is found that as the powder feeding volume gradually increases,it will lead to insufficient conveying power and the phenomenon of uneven powder feeding.In the powder feeding volume test experiment,it was found that as the powder feeding volume gradually increased,it would lead to insufficient conveying power and uneven powder feeding,and the moderate powder feeding volume had a better powder feeding effect and could improve the powder feeding efficiency.(3)The powder feeding nozzle was mounted on the melting platform and added to the laser system to verify the effect of nozzle laser melting and forming,and applied to the solid melting of bore parts.Firstly,the effect of process parameters on the melting and forming was investigated by using an unloading nozzle to explore the key process parameters of laser power,scanning speed,powder feeding volume,and carrier gas flow rate,and to select the optimal set of process parameters;and to compare the melting effect of unloaded and unloaded powder feeding with different carrier gas flow rates.Then,the nozzle was used to conduct multi-layer cladding experiments,and the test blocks were tested for surface flaws and hardness to meet the requirements of butterfly valve seals.Finally,the workpiece was tested for repair applications using an unloading nozzle and using the preferred set of process parameters.