| With the development of science and technology,a new manufacturing technology has been on the stage of history-laser cladding value-added manufacturing technology,which subverts the traditional manufacturing concept.As a key component of the implementation of this technology,coaxial powder feed nozzles play a vital role in the precision and quality of laser cladding remanufactured parts.It has many adantages,for example,the powder particles carried by the carrier gas are uniformly dispersed in the circumferential direction inside the nozzle,and the annular shrinkage uniform powder curtain is coaxially outputted from the nozzle outlet and the laser beam.Besides,the material utilization rate is high and the cladding layer is isotropic.it is very important to improve manufacturing precision and quality in the research of cladding equipment based on these advantages.In this paper,the design optimization of the structure,the flow field simulation analysis of the powder particles in the nozzle and the powder feeding experiment are studied aimed at the problems that the coaxial powder feeding nozzle powder has uneven circumferential dispersion,poor convergence effect,and structural design defects cause powder blocking.(1)Based on the theory of fluid mechanics,pneumatic conveying and gas-solid two-phase flow,the fluidized,stressed and moving state of the powder particles in the pipeline is analyzed.and the transport speed of the powder particles in the pipeline and the reaction time to the nozzle are analyzed.(2)The geometric model and concentration distribution model of powder flow convergence of coaxial nozzle were established,and the influence law of nozzle structure parameters on powder aggregation morphology and concentration distribution law were analyzed by using the theoretical model,so as to provide theoretical basis for the optimization of nozzle structure parameters.The temperature rise model of powder particles interacting with laser before falling into the molten pool was established,which showed that the smaller the nozzle cone Angle,the longer the interaction time between powder particles and laser,the higher the temperature,and the closer to the center of laser beam,the faster the particle temperature increased.(3)Aiming at the problems of the existing nozzle,such as inhomogeneity of circumaxial powder dispersion,poor convergence and powder blocking,a nozzle structure was designed to solve the problems of centrifugal force,elastic collision with wall surface and powder blocking caused by the existing nozzle structure.Fluent gas-solid two-phase flow discrete phase flow channel simulation is carried out on the designed nozzle structure,and the influence of nozzle structure parameters on powder convergence is simulated to determine the approximate range of structural parameters optimization:the powder cavity inclination angle is between 18° and 26°,and the exit gap is between 0.5-1mm.(4)The response surface regression analysis is used to fit the mathematical model of the three outlet structural parameters of the nozzle,the focus point of the powder sink and the waist beam radius at the focal point.The mathematical model is used to optimize the multi-objective.For the target value powder convergence,the optimal combination of nozzle structures is:r=5mm,w=0.5mm,?=20.76°,when the focal length f2=14mm and the lower focal radius r2=1.5mm.Through simulation and comparison,the results show that the circumferential dispersion uniformity and convergence of powder of the optimized nozzle are better than that of the original nozzle.The radius of powder convergence focus is 1.5mm,which is consistent with the optimization results and the concentration is twice as high as that of the original nozzle.(5)The optimized nozzle was used for powder feeding test,and the results showed that the powder dispersed evenly in the circumferential direction,and the powder feeding effect was greatly improved compared with the original nozzle.Finally,the single-channel cladding test was carried out to study the influence of process parameters on the cross-section morphological characteristics of nozzle cladding layer and analyze its performance. |
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