Optimization Design And Experiment Research Of Coaxial Powder Sending Nozzle For Laser Cladding

As one of key components of laser cladding system,coaxial powder-sending nozzle used in laser cladding has been the research hot of material providing equipment,for it can achieve the coaxial output of powder and laser beam,and has some significant advantages,such as high machining efficiency,good isotropic of cladding layer,easiness for automatic control.Aiming at the general problems of powder-sending nozzle,such as unpredicted flow morphology,poor convergence effect,and bad equality of cladding layer,the paper analyses the powder flow field,optimizes the structure of nozzle,and conducts related experimental research.Based on Eulerian two fluid model,the powder flow field analogue simulation is carried out under three dim condition,and the effect of carrier gas flux and powder sending speed on powder flow field is investigated.The result shows that after the powder flow gets out from the nozzle,it will gradually converge below the nozzle,and the concentration of powder achieves the maximum value,the diameter of powder flow achieves the minimum value in focus position.In order to get appropriate powder flow,the flux of carrier gas shouldn't be less than 9 L/min,and the rate of powder sending shouldn't be higher than 7.5 g/min.The structure parameters of the nozzle are investigated by respond surface methodology and center composite experiment design.The linear terms,quadratic terms and interaction terms which have significant impact on powder flow morphology are obtained through significance test.The mathematical models between structure parameters and powder flow morphology are established by regression fitting.In order to improve convergence effect of the powder flow,the structure of nozzle is optimized,and the optimized parameter combination is "?=62.94°,w=1.00 mm,r=5.83 mm,?=3.00° ".The powder sending experiment is carried out using the nozzle before and after optimization,and the powder concentration distribution is comparatively analysed by extracting the gray level of the photo of powder flow,the result shows that by using optimized nozzle the powder flow waist diameter declines by 39.4%,and the focus depth declines 46.4%.In addition,the simulation result got confirmed by comparing the experiment and simulation result,the total error is within 10%,which indicates the simulation result has certain accuracy.With the application of optimized coaxial powder sending nozzle in laser cladding,the single cladding layers are obtained successfully,the effects of main process parameters on geometry morphology and dilution rate of cladding layers are investigated,and a group of suitable process parameters is chose to carry out laser cladding experiment once more.The result shows that the cladding layer has good geometry morphology and appropriate dilution,which indicates that the optimized nozzle has good working performance,and could meet the requirements of laser cladding.