Simulation And Experimental Research On The Outer Flow Field Of Four-channel Coaxial Powder Feeding Nozzle For Laser Cladding

The laser cladding process is complex,the morphology and construction of the cladding layer are affected by various factors.During the transportation process,the convergence characteristics of the powder flow is affected by the flow of gas and powder,then affect the morphology of the cladding layer indirectly.In order to obtain the best process parameters for the convergence characteristics of the external flow field of the laser cladding,the velocity field,concentration field,convergence characteristics and the cladding layer of the external flow field of the nozzle are studied in depth.The laboratory four-channel coaxial powder feeding nozzle is used as the research model.Under the theory of gas-solid two-phase flow,flow model of powder particles inside and outside the nozzle is established by the FLUENT,and the elastic recovery coefficient of the particles is optimized.With the optimized elastic recovery coefficient condition,the numerical simulation analysis of the gas-powder flow under different process parameters in the laser cladding process is completed.Moreover,the observation by a high-speed camera compared with the actual cladding layer morphology,combined with the research of powder utilization rate under different process parameters,the accuracy of the model is verified.After simulating,we can find that when the carrier gas flow rate and powder feeding rate are constant,in the case of other system setting parameters unchanged,when the elastic recovery coefficient increases between 0.9 and 0.99,the powder flow speed has a little increase,and the air flow speed does not change outstanding,but the concentration and length of focus position decrease;the focus size increases.When the elastic recovery coefficient is lower than 0.9,the FLUENT residual curve has poor convergence,that is,the simulation result has a large deviation from the actual.When the elastic recovery coefficient is 0.91,the simulation effect is the best.Under this condition,the influence of different process parameters of the external flow field is simulated and analyzed,which makes the simulation results more accurate.Through the simulation of different powder feeding amounts,it is known that the larger the powder feeding amount,the higher the powder flow rate and concentration at the convergence point,but the focal length is kept at 0.015 m.When the powder feeding rate is 15g/min,the powder has good agglomeration.When the powder feeding rate exceeds 15g/min,the diameter of convergent spot gets larger.After powder convergence characteristics and single-pass laser cladding experiments,results show that the best cladding effect is achieved when the powder feeding rate is15g/min.Through the simulation of different carrier gas flow rates,the higher the carrier gas flow rate is,the higher the air velocity is.At the same time,the concentration of the convergence spot gets lower,and the focal length of the convergence spot is retained at 0.015 m.Under the condition of 4 L/min,the powder flow has better convergence.When it exceeds 4L/min,the diameter of the powder flow converging point increases.The experiment of powder convergence characteristics and single-pass laser cladding is completed.The results find that the cladding effect is the best under the condition of 4 L/min.Under the research of powder utilization rate of single-pass laser cladding during different process parameters,finding that the simulation optimization parameters 4L/min and 15g/min have the tallest powder utilization rate,reaching 73.3%-75.1%.After multiple lap cladding calculations,the latter is 74.6%-75.2%,which proves the feasibility of the simulated and optimized parameters.It has significant reference for the experimental process research.