Flow Characteristics Of TC4 Powder Transported By Laser Cladding Carrier Gas

Laser cladding is an advanced technology for improving and optimizing the surface of workpieces,which has many advantages such as high strength,high corrosion resistance,low cost and arbitrary choice of powder.The powder feeder is responsible for transporting the powder and ensuring a continuous and stable powder flow;the powder flows evenly in the powder feeder and then enters the powder feeder;the powder feeder ensures that the powder is accurately and stably fed into the laser light source.A stable powder delivery process can ensure the quality of the process,but in practical engineering applications there are often problems such as unstable powder delivery,uneven powder delivery and blocked pipes due to the structure of the pipeline and the different properties of the powder itself,as well as insufficient air flow,making it difficult to ensure efficient and stable delivery.However,the current research on laser cladding mainly focuses on the powder convergence,utilisation rate and actual cladding effect at the powder feeding nozzle,and such research is carried out under the assumption of uniform and stable powder delivery.In this thesis,the flow characteristics of TC4 titanium alloy in tube conveying are analysed to compare the velocity,concentration distribution and powder discharge under different parameters,and to select the optimal parameters to provide theoretical support for the pipeline design and conveying parameters in the gas-carrying system:(1)In view of the inability of conventional simulation methods to achieve powder collision and powder quality statistics,a coupled computational fluid dynamics and discrete unit method(CFD-DEM)approach was used to numerically simulate TC4 powder transport.Due to the excessive modulus of elasticity of the TC4 powder severely prolonging the simulation time,in order to improve the efficiency of the calculation,the modulus of elasticity was reduced by a factor of 100 and the effect on the transport results before and after the reduction was analysed,showing that there was no significant difference in the powder flow state and the change in kinetic energy.(2)To address the problem of unstable powder delivery(powder wheezing)in TC4 powder carrier gas conveying process due to different piping structures,the piping structure was designed according to the actual piping arrangement of the laser cladding equipment,and TC4 powder with a particle size of 100 μm was simulated for conveying.The results show that the unstable powder delivery is caused by the collision of particles in the bend section and the real time change of speed,compare the flow state of powder under different piping structure,optimize the piping structure,then build the same test platform as the simulated piping structure,and compare the actual measurement of powder volume change with the simulation results,and find that the overall trend is basically consistent.(3)To investigate the influence of air flow rate on powder flow characteristics,the results show that the increase of air flow rate can significantly improve the stability of powder feeding,but when the air flow rate is greater than 6L/MIN,the powder will form a longer particle bundle after flowing out of the bend tube,and the powder will be distributed more loosely in the tube after the particle bundle is completely diffused.After the powder is completely diffused,the powder is distributed more loosely in the tube,which is not conducive to the uniform transport of powder.(4)To address the problem that particle size can also cause unstable powder delivery,three different particle size distributions of small(25-50μm),medium(65-150μm)and large(150-270μm)particle groups were set up to investigate the effect of particle size on powder flow characteristics and to compare with a single particle size.The results show that the particle groups with particle size distribution and single particle size have the same overall distribution,but there is a certain concentration difference due to the size of the particles themselves;the three different particle size distributions form different flow patterns in the vertical section and the bend section,and the relationship between particle velocity and particle size is obtained,and as the flow pattern changes and the particle size increases,the overall conveying process gradually becomes unstable,and finally The maximum error of powder delivery per unit time was 4.61%,13.3% and 10.4% for TC4 powder with small,medium and large particle size distributions respectively,and the simulation results were relatively reliable.