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Design And Performance Research Of 3D Printing Powder Feeding Nozzle Based On Aerodynamics Lens

Posted on:2022-07-20Degree:MasterType:Thesis
Country:ChinaCandidate:H T LiFull Text:PDF
GTID:2518306569977399Subject:Mechanical engineering
Abstract/Summary:PDF Full Text Request
Powder feeding nozzle is an important part to realize the technology of direct energy deposition(DED).The structure of powder feeding nozzle determines the convergence effect of powder flow which affects the dimensional accuracy and mechanical properties of deposition.The traditional multi-jet or annular coaxial powder feeding nozzle has disadvantages such as being difficult to process,large divergence angle of powder stream and being unable to adjust the focus of convergence.A new type of linear focusing nozzle based on the aerodynamic lens was proposed in this paper,and the focusing performance of powder particles getting from this nozzle and the interaction between the powder stream and laser beam were also studied.Firstly,the structure of powder feeding nozzle based on aerodynamic lens was designed and the aerodynamic lens were analyzed by using a theoretical model.The influence of Stokes Number on focusing performance of particles was explored.The results show that the particles would not be focused effectively if the Stokes Number was too small,meanwhile they would diverge if the Stokes Number was too large.Then,the motion model of powder particles was established to study the powder focusing performance of aerodynamic lens.The size of the first aperture,aperture shrinkage and powder inlet angle of aerodynamic lens used in powder feeding nozzle are the main parameters that affect the focusing performance of powder particles.The motion trajectory of powder particles in the lens with different parameter combinations was simulated by using Fluent software,and the optimal parameters were determined by using orthogonal test method: the size of first aperture of the lens is 18 mm,the shrinkage of the aperture is 0.7,and the inlet angle of powder is 4.4 °.The radius of the powder stream transported by the lens is 1.61 mm and 1.55 mm at 10 mm and 20 mm outside the nozzle.The experimental results are basically consistent with the calculated results.It is found that reducing the aperture shrinkage can improve the focusing performance of powder particles.Too large powder feeding angle will lead to premature convergence of powder particles in the lens,resulting in divergence.The first aperture of lens has the least effect on the focusing performance of powder particles.Furthermore,according to the characteristics of powder feeding in the new nozzle,the distribution model of powder stream was established,and the interaction between laser beam and powder stream was studied.Based on the motion of powder particles calculated above,the spatial concentration distribution of powder particles was obtained.The reduction of laser beam by powder particles at different positions was calculated by using Lambert-Beer and Mie theories;the temperature rise of powder particles was calculated by the using the heat balance equation.For coaxial powder feeding,after optimizing the structure to shorten the length of the powder feeding nozzle itself,there is no molten particles through the nozzle,and most powder particles gather in the range of 5 mm in length and 3 mm in width.In the case of off-axis powder feeding,the effects of different feeding angles,feeding distances and feeding rates on laser beam energy reduction and distribution of powder temperature were calculated.Increasing the powder feeding angle will increase the overall temperature of the powder particles;extending the powder feeding distance and increasing the powder feeding rate will reduce the overall temperature of the powder particles,and make the powder flow more concentrated in the center of the laser spot.The laser energy distribution on the substrate surface was calculated under different powder feeding conditions.The different powder flow distribution has a great influence on the laser energy distribution in coaxial powder feeding;the laser energy on the powder feeding side is significantly lower than that on the other side,and the peak energy is reduced in off-axis feeding.Finally,the experiments of directional energy deposition were carried out by using the powder feeding nozzle based on aerodynamic lens.The results show that the deposition layer with the powder feeding angle of 70 ° is better than that with the angle of 45 ° when the nozzle is used for off-axis powder feeding.When the powder feeding angle is 70 ° and the distance is20 mm,increasing the powder feeding rate can increase the thickness of the deposition layer,and accelerating the scanning speed will narrow the deposition layer.When using this nozzle for coaxial powder feeding,directional energy deposition tests were carried out and compared with the Empower AK390 powder feeding nozzle.The deposition layers formed by using the two nozzles at a processing distance of 7,10 and 15 mm was compared.The results show that the coaxial powder feed nozzle based on aerodynamic lens can form an effective deposition layer at multiple processing heights,and has higher powder utilization and flexibility than the AK390 powder feed nozzle.
Keywords/Search Tags:Powder feeding nozzle, aerodynamic lens, performance of powder convergence, laser energy distribution, particle temperature
PDF Full Text Request
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