Analysis Of Agglomeration Law Of Powder Flow In Laser Additive Remanufacturing Nozzle

As an emerging technology in recent years,laser additive remanufacturing technology has been widely concerned and applied in various fields.Its gas powder flow field characteristics are an important factor affecting the forming quality and forming efficiency of parts.In this paper,based on the theory of gas-solid two-phase flow theory,coupled with EDEM-FLUENT software for coupling simulation,we explored the influence of various factors on the flow field of laser additive remanufacturing coaxial powder feeding powder.By introducing focal position,focal diameter,radial powder distribution volume fraction,axial powder distribution volume fraction,unit distance powder flow volume volume fraction,focus center position offset,the number of particles in the effective processing range,etc.Numerical simulation analysis of the flow field of coaxial powder feeding in additive remanufacturing.At the same time,the same powder feeding process parameters are used to verify the experiment,and the calculation error rate is guaranteed to be below 25%,indicating that the DEM-CFD coupling method is used to simulate the nozzle powder flow field with high accuracy and certain guidance.Through the DEM-CFD coupling method,the influence of nozzle position and attitude on powder flow field volume fraction was studied.The results show that with the increase of the distance between the nozzle and the substrate,the turbulence phenomenon of the airflow field is significantly reduced,and the number of particles reflected into the central optical path is significantly reduced.When the processing height is near the lower focal height,the powder flow field has a better Convergence effect,and has higher particle volume fraction;As the processing angle of the nozzle increases,the longer the time required to form a continuous and stable mass flow,the mass flow tends to become smaller,the overall offset of the powder flow field increases,and the mass flow of the particles decreases within the effective processing range The situation is remarkable,and the focus is not obvious.The DEM-CFD coupling method was used to study the influence of the substrate shape on the gas-powder flow field.The results show that in the process of the nozzle center axis away from the boundary,the turbulence phenomenon of the air flow field at the wall contact portion increases,the low-speed area of the sidewall decreases,the negative pressure range decreases,and the number of particles in the effective processing range shows a decreasing trend;As the width of the thin-walled substrate increases,the airflow field range develops significantly on both sides,the volume fraction of the processing center gradually decreases,the effective processing range of particle flow increases first and then maintains stability,and the particle radial range always increases;In the process of arc surface substrate processing,as the curvature of the arc surface increases,the number of particles in the effective processing range decreases,the particle volume fraction at the processing point continues to increase,and the particle aggregation effect during the processing of the convex substrate is significantly higher than the concave surface Materials,convex substrates have a good air flow field,concave substrates will form a larger turbulence range and affect processing.The forming effect of convex substrates is significantly better than concave substrates.The DEM-CFD coupling method was used to study the influence of lateral wind velocity on the gas-powder flow field.The results show that the crosswind has a greater influence on the free jet.With the increase of the crosswind speed,the overall drift of the airflow field is obvious,and the phenomenon of particles overflowing the airflow field will occur,so that the protective gas will lose its protective effect;the impact jet has a small processing height,The air velocity at the outer boundary of the coaxial jet zone is high,and the effect of crosswinds on it is small.However,the presence of crosswinds will affect the range of the wall jet zone and the low velocity cone of the mixed impact zone,although the highest volume fraction point is affected by crosswinds.It is small,but the overall deviation of the particles on the substrate surface will change the effect of laser cladding to a certain extent.The DEM-CFD coupling method was used to study the influence of powder morphology on gas-powder flow field.The results show that under the same particle mass flow rate,the smaller the particle size,the higher the dispersion.As the particle size increases,the upper focus position gradually moves down,the volume fraction gradually decreases,and the upper focus diameter gradually increases;the lower focus position.There is also a downward trend,with the volume fraction increasing first and then decreasing,and the lower focal point diameter decreasing first and then increasing.The aggregation effect of particles with a particle size between 90 and 120 μm is excellent.As the mass content of near-spherical particles increases,the position of the lower focal point moves down,the radial and axial volume fractions of the lower focal point decrease,and the focal diameter does not change significantly.As the material density increases,the length of focal region increases,the upper focus moves up,the agglomeration of powder flows weakens,and the lower focus moves down,the agglomeration of powder flows strengthens.The paper has 122 figures,18 tables and 69 references.