To improve the agglomeration of powder in a coaxial powder feeding nozzle used in the frame of a laser energy deposition technique,the influence of several parameters must be carefully assessed.In the present study th...To improve the agglomeration of powder in a coaxial powder feeding nozzle used in the frame of a laser energy deposition technique,the influence of several parameters must be carefully assessed.In the present study the problem is addressed by means of numerical simulations based on a DEM-CFD(Discrete Element Method and Discrete Element Method)coupled model.The influence of the powder flow concentration,powder flow focal length and the amount of powder at the nozzle outlet on the rate of convergence of the powder flow is considered.The role played by the nozzle outlet width,the angle between the inner and outer walls and the powder incident angle in determining the powder flow concentration is also considered.The results show that,with increasing of nozzle outlet width,the powder flow concentration per unit volume at the nozzle focal point undergoes a non-monotonic behaviour(it first increases and then decreases).When the nozzle outlet widthδis 1.00 mm,the powder flow concentration at the focal point is maximal and the powder flow convergence can be considered optimal.By increasing the angle between the inner and outer walls,the powder flow concentration related to the upper focus decreases,the focus diameter increases and the powder flow aggregation worsens.The powder flow concentration increases first and then decreases with increasing incident angle.When the incident angleθis 30°,the powder flow exhibits the best agglomeration properties.When the outlet width is smaller,the angle between the inner and outer walls is larger,and when the incident angle is set at 30°,the powder flow concentration of the coaxial nozzle can be effectively improved.展开更多
针对同轴送粉的激光定向能量沉积(DED),结合送粉方程与VOF(Volume of Fluid)方法,提出了沉积层计算模型,采用固定坐标系下的移动边界条件,对单道IN718成形过程进行了实时模拟,并进行了实验验证。结果表明:在单层单道沉积加工下,随着扫...针对同轴送粉的激光定向能量沉积(DED),结合送粉方程与VOF(Volume of Fluid)方法,提出了沉积层计算模型,采用固定坐标系下的移动边界条件,对单道IN718成形过程进行了实时模拟,并进行了实验验证。结果表明:在单层单道沉积加工下,随着扫描速度从8 mm·s^(-1)增加到14 mm·s^(-1),沉积层高度和宽度分别减小了57.1%和21.6%,计算所得沉积层高度、宽度及熔深与实验结果吻合良好。在此基础上,计算了在单向平行搭接方式下搭接率为30%的单层双道沉积层温度场分布,得到了不同搭接时刻沉积层的温度变化规律。受第一沉积层热累积的影响,熔池潜热效应会使搭接加工时的表面最高温度略低于单道加工时的表面最高温度;同时受搭接沉积层在扫描过程中高温状态的影响,第一沉积层在搭接扫描过程中会出现回温现象,回温区间为1000~1600 K,幅度为100~300 K。该研究成果对深入理解同轴送粉激光定向能量沉积工艺机理以及工艺优化具有重要意义。展开更多
基金the National Natural Science Foundation of China(Project No.51675226)Natural Science Foundation of Liaoning Province(Project No.20180550167)Key Projects of Liaoning Province(Project Nos.LJ2017ZL001,LJ2019ZL005).
文摘To improve the agglomeration of powder in a coaxial powder feeding nozzle used in the frame of a laser energy deposition technique,the influence of several parameters must be carefully assessed.In the present study the problem is addressed by means of numerical simulations based on a DEM-CFD(Discrete Element Method and Discrete Element Method)coupled model.The influence of the powder flow concentration,powder flow focal length and the amount of powder at the nozzle outlet on the rate of convergence of the powder flow is considered.The role played by the nozzle outlet width,the angle between the inner and outer walls and the powder incident angle in determining the powder flow concentration is also considered.The results show that,with increasing of nozzle outlet width,the powder flow concentration per unit volume at the nozzle focal point undergoes a non-monotonic behaviour(it first increases and then decreases).When the nozzle outlet widthδis 1.00 mm,the powder flow concentration at the focal point is maximal and the powder flow convergence can be considered optimal.By increasing the angle between the inner and outer walls,the powder flow concentration related to the upper focus decreases,the focus diameter increases and the powder flow aggregation worsens.The powder flow concentration increases first and then decreases with increasing incident angle.When the incident angleθis 30°,the powder flow exhibits the best agglomeration properties.When the outlet width is smaller,the angle between the inner and outer walls is larger,and when the incident angle is set at 30°,the powder flow concentration of the coaxial nozzle can be effectively improved.
