摘要
为了探讨在成形过程中沉积层结构对粉末流场的影响规律,应用气固两相流理论研究了沉积层在不断变化过程中对粉末流场浓度分布规律及粉末流汇聚焦距的变化规律,采用FLUENT软件中的离散相模型计算了粉末流场分布。计算结果表明,同轴送粉喷嘴(CPFN)的粉末汇聚浓度在径向近似服从高斯分布,与自由射流相比粉末汇聚焦点上移,粉末汇集焦距从5 mm减少到4.6 mm,上移量为0.4 mm。在沉积层宽度一定时,随沉积层高度增大,粉末汇聚点处的浓度变小,汇聚点稍微下移,汇聚特性基本不变;在沉积层高度一定时,随沉积层宽度增大,汇聚点处浓度值增大,汇聚焦点略微上移,粉末汇聚性较好。并对不同高度及宽度的沉积层进行单层沉积试验,试验结果与计算结果基本一致。说明在开环控制下制造壁厚不均且高度逐渐变化的金属零件时,由于制件结构变化而造成粉末流场变化,进而会促使沉积层高度增长的不均匀性,降低制造零件的表面成形质量。
In order to investigate the influence of parts′ structure on coaxial powder flow in the process of forming,gas-solid two-phase flow theory is considered to analyze the effect of cladding layers in the ongoing process of growth on powder flow concentration distribution and focus distance from the nozzle outlet to convergence point varying.The discrete model in FLUENT software is used to evaluate the powder flow rule.The computed results indicate that the gathering concentration of powder the coaxial powder feeding nozzle（CPFN） in radial direction approximately obey the Gaussian distribution.Compared with free jet,the convergence point of the powder moves upward and the focus distance varies from 5 mm to 4.6 mm,while the variable quantity is 0.4 mm.When the width of cladding layers is invariable,the focal point concentration in the powder flow field gets smaller,the focus distance slightly longer,and the gathering characteristic keeps almost invariant by increasing the height of cladding layers.When the height of cladding layers is invariable,the focal point concentration gets bigger,the focus distance slightly shorter,and the gathering characteristic better by increasing the width of cladding layers.The effect on the additive height of cladding layer of single trace with different widths and heights of cladding layers is carried out by experimental investigations.The numerical results are in good agreement with the experimental observations.The results indicate that the additive height of cladding layer is nonuniform of the parts with uneven thickness or gradually increasing the height during the process,which causes that the surface of cladding layers is not smooth,and then reducing the surface forming quality of cladding layers.
出处
《中国激光》
EI
CAS
CSCD
北大核心
2010年第6期1636-1642,共7页
Chinese Journal of Lasers
基金
国家自然科学基金(50675171)
国家973计划(2007CB707704)
长江学者和创新团队发展计划(PCSIRT0646)资助课题
关键词
激光技术
金属直接成型
同轴送粉喷嘴
气固两相流
数值模拟
laser technique
directly metal forming
coaxial powder feeding nozzle
gas-solid two-phase flow
numerical simulation
