【正文】 etal concentration will reach the maximum kg/m3 when it is 5 mm under the bottom of the nozzle. Energy, momentum, and mass transmission process exist in coaxial powder feeding system, which directly determines the size, precision and performance of the part made by LMDM. Thus, it is necessary to conduct some research on its powder flow field, but until now, there is only limited relevant research on this subject [14, 15]. 沈陽理工大學(xué)學(xué)士學(xué) 位論文 37 Fig. 1 Working principle of the coaxial powder nozzle, α is the anglebetween fed powder and the horizon, β is the angle between shield gasand the horizon In the discrete phase model in this paper, the gas phase is puted by the standard k–ε turbulent flow model, and the discrete phase is puted by building particle track model. There are assumptions as below in the model: (1) the particle’s movement is steady, and the powder and gas have the same velocity。 時，粉末匯聚的速度矢量圖 沈陽理工大學(xué)學(xué)士學(xué) 位論文 30 圖 70176。由此可見，當(dāng)保護(hù)氣進(jìn)口速度為 ，粉末的匯聚性能較好。 圖 氣腔和粉腔錐角角度均為 60176。 、進(jìn)口速度為 2m/s，氣腔的錐角角度為 90176。 （ 11）兩相流，包括帶空穴流動計(jì)算。 （ 5）過濾器 —— 或者叫翻譯器，可以將其他 CAD/CAE軟件生成的網(wǎng)格文件變成能被FLUENT識別的網(wǎng)格文件。 式 ()到 ()為 NavierStokes 方程。 （ 6）電磁振動送粉器：是基于機(jī)械力學(xué)和氣體動力學(xué)原理工作的，反應(yīng)靈敏，由于是用氣體做為載流體將粉末輸出，所以對粉末的干燥程度要求高，微濕粉末會造成送粉的重復(fù)性差。這些設(shè)備都是多種技術(shù)的集成，主要是為了提高快速成型制造制作精度和可靠性，涉及工藝原理、工藝方法、溫度控制、激光及冷卻系統(tǒng)、精密機(jī)械傳動等硬軟件方面。 5 匯聚過程的計(jì)算結(jié)果與分析 ................................................................................................. 17 同軸送粉的匯聚效果的總體分析 ..................................................................................... 17 粉氣同角時匯聚特性數(shù)值模擬 ................................................................................. 17 兩腔錐角變化對匯聚性能影響 ............................................................................... 17 氣腔進(jìn)口速度對匯聚性能影響 ............................................................................... 21 粉氣非同角時匯聚特性數(shù)值模擬 .............................................................................. 24 氣腔進(jìn)口速度對匯聚性能影響 .............................................................................. 24 粉腔錐角變化的匯聚性能比較 ............................................................................... 27 致 謝 .............................................................................................................. 錯誤 !未定義書簽。 質(zhì)量守恒定律 ....................................................................... 錯誤 !未定義書簽。 送粉技術(shù)現(xiàn)狀及存在的問題 ............................................................. 錯誤 !未定義書簽。 同軸送粉模擬計(jì)算前處理 ................................................................ 錯誤 !未定義書簽。在 Austin 舉行的 2021 年度快速成型制造年會上，許多大學(xué)和公司都推出了各自的成型系統(tǒng)。 （ 4）毛細(xì)管送粉器：這種送粉器能輸送的粉末直徑大于 。 流體力學(xué)基本方程 流體在流動過程中遵循機(jī)械運(yùn)動的普遍規(guī)律 :質(zhì)量守恒定律、動量守恒定律和能量守恒定律，由此可導(dǎo)出流體力學(xué)最基本的連續(xù)方程、動量守恒方程（ NavierStokes 方程）和能量守恒方程。而 LISP 類型的語言允許高級用戶通過編制自定義函數(shù)改變軟件的外觀，使用戶在使用中可以根據(jù)自己的喜好定沈陽理工大學(xué)學(xué)士學(xué) 位論文 12 制界面，這點(diǎn)是 FLUENT 軟件的一個顯著特色。 （ 6）化學(xué)組元混合與反應(yīng)計(jì)算，包括燃燒模型和表面凝結(jié)反應(yīng)模型。 、 70176。 粉氣同角時匯聚特性數(shù)值模擬 兩腔錐角變化對匯聚性能影響 以下是兩腔的錐角角度同為 60176。 時，粉末的匯聚性能較好。 ，粉末的匯聚性能模擬結(jié)果見圖 。 最后，向在百忙中抽出時間對本文進(jìn)行評審并提出寶貴意見的各位專家表示衷心地感謝！ 新的生活即將開始，前進(jìn)的號角已經(jīng)吹響，我會繼續(xù)努力地學(xué)習(xí)，生活和工作，以期用自己的微薄之力來回報(bào)母校的培育之情，并為社會的進(jìn)步做出新的貢獻(xiàn)！ 參考文獻(xiàn) ,胡國清 ,劉文艷 ,林忠華 .快速原型研究綜述 [J].廈門大學(xué)機(jī)電系 .2021 ,巨麗 ,杜詩文 .快速原型制造技術(shù)與進(jìn)展 [J].太原重型機(jī)械學(xué)院學(xué)報(bào) ,2021:255258 .快速成型 先進(jìn)的 現(xiàn)代制造技術(shù) [J].《鑄造技術(shù)》 .1999,4:3739 4. 王秀峰等 . 快速原型制造技術(shù) .中國輕工業(yè)出版社， 2021 5. 胡曉冬等 . 金屬直接成型技術(shù)的發(fā)展與展望 .工具技術(shù)， 2021（ 10）： 36 沈陽理工大學(xué)學(xué)士學(xué) 位論文 34 6. 王從軍等 . SLS 成型件的精度分析 [J]. 華中科技大學(xué)學(xué)報(bào)， 2021（ 6）： 7779 附 錄 英文文獻(xiàn) Numerical simulation of powder flow field on coaxial powder 沈陽理工大學(xué)學(xué)士學(xué) 位論文 35 nozzle in laser metal direct manufacturing Anfeng Zhang amp。 subscripts i and j are just subscripts for the velocity ponents and the space coordinates. According to Launder’s remended numerical value and the experimental validation, where σk=, s 1:3, C1=, C2= , Cu= 0:09. Discrete phase track putation equation In FLUENT software, the track of a dispersed phase particle is solved by the force balance on the particle in a Lagrangian reference frame (following the particle coordination). The force balance equates the particle inertia with the force acting on the particle, and can be written as Where u is the pressive gas velocity, up is the particle’s velocity, gx is the acceleration of gravity at x direction. FD is the drag force per mass for powder, ρP is the density of powder, Fx is other forces in the calculation process. In Eq. 3, it loses sight of thermal force (when considering heat transfer), Brown force (to deal with the particle of inferior microcosmic size), Saffman force (to deal with the particle of inferior microcosmic size), the inertia (the additional quality force is caused by the flow field around the particles accelerating) and the gravity [8]. 3 Numerical putation of flow field in and out of the nozzle Discrete model and grid selections The multiphase behavior of the discrete model is simulated by FLUENT. Particle phase will be treated as discrete phase if its volume percentage of granule phase is less than 10%. 沈陽理工大學(xué)學(xué)士學(xué) 位論文 39 Otherwise, the particle phase will be treated as fluid. In this discrete model, the gas track, the velocity and concentration field in and out of the powder field are puted. According to focus principle and columniform putation area of the nozzle, a 2D axisymmetric model is built up, of which the putation area size is 25 mm55 mm, the inner cone angle is α and the outer cone angle is β. The putation area of the nozzle is shown in Fig. 2. As different structure of the nozzle can result in different concentration field of the powder, the distribution of powder’s concentration is studied corresponding to different cone ring gap (H=1 mm, mm, 2 mm) and different inner and outer cone angle(α, β= 45176。 σk and σs are respectively the turbulen