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1.
送粉角度对激光熔覆铁基复合涂层形状特征的影响   总被引:1,自引:0,他引:1       下载免费PDF全文
通过分析激光熔覆过程中光束、粉末和熔池间的作用机理,建立了送粉式激光熔覆材料有效利用率的数学模型,在此基础上推导了送粉角度与工艺参数之间的定量关系式,并计算了不同送粉角度下的熔覆材料有效利用率、熔高和横截面积。结果表明,在熔覆工艺参数不变的条件下,理论计算的熔覆材料有效利用率、熔覆层高度和横截面积均随送粉角度的增加而增大,且均高于实验检测值。激光熔覆过程中,由于粉末烧损和机械损失,使熔覆材料有效利用率、熔高和横截面积随送粉角度变化出现最大值,理想送粉角度为60。  相似文献   

2.
激光熔覆中金属粉末粒子与激光相互作用模型   总被引:4,自引:1,他引:3  
杨楠  杨洗陈 《光学学报》2008,29(9):1745-1750
为了对同轴激光熔覆过程中运动的金属粉末粒子的速度和温度进行理论分析,并研究各工艺参量的影响,建立了运动中金属粉末粒子的运动模型和热模型.模拟结果表明,粉嘴几何尺寸、粒子直径以及气/粉两相流初始速度是影响粒子运动行为的重要因素;粉嘴几何尺寸、激光焦点位置、激光发散角、激光功率、粒子直径以及气/粉两相流初始速度是影响粒子热行为的重要因素.在相同的工艺参量下(粉嘴出口内径r=2 mm,粉嘴倾角α=60°,初始气流速度v0=0.8 m/s),基于数字粒子图像测速(DPIV)技术,对316L不锈钢粉末粒子运动模型进行了实验验证.结果表明,运动理论模型是可靠的.该模型是掌握同轴激光熔覆过程中金属粉末粒子运动行为的有效工具;同时,热模型也是分析粉末粒子温度随不同参量变化的重要工具.  相似文献   

3.
激光熔覆中同轴粉末流温度场的数值模拟   总被引:3,自引:0,他引:3  
在激光同轴送粉熔覆中,由于激光与粉末流相互作用,粉末流整体温度分布直接影响激光熔覆的质量.基于非预混燃烧模型,将激光相处理为连续性介质,粉末颗粒相看作离散相物质,建立了激光作用下粉末流的质量、动量和能量方程.用Fluent软件进行了不同激光功率和粉末流速度条件下粉末流整体温度场数值模拟,讨论了各种参数对温度场分布的影响.为了验证该模型的准确度,利用CCD比色测温方法测量了粉末流整体温度场分布.结果表明,数值模拟与CCD检测结果具有良好的一致性,数值模拟结果对激光熔覆具有指导意义.  相似文献   

4.
 采用理想流体对称碰撞模型,分析了爆炸焊接流场中沿流线的物理变形,推导出了角变形的理论计算公式,并采用Visual C++语言对其进行了编程计算,获得了驻点近区角变形的大小及变化规律。结果表明,在驻点近区,沿来流至出流方向角变形逐步增大,其变化率在驻点附近最大;沿出流方向,给定碰撞角,角变形随来流速度的增加而增大;给定来流速度,角变形随碰撞角的增大而减小。从理论和实验方面,间接地将计算结果与前人的结论进行了对比验证,结果是一致的,以此为基础配合驻点近区的应变率场,讨论了其对爆炸焊接波状界面形成的影响。  相似文献   

5.
采用Monte Carlo程序Geant4对激光固体靶相互作用正电子产生进行了研究。研究了超热电子能量分布函数对正电子产生的影响,结果表明采用不同的分布函数,最多可致正电子产额约3倍的差异,分布函数的最大截止能量在30 MeV以上时正电子产额趋于饱和。研究了正电子产生与超热电子发散角的关联,结果表明发散角模型对正电子产额影响不大,而正电子角分布对超热电子发散角较为敏感,且靶背鞘场对正电子发散角的减小贡献巨大。模拟结果显示靶厚度的增加可导致正电子发散角的增大,而当靶厚度超过2mm时,发散角基本保持不变。此外,模拟了超热电子发散角、靶厚度及靶背鞘场对正电子电子份额比及正电子γ份额比角分布的影响。  相似文献   

6.
采用单因素法对制备球形钛粉的工艺进行研究,通过控制和调节射频等离子体工作的阳极电流与电压、中气流量、边气流量、粉体携带气流量、抽风负压和钛粉送粉速率等参数,以获得制备球形度较佳的钛粉工艺参数。通过射频感应等离子体对粒度为(17.02.0) m的钛粉球化处理研究,制备出球形度好、球化率高、表面粗糙度低的钛粉,钛粉球化率随着抽风负压增加而增加,当抽风负压大于1 800 Pa时,钛粉的球化率随着抽风负压的增大迅速降低;同样钛粉球化率也随着钛粉送粉速率增加而增加,当钛粉送粉速率大于90.0 g/min时,钛粉的球化率随着钛粉送粉速率的增大而迅速降低。  相似文献   

7.
本文对气力成栓的浓相气力输送中二次气流对输送主管的管内气固两相流动进行数值研究。考虑了二次气流的气流速度对主输送管流场的湍流扰动影响,在给出了在二次气流速度作用下,输送主管的气相场、颗粒相场的压力、速度、浓度分布的基础上;考虑了不同的二次气流对输送主管速度场的湍流扰动作用,分别给出高二次气流速度和低二次气流速度时对输送主管流场压力、气相和固相速度的扰动结果;得出二次气流速度参数对气相速度和固相速度的影响不同的结论。气流场采用修正的κ-ε湍流模型进行计算,采用相间滑移数值方法(IPSA)求解全流场的N-S方程;模拟结果与文献试验比较吻合一致。研究结果为浓相气力输送设计提供了重要的理论依据。  相似文献   

8.
高速气流中激光加热平板数值模拟与分析   总被引:1,自引:0,他引:1       下载免费PDF全文
 采用流固耦合方法,数值模拟了高速流场中激光作用下来流速度对平板温度分布的影响。结果表明:无激光辐照时,高速气流中平板有较高的气动生热平衡温度,且平板-气流之间的换热系数随来流速度增大而增大;在平板前沿换热系数增长最快,沿平板长度方向增速趋于平缓。分析了激光辐照时高速气流中激光加热平板的温度分布情况,考察了来流速度不同时,气动生热、散热和激光辐照对平板温度的影响,给出了激光辐照后的温升情况和温度分布,分析了在不同速度来流下,对流散热、摩擦生热和激光加热之间的竞争关系,结果表明,平板温度具体分布主要是加热过程竞争的结果。  相似文献   

9.
对低压涡轮后机匣进行实验研究。对不同来流马赫数及不同来流气流角下的涡轮后机匣流场参数进行测量,分析其在不同来流条件下的整流及损失情况。研究结果表明:支板叶型为前加载且按最大厚度积叠的涡轮后机匣在设计点及非设计点状态都将气流从偏离轴向偏转到基本接近轴向,且总压损失都较小。来流马赫数的改变对后机匣出口气流角影响不大,但来流马赫数的增加会导致其总压损失增加;而来流气流角改变对其出口气流角及总压损失的影响相对较小,但出口气流角及总压损失沿径向的分布会随来流气流角的改变发生变化。  相似文献   

10.
李传东  鄢雨 《光学学报》1995,15(8):91-994
从泵浦光与腔模的空间匹配函数出发,讨论了泵浦光的发散角、焦点位置等因素对激光系统效率的影响。发现在旁轴近似下,匹配函数的最大值随泉浦光发散角的增大而增大,在考虑到像散的影响后,得到泵浦光发散角的参考值。  相似文献   

11.
Laser cladding with coaxial powder feeding is one of the new processes applied to produce well bonding coating on the component to improve performance of its surface. In the process, the clad material is transported by the carrying gas through the coaxial nozzle, generating gas-powder flow. The powder feeding process in the coaxial laser cladding has important influence on the clad qualities. A 3D numerical model was developed to study the powder stream structure of a coaxial feeding nozzle. The predicted powder stream structure was well agreed with the experimental one. The validated model was used to explore the collision behavior of particles in the coaxial nozzle, as well as powder concentration distribution. It was found that the particle diameter and restitution coefficient greatly affect the velocity vector at outlet of nozzle due to the collisions, as well as the powder stream convergence characteristics below the nozzle. The results indicated a practical approach to optimize the powder stream for the coaxial laser cladding.  相似文献   

12.
The powder catchment and clad profile of the edge welding were investigated by experimental and numerical approaches in this study. The clad profile on the edges joined by a coaxial powder filler nozzle with a CO2 laser was measured and compared with the powder concentration mode, which was confirmed by powder flow visualization and numerical computations.In the numerical simulation of an impinging jet of gas-powder flow on an edge joint, the powder concentration distributed on a V groove joined by two plates was solved by FLUENT software. Based on the Gaussian mode of the powder distribution in the jet flow, a simplified mode function was proposed to estimate the clad profiles in the edge joint.Cladding experiments were performed for mild steel substrates with thicknesses of 2 and 6 mm under 1 kWCO2 laser irradiation for 304L stainless steel powder. The results show that the concave clad profiles were generated at large incline angles and the powder catchment efficiency might increase with the joint angle and substrate thickness.Based on the analytical results of the cold powder streams impinging on the edge joint, the similarity between the clad profile and the powder concentration in the edge joint is retained only at small incline angles for thin substrates. Due to the heating effects of laser beam spot and the powder re-distribution inside the edge joint, the deviation of the clad profile between the computation and experiment is increased with the incline angle and substrate thickness.  相似文献   

13.
To investigate the influencing rule of deposited layer’s shape on coaxial powder feeding flow field in the metal forming process, gas–solid two-phase flow theory is used to analyze effect of deposited layers on powder concentration distribution and variation of focus distance from nozzle outlet to convergence point (the center of the convergent zone). Different height and width parameters of deposited layers were chosen to calculate the powder concentration distribution, consequently, and also their effect on additive height of single-trace cladding layer was studied by experimental investigations. The numerical results are in good agreement with experimental observations. The results indicated that additive height of cladding layer was non-uniform under uneven wall thickness of parts fabrication condition. Consequently, the surface of deposited layers with uneven thickness is not smooth, and hence affects surface forming quality.  相似文献   

14.
葛道晗  胡州  张立强  祝世宁 《中国物理 B》2022,31(1):10701-010701
A new design of staggered array semi-packed micro gas chromatographic column was presented based on the micro electromechanical system(MEMS)technology.It was a sensor for gas sample analysis.The internal velocity fields of ten types of semi-packed micro gas chromatographic column were studied.The effects of array spacing and dislocation spacing on the flow field distribution were investigated.The results show that on the basis of ensuring the formation of virtual wall,with the increase of array spacing,the maximum velocity difference between the flow channels in the vertical direction decreases gradually,but the velocity difference in the flow channels a and b increases.When the inlet velocity was set to be 0.18 m/s,the maximum velocity difference in the channel of the staggered semi-packed micro gas chromatography column 3(CSAC3)was 0.05610 m/s.The maximum velocity difference in the channel a was 0.09160 m/s.The maximum velocity difference in the channel b was 0.02401 m/s.CSAC3 had a more uniform velocity field distribution,which can effectively suppress the laminar flow effect during chromatographic separation,and had a smaller pressure distribution,which puts forward lower requirements for carrier gas system.The staggered array semi-packed micro gas chromatography column proposed in this paper can effectively improve the velocity field distribution and pressure distribution in the channel,and provide a theoretical basis for the design of the new micro gas chromatography column structure.  相似文献   

15.
The structure below the coaxial nozzle is critical since the spatial distribution of metal powder particles determines the laser attenuation as well as catchment efficiency. It is difficult to simulate the powder concentration distribution, because the complex phenomena involved in the two-phase turbulence flow. In this paper, the air-powder flow is studied along with powder properties, nozzle geometries and shielding gas setting. A Gaussian model is established to quantitatively predict the powder stream concentration in order to facilitate coaxial nozzle design optimizations. An experimental setup is design to measure the powder concentration for this process. The simulated results are compared with the experimental results. This study shows that the powder concentration mode is influenced significantly by powder properties, nozzle geometries and shielding gas setting.  相似文献   

16.
《中国物理 B》2021,30(5):54702-054702
This paper aims at studying the influence mechanism of gas temperatures(300 K, 400 K, 500 K, and 600 K) on gas atomization by simulating the integral atomization process of the close-coupled nozzle in vacuum induction gas atomization(VIGA). The primary atomization is simulated by the volume of fluid(VOF) approach, and the second atomization is studied by the discrete phase model(DPM) combined with the instability breakage model. The results show that, at an increased gas temperature, the influences of gas–liquid contact angle and gas temperature in the recirculation zone on the primary atomization are virtually negligible. However, increasing the gas temperature will increase the gas–liquid relative velocity near the recirculation zone and decrease the melt film thickness, which are the main reasons for the reduced mass median diameter(MMD, d50) of primary atomized droplets. During the secondary atomization, increasing the gas temperature from 300 K to 600 K results in an increase in the droplet dispersion angle, which is beneficial to the formation of spherical metal powder. In addition, increasing the gas temperature, the positive effect of gas–liquid relative velocity increase on droplets refinement overweighs the negative influence of the GMR decrease, resulting in the reduced MMD and diameter distribution interval. From the analysis of the atomization mechanism, the increase in atomization efficiency caused by increasing the temperature of the atomizing gas, including primary atomization and secondary atomization, is mainly due to the increase in the gas drag force difference between the inner and outer sides of the annular liquid film.  相似文献   

17.
The effect of velocity distortions in high-speed gas flows must be allowed for in diagnostic studies using tunable lasers.We present the results of theoretical studies on the distortion of a Doppler-line profile produced by directed motion in a conical source flow. This type of flow is conviniently defined by the ratio of axial velocity at the observation station to the critical velocity and by the axial temperature. In addition, we present results for an idealized flow with constant flow velocity and temperature in the observation plane.Deviations from the Gaussian Doppler contour increase, under otherwise constant conditions, with increasing source-flow divergence angle, decreasing temperature, and increasing flow speed. Even under moderate condition (e.g. maximum semi-divergence angle of 30°, axis temperature Tl = 300 K, and axial flow speed divided by the speed of light = ql/c = 1 × 10-5), the Gaussian profile is grossly distorted because of occurrence of velocity components towards and away from the observer.Our results suggest that it will be very difficult to determine gas compositions from high-resolution spectroscopic observations (e.g. laser-absorption measurements) unless the velocity field is determined independently. Sensitivity losses in line-center and derivative spectroscopy may be estimated from our data for representative flow conditions.  相似文献   

18.
The problem of gas bubble motion in an acoustic resonator with a fluid flow is solved using numerical methods. It is shown that the distribution of the bubble concentration, which is nonuniform over the resonator length, is formed upon homogeneous introduction of bubbles. The problem on the bubble concentration distribution the along the resonator axis (with fluctuations of the bubble introduction period taken into account) is considered, and the fluctuation parameters are determined at which the periodic structure of the concentration distribution is preserved. The distribution of bubbles with different sizes over the resonator length is determined. It is shown that a resonator with a fluid flow accomplishes bubble selection by size (the average bubble concentration in the resonator increases with an increase in bubble size). The field in the resonator was calculated taking into account the effect of bubbles on sound velocity and damping.  相似文献   

19.
 以动态高压微射流振荡反应腔内部孔道流场为研究对象,建立了反应腔内部孔道的几何模型和网格模型,选择SIMPLEC算法和RNG k-ε模型,运用FLUENT软件对流场进行数值模拟,以揭示流场内各位置上的静压和速度分布。计算结果表明:高速射流撞击增加了流场内的撞击作用力,流速的急剧增加使速度梯度迅速加大,剪切应力极大增强,保证了微射流均质机极佳的作用效果;由于反应腔内部孔道流场的静压与速度变化相反,静压的急剧变化使空穴效应及压力释放效应极大增强,空穴作用力得以强化,对微射流均质机反应腔内的材料产生“腐蚀”作用。设计反应腔内部孔道时,在保证撞击区速度的前提下,应适当减小进料速度和分流管进口拐角角度,并选用较短的出料管。  相似文献   

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