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题名: 激光快速成形同轴送粉技术的研究
其他题名: Research on Coaxial Powder Feeding Technology during Laser Rapid Shaping Processing
作者: 田凤杰
导师: 刘伟军
分类号: TG302
关键词: 激光快速成形 ; 同轴送粉技术 ; 多料仓送粉 ; 气固分离均分 ; 同轴喷嘴
索取号: TG302/T56/2010
学位专业: 机械电子工程
学位类别: 博士
答辩日期: 2010-01-27
授予单位: 中国科学院沈阳自动化研究所
学位授予地点: 中国科学院沈阳自动化研究所
作者部门: 装备制造技术研究室
中文摘要: 本文介绍了激光快速成形技术的原理和特点,分析了当前研究的热点和发展趋势。结合MPLRS的研究需要和遇到的问题,阐述了激光、金属粉末和同轴送粉三者之间的相互作用关系,进行了同轴送粉技术的研究。主要包括同轴送粉系统的研制与优化,单一粉末和多种粉末的进粉、混合和输送的理论研究和工艺参数的计算,气固分离均分理论与参数影响的仿真、优化分析,同轴喷嘴粉末喷射理论与汇聚性能的研究与仿真,同轴送粉的工艺试验分析,具体的研究内容如下: 1.为了完成准确、均匀、稳定和连续的单一或者多种粉末的进粉和输送,进行了多料仓送粉器的研究开发。落粉和进粉采用刮吸式结构,粉末输送采用载气式气力输送;采用模块化分体结构方案,对主要部件进行理论和结构的分析研究,进行了送粉量的标定与计算。针对一代送粉器的不足,进行了二代送粉器的优化升级,对主要结构部件和控制进行了改进,使送粉性能更加优良。送粉器不仅可以进行单一粉末的均质成形制造,也可以进行多种粉末功能梯度材料的成形制造。 2.为了使粉末颗粒在输送过程中保持均匀稳定的状态和进行不同粉末的良好混合,进行了粉末进粉和输送的理论研究。分别对粉末颗粒的流化粒径、临界流化速度,载气流化临界速度进行了计算与仿真;对气固两相流的在输送管内的运动状态进行分析,建立粉末颗粒的运动物理模型和数理方程,研究计算粉末颗粒群的速度变化和与载气流速、输送距离间的关系,为选取合理、经济的输送工艺参数奠定基础。  3.为了提高成形件的几何精度和组织性能,获得较高的粉末颗粒利用率,有效改善同轴喷嘴工作性能,进行了三代新型的同轴喷嘴的研制。三代喷嘴有着不同的结构和送粉形式:一代喷嘴为四层结构,采用气固两相送粉形式,由于载气在粉末流喷射汇聚过程中的发散作用,汇聚性能较差;二代喷嘴为五层结构,采用离散型送粉结构和卸载载气送粉方式,粉末流对汇聚点与激光熔池位置关系很敏感,小的变动使得成形不稳定,更适合于小激光光斑的成形制造;三代喷嘴采用环形直通道送粉结构和卸载载气的送粉形式,汇聚挺度和汇聚半径有了良好的提高,有效地改善了载气对粉末流汇聚性能的影响。建立喷射汇聚模型和数理方程并进行了仿真研究,分析不同结构参数和送粉参数对汇聚性能的影响。对喷嘴的冷却性能进行了仿真与结构优化,采用内外双层冷却的方法和等高进、出水的结构,使得改进后的冷却性能更好,提高了冷却效率。分析了在成形加工过程中激光焦点与喷粉汇聚焦点不重合对零件形状和精度的影响,提出全方位测试法可以较好地进行检测和调整。 4.为了提高流经同轴喷嘴粉末的均匀性和减小载气对粉末流汇聚的发散影响,进行了气固分离均分的研究。气固分离采用转折式惯性分离的原理,使速度较高的气固两相进入体积增大很多的分离腔,载气速度急剧减小而且方向转折,而粉末颗粒由于运动惯性和重力作用继续沿原速度方向运动,这样实现气固良好分离。粉末均分采用具有上窄下宽四个对称圆弧面的分粉锥结构,使粉末颗粒在从锥顶向锥底运动过程中沿四个圆弧面分割,实现粉末颗粒的均分。对不同结构和工艺参数条件下的气固分离、均分的进行了仿真计算,为优化改进提供指导。  5.为了测试同轴送粉系统的送粉性能,进行了实际的试验研究分析。分别检测了多料仓送粉器单一送粉和并行送粉的准确性、连续性和稳定性,不同工艺参数条件下气固两相的分离效果和粉末分割均分的状态,不同参数条件下三代同轴喷嘴粉末流喷射汇聚性能。试验发现:两代送粉器送粉的准确性、连续性和均匀性良好,而且二代送粉器相比与一代送粉器综合性能有了更好的提高;采取同时进行气固分离和粉末均分的效果要好于先均分再分离的情况;从提高成形时粉末喷射汇聚性能和同轴喷嘴的工作稳定性考虑,二代喷嘴更适合与小光斑的成形制造,三代喷嘴的汇聚性能最佳,可以满足快速成形的工艺要求;并且卸载载气可以良好提高粉末的利用率和粉末流的汇聚性能。  6.进行了单一粉末的均质成形和两种粉末的功能梯度材料成形试验分析,对成形件的形貌和内部微观组织进行了研究检测;对于单一粉末的成形试验,制得了组织均匀,性能一致,结合区域呈冶金结合的良好样件;多种粉末成形的成形件沿成形方向具有良好的功能梯度过渡,呈现出宏观组织的不均匀性和微观组织的连续性,符合FGM的结构和性能要求。不论是单一粉末的均质成形还是多种粉末的功能梯度材料的成形试验,都良好地验证了同轴送粉激光快速成形对于全方位制备组织均匀、性能一致、冶金结合或者材质渐变呈功能梯度过渡的成形零件的优越性。
英文摘要: In this dissertation, the principles and characteristics of MPLRS are introduced; the hotspots and developing trends of MPLRS technology are analyzed. For the actual demands and problems of MPLRS, the interactions among laser, metal powder and coaxial powder feeding are elaborated and the research on the coaxial powder feeding technology was made. The studies of this dissertation include coaxial powder feeding system exploration and development, study on powders feeding, mixture, delivery and processing parameters calculation; gas-powder flow separating and powder sharing technique, powders injecting and convergent characters of coaxial nozzle, the processing experiments to verify the results by MPLRS system. The specific research details are listed as following:   1. In order to complete one or several powders feeding and delivery with accuracy, uniform, stability and continuity, multi-hopper powder feeders were developed. Its powder feeding adopts scraping and absorption style, powder delivering uses pneumatic conveying and structure employs analytic structures, as well as analysis and calculation were processed in principle and structures. Used modular design ideas, main parts of feeder were analyzed and computed on principle and structure. The calibration and calculation of powder feeding were made by means of the same volume in shaping processing. According to some shortages of the primary feeder, the secondary feeder was optimized and developed. Compared with the primary feeder, there are some improvements in structure and control, and the performance of powder feeding was improved. The powder feeder can not only feed and deliver one powder to fabricate homogeneous parts but also feed multi-powder and mix, delivery to make functional graded materials parts.    2. For sake of uniform, stability state and good mixture in powder delivery processing, the principles of powder feeding and delivery were carried on. Particle size, particle critical fluidized velocity and carrier gas critical velocity were calculated and simulated. In respond to the MPLRS processing, the physical model and equation of particles motion were established and calculated, the velocity relation between powder and carrier gas was obtained, which establishes the foundation to adopt reasonable and economical delivery parameters.   3. Aimed to improve the precision, microstructure, properties of parts, acquire higher utilization ratio, enhance the working capability of coaxial nozzle, the new triple coaxial nozzles with different structure and powder style were developed. The first has four layers structure, carrier gas and particles inject together from one shrinkage annulus cavity which carrier gas makes divergence to the convergent particles. The secondary has five layers structure which injects the particles separated from carrier gas in four discrete ejection pipes. The particle convergent flow is sensitive to the laser molten pool and a small change takes a clear variation, which is better to a small laser spot. The third is the integration of the first and secondary that has one shrinkage annulus cavity to directly inject particles separated from carrier gas, which improve the particles flow convergence clearly. The models and equations were set up to analyze and simulate the injection characters by changing structure parameters and delivering parameters to research the better injecting performance. The cooling character to the nozzle of structure and simulation were conducted. The couple cooling cavities, inlet and outlet pipe with the same height cool the nozzle better. The investigation on the effect of focus position misalignment between laser beam and powder convergence on manufacturing was made and an omnidirectional detecting method to check the misalignment was brought forward and tested.   4. In order to improve the uniformity and decrease the disturbing from carrier gas flow, the gas-powder separating and sharing was investigated. Gas-powder separation uses the turnover inertia separating principle as carrier gas turnovers and its velocity decrease suddenly when the two-phase flow enter a much bigger space suddenly which makes the particles separate from carrier gas for its inertia and gravity. The particle sharing adopts powder sharing cone with four symmetric inside concaves to average the particles. The simulation of gas and powder separating and sharing was made to study the effect of different parameters.   5. The processing experiments were made to explore the reality for the coaxial powder feeding technology. Accuracy, continuity and uniformity of powder feeder were tested, as well as the gas and powder separating and sharing and coaxial nozzle with different parameters. The results show that the powder feeders have good performance with accuracy, continuity and uniformity and the secondary is better than the first. Powder separating and sharing simultaneously is better than separating then sharing.  To coaxial nozzles, the secondary is better to a small laser spot and convergent performance of the third is the best among the triple nozzles in term of working environment and stability. The separating of powder and carrier gas can improve powders utilization ration and convergent performance well.   6. Two parts—one is homogeneous materials with one powder and the other is FGM with two powders—were manufactured by utilizing the MPLRS and coaxial powder feeding system. Then the test on external pattern and internal microstructure were made. The results show that coaxial powder feeding during laser rapid shaping can fabricate not only homogeneous materials with the same characters and microstructure, but also FGM materials with gradient performance and good transition stuff.
语种: 中文
产权排序: 1
内容类型: 学位论文
URI标识: http://ir.sia.cn/handle/173321/9300
Appears in Collections:装备制造技术研究室_学位论文

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Recommended Citation:
田凤杰.激光快速成形同轴送粉技术的研究.[博士学位论文].中国科学院沈阳自动化研究所.2010
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