【作者】 武强；

【导师】 左铁钏；

【作者基本信息】 北京工业大学 ， 光学工程， 2003， 硕士

【摘要】 21世纪，科学技术的发展趋向之一是向微小方向发展，由毫米级、微米级继而涉及纳米级。微米/纳米技术使人类在认识和改造自然方面进入了一个新的层次，使单位体积信息处理和运动控制的能力实现了又一次飞跃。微机械(micromachines)或者微机电系统 MEMS(micro electro mechanical systems)是80年代兴起的一个边缘性，交叉性的高技术研究领域。它是指毫米和微米尺度的机械。微机械的研究目标在于通过微型化、集成化来探索新原理、新功能的元件和系统，开辟一个新的科学技术领域和产业。美国、日本、德国等发达国家均将此项研究列为21世纪的重点发展学科。由于大功率激光器的研制成功以及商业化生产，激光快速成型技术在20世纪90年代得到了迅速的发展。在激光快速成型技术的发展中，主要出现了两个分支：一是利用快速成型的思想进行所需零件的原型制造，如立体光制造技术（SLA－Stereo Lithography Apparatus）、叠层制造技术(LOM－Laminated Object Manufacturing)、激光选区烧结技术（SLS－Selective Laser Sintering）等等；另一种技术是利用快速成型的思想进行所需零件的实体制造，获得具有使用性能的致密性功能零件。该技术也被成为直接光制造技术（Directed Light Fabrication）[9]。在微机械加工中，一个重要技术指标是分辨率。在快速成型微细加工中，把分辨率区分为扫描分辨率以及成型分辨率。成型分辨率是指成型的最小单位，也称为光固化单元；扫描分辨率则指扫描机构移动的最小距离。从成型工艺角度上讲，光固化单元就是单个激光脉冲固化固体金属粉末的体积或者单道激光光束固化金属粉末所获得固化轨迹的单位体积。要想获得细小的光固化单元，对于激光粉末快速微成形工艺而言，主要从下面两个方面入手：a）、使用具有光斑直径细小的激光器，通常选择倍频激光器或者光纤激光<WP=4>器。b）、选择粉末颗粒直径小的金属粉末作为激光粉末快速微成形固化材料。正是针对于此，北京工业大学激光工程研究院利用自身的技术优势，将激光快速成型的制造思想同微机械的研究结合起来，提出了基于纳米粉/纳米相粉进行激光快速微成形的全新思路。纳米粉/纳米相粉激光粉末快速微成形技术是激光快速成型技术在微领域的应用和发展。而实现将纳米粉/纳米相粉稳定均匀地输送至成形表面，则是利用同步送粉方式进行激光粉末快速微成形的技术前提。纳米粉/纳米相粉粉末颗粒直径小，所以具有团聚严重，吸附性强，随气相介质流动性强等特点，所以不能用传统的激光粉末快速成形送粉系统来输送，必须重新设计送粉系统。所以为了解决纳米粉/纳米相粉的稳定输出问题，本文从纳米粉/纳米相粉送粉器、粉末输送管路以及送粉工作头三个方面进行研究和探讨，最后获得均匀、稳定性好、挺度高、粉末束流形貌好的粉末输出束流。首先, 在满足工艺条件的基础上，出于能够连续稳定输送粉末束流以及获取小送粉量的考虑，改进转刷式送粉器送粉直流电机励磁电路，实现了送粉量在14/min~6909/min范围内连续可调，并且实现低送粉量下送粉器稳定运转，从而为获得较细的粉末输出束流奠定了坚实的试验基础。针对纳米粉/纳米相粉在气相介质中的传输特点，提出封闭式渐缩型粉末输送管路的思路，有效地实现了低粉末输送气体流量和减小粉末输出速度的目的，为激光粉末微成形工艺试验奠定了良好的试验前提。使用纳米TiO2粉末（平均颗粒直径为21nm）和羟基铁粉（平均颗粒直径为2.3um），通过大量粉末输出工艺试验，得出纳米粉/纳米相粉粉末输出束流形貌同粉末输出管嘴几何结构的一些定性关系，从而为下一步减小粉末输出束流直径，以及提高纳米粉/纳米相粉粉末输出束流挺度提供了有利的试验依据和理论基础。<WP=5>根据前期工艺试验设计制造送粉工作头。从试验结果看，此工作头输出粉末束流具有稳定性好、挺度高、保护气保护性能好、粉末束流无偏吹、无畸变的特点。该工作头结构紧凑、重量轻、便于安装以及精细调节。利用此送粉工作头输送超细微米羟基铁粉，使用小功率Nd:YAG激光器和倍频激光器进行简单成形工艺试验，获得了较为满意的成形效果，从而说明此送粉系统完全符合激光粉末快速微成形的工艺要求。根据激光粉末快速微成形工艺要求，设计加工了送粉工作头的精细调节装置。该装置可以实现送粉工作头倾斜角及三维位置的精细调节，从而有利地保证了粉末输出束流同激光光束焦点在成形面上的精确配合，为工艺试验打下了坚实的基础。最后使用本送粉系统结合小功率Nd:YAG连续激光器，进行简易成形工艺试验。试验证明说明该送粉系统在成形工艺中可以实现连续稳定的运行，以及说明在成形工艺中采用小送粉气体流量是有利的。更进一步说明采用纳米粉及纳米相粉这类超细粉末进行激光快速粉末微成形成形工艺这一思路的可行性。根据试验结果和激光粉末快速微成形的工艺特点，提出了一些改进措施。以上研究填补了国内在纳米粉/纳米相粉气相送粉系统研究上的空白，在国际上也处于比较前沿的研究领域。为采用同步送粉方式进行激光粉末快速微成形提供了良好的试验基础和稳定的技术保证。更多还原

【Abstract】 In the 21th century, one of the trends of scientific and technological development is the microminiaturization, and the dimension is from millimeter to micron and nanometer. The technology of micron/nanometre enables mankind to enter a new phase of understanding and remaking nature and to realize another substantial improvement in terms of the volume of information processed in given cubic unit and the ability of motion control.The micromachines and the MEMS(micro electro mechanical systems is a marginal and crossed high technology research field that rised in 20th nineties. It refers to the machines that the dimension is in the size of millimeter or micron. The purpose of research on miniature is to develop components and systems with new theories or functions through microminiaturization and integration to form a new scientific discipline and industrial sector. The developed counties, such as American, Japan and German etc, all rank this research working as the key developing subject.Due to the successful development and the commercial production of the high power lasers, the laser rapid prototyping technology developing rapid in the 20th eighties. In the process of the laser rapid prototyping, there are two main developing direction: one is using this technology to produce the prototype of the parts, such as SLA－Stereo Lithography Apparatus、LOM－Laminated Object Manufacturing and SLS－Selective Laser Sintering etc；the other is to produce the solid parts , so that people could gain the tightness functional parts that have the using characteristics. This technology is also named as Directed Light Fabrication technology.In the process of micromachines, an important technological quota is the distinguishability. In the microscopic process of rapid fabrication, the distinguishability including the scanning distinguishability and the fabrication distinguishability. The fabrication distinguishability is the min-fabrication unit, is also named as the light solidification; the scanning distinguishability is the scanning shifting mechanism’s min shifting distance.If thinking over the process of fabriction, the light solidification unit is the volume of the single laser pulse solids the metal powder, or the unit volume of the solidification trance that gained by the single track laser solidfying the mental powder. So, in the process of laser powder rapid micro-fabrication, to gain the fine light solidification unit, mainly should adopt two aspect measure:a)、using the laser that have the mini-focus spot. Usually select the doubling frequency laser or fiber laser.b)、using the micro-size particle diameter metal powder as the solidification material of the laser powder rapid micro-fabrication.<WP=7>Just taking these consideration, the NCLT of Beijing polytechnic university utilize the self technique superiority, combine the laser rapid manufacture technique and the micromachines research, put forward the innovation that using the nano/nano-phased powder as the solidification material of laser powder rapid micro-manufacture. Nano/nano-phased powder laser powder rapid mico-manufacture technique is the laser rapid formation technique’s applyment and development in the micromachines fields.If we adopt synchronous feed powder mode in the process of laser powder rapid micro-manufacturing, then the technical precondition is to feed the Nano/nano-phased powder even, steady to the formation position. Due to the Nano/nano-phased powder’s diameter is very small, it have the character that the normal micro metal powder that used in thelaser cladding don’t have. The character includes the serious agglomerating and adsorbent and easy flowing power in the flowing gas phase. So Nano/nano-phased powder conn’t be feeding with the powder feeding system used in the process of normal laser powder rapid fabrication. We must resign the powder feeding system that adapt to the laser powder rapid micao-fabrication. To resolve the Nano/nano-phased powder steady feeding project, this paper detail discuss the Nano/nan更多还原