【作者】 祝超；

【导师】 郭东明；

【作者基本信息】 大连理工大学 ， 机械制造及其自动化， 2010， 硕士

【摘要】 核主泵是核电站的核心设备之一,并且是我国核电设备中最后一个完全依靠进口的设备。核主泵密封环的制造工艺是核主泵自主制造技术的瓶颈。陶瓷具有优异的力学、热学、化学特性,是制造密封环的常用材料。但陶瓷的极大脆性和超高硬度使传统的加工技术无能为力,而激光加工技术具有加工质量好、精度高、加工形状可以自由设定的特点,使其在硬脆材料的微细加工上优势明显。因此,陶瓷的激光微细加工技术成为解决密封环制造难题的重要途径之一。本文采用准分子激光实现Al2O3陶瓷的微细刻蚀加工。在深入分析目前陶瓷激光微细加工技术的研究现状及存在问题的基础上,对准分子激光刻蚀陶瓷的材料去除机理和加工工艺展开了较深入的研究。主要研究的内容和结论如下：(1)通过分析准分子激光光束特性和Al2O3陶瓷物理化学性质以及它们相互作用的特点,研究了刻蚀过程中发生的物理现象。针对刻蚀量随能量密度增加而下降的问题,定性分析了等离子体羽辉在刻蚀过程中的作用。通过建立热传导模型,以解析计算的方法求得了KrF激光刻蚀Al2O3陶瓷材料的刻蚀阈值。得出如下结论：(2)Al2O3陶瓷在光热和光化学作用的共同作用下得以去除,其中光热作用起主导作用。去除的材料直接以爆炸的形式汽化去除。等离子体羽辉对激光单点脉冲刻蚀陶瓷几乎没有影响。(3)根据光束发散度、稳定性和整个光束截面上能量分布三个方面的设计要求,通过分析准分子激光光束在介质中的传播规律,对光路进行了优化设计。明确了准分子激光微细加工Al2O3陶瓷试验平台搭建过程中所要注意的问题,提出了平台搭建的总体方案和光路调试方法,并对试验平台进行搭建和调试,所搭建的试验平台满足试验要求。(4)利用搭建的准分子激光微细加工平台,进行了KrF激光刻蚀Al2O3陶瓷的工艺试验。研究了刻蚀量和表面粗糙度随激光的能量密度、脉冲数、脉冲重复频率的变化规律,确定出最佳的工艺参数。(5)通过分析比较刻蚀前后的陶瓷片表面形貌可知,刻蚀孔底部均匀、平坦,而刻蚀边缘存在烧蚀痕迹。主要原因是KrF光斑能量分布不均匀,中心能量高于边缘且均匀性好于边缘,且不呈高斯分布,为近高帽形分布。这一现象与通过温度场分析预测的KrF激光刻蚀Al2O3陶瓷的结果一致,即直接以材料爆炸形式汽化去除。更多还原

【Abstract】 Nuclear main pump is one of the core equipment of nuclear power plants, and is the last device depending entirely on the imports. Seal ring manufacturing process has been the greatest bottleneck in the manufacturing technology of nuclear main pump. With excellent mechanical, thermal, chemical properties, ceramics are commonly materials used in manufacturing rings. But the great brittleness and ultrahigh hardness makes ceramics difficult machined materials for traditional processing techniques. Laser has obvious advantages in ceramics micro-machining, as its good processing quality, high accuracy and processing characteristics of the shape can be freely set. Therefore, laser micro-machining of ceramics technology is one of the key techniques to solve the sealing ring manufacturing.In this paper, we use the excimer laser to etch Al2O3 ceramics. Based on the in-depth analysis of current status and problems of laser micro-machining technology, the removal mechanism of ceramic materials and processes were researched deeply. The main contents are as follows:(1) The characteristics of mechanism of excimer laser etching were summarized. By analyzing the excimer laser beam characteristics and the physical properties of Al2O3 ceramics, the physical phenomena occurring in etching process were studied. For the problem of etching amount decreased with increase of energy density, the role of plasma plume in the etching process was analyzed qualitatively. During the etching process, both photothermy and photochemical action work in removing materials, but photothermy plays a leading role. And the ceramic materials were removed in the form of explosive vapor. The plasma plume almost has no influence on the ceramics single-pulse etching process.(2) By analysis of excimer laser beam basic characteristics, the transmission properties, the excimer laser beam propagation rule in the medium and the design requirements on the aspects of beam divergences degree, stability and energy distribution respectively, a light path optimization design is proposed. And problems presented in setting up the platform were settled. The overall scheme of the platform and optical path debugging method were proposed.(3) Using excimer laser micro-machining platform, some technological tests were carried out. And the changing rule of etching amount and surface roughness with the laser energy density, pulse number, pulse repetition frequency were studied. A set of optimum process parameters were achieved from experimental results.(4) By comparing the surface topography between original and etched ceramics, the bottom is smoother and flatter than the edge of the etching hole. The ablation trace on the edge of the etching hole showed that the energy distribution of facula was uneven. And the distribution form of the facula is not a Gaussian but a hat shapes. The phenomenon that ceramic materials were removed in the form of explosive vapor agreed well with theoretical prediction results.更多还原