KrF Excimer Laser Micro-machining Mechanism And Process Experiment Of Al₂O₃ Ceramics

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.