飞秒激光单次扫描辅助热应力高效精密切割加工X射线望远镜超薄镜片研究

The satellite's X-ray telescope consists of thousands of ultra-thin curved glass lenses precisely. Micro damages of lenses are obtained by femtosecond laser reciprocating scanning, resulting in lenses broken in a launch of the telescope. In order to solve the problem of high efficiency and precision cutting and processing of lenses, and ensure those lenses passing the vibration test of satellite, a new method of compound machining process, which is named by femtosecond laser-assisted thermal stress lossless cleaving, is proposed in this project. The micrometer depth grooves are obtained by femtosecond laser scanning on the lenses surface, and then the heat source is used to move along the track above the lens, and the lenses is cut by thermal stress. The characteristic of the proposed method is to make full use of the synergy between femtosecond laser machining and thermal stress cutting to make up their respective shortcomings：single scan of femtosecond laser can accurately guide the crack propagation of thermal stress cutting and improve the machining accuracy; the thermal stress cleaving can make the lenses broken quickly to avoid the micro damage caused by the femtosecond laser reciprocating scanning lenses. The project will explore the thermal stress fracture mechanism of glass materials with micron grooves and the crack propagation law of curved surface cutting guided by curve trajectory. The project will explore a new approach to high efficiency and precision cutting of hard and brittle materials such as glass, and provide technical support of for the development of high energy astronomical observation in China.

卫星搭载的X射线望远镜由数千片超薄曲面玻璃镜片精密嵌套而成。飞秒激光往复多次扫描切割所得的镜片存在微损伤，在卫星发射振动测试中出现了微裂纹扩展直至破裂。为解决镜片的高效精密切割加工问题，并保证其通过卫星发射振动测试，本项目提出一种复合加工新方法——飞秒激光单次扫描辅助热应力切割。首先采用飞秒激光单次扫描镜片表面获得微米级深度的沟槽轨迹，然后采用热源在镜片上方沿此轨迹运动，通过热应力作用切割镜片。该方法特色在于发挥飞秒激光加工和热应力切割之间的协同作用弥补它们的不足：飞秒激光单次扫描可精确引导热应力切割裂纹扩展，提高加工精度；热应力作用能使镜片快速断裂，避免飞秒激光往复多次扫描镜片带来的微损伤。项目将探索具有微米级沟槽的热应力断裂机理和曲线轨迹引导下的切割裂纹扩展规律等科学问题，为玻璃等硬脆材料的高效精密切割加工拓展新途径，为我国首台X射线望远镜的自主研制奠定镜片制造技术基础。

卫星搭载的X射线望远镜由数千片超薄曲面玻璃镜片精密嵌套而成。飞秒激光往复多次扫描切割所得的镜片存在微损伤，在卫星发射振动测试中出现了微裂纹扩展直至破裂。为解决镜片的高效精密切割加工问题，并保证其通过卫星发射振动测试，项目研究飞秒激光单次扫描辅助热应力切割加工新方法。以超薄玻璃作为研究对象，分析了热应力切割过程中热阻丝对玻璃板的热传导、应力分布及裂纹产生与扩展的过程，阐明了表面具有微米级沟槽的玻璃材料热应力断裂机理。获得了玻璃的裂纹扩展模式与裂尖应力场解，并通过最大周向拉应力理论与最大能量释放率理论，解释了非对称轨迹下的热应力切割裂纹偏移现象。建立了超薄玻璃的热应力切割有限元仿真模型，利用XFEM法对具有飞秒激光轨迹引导的热应力切割在非对称路径下的裂纹扩展进行了模拟，发现飞秒激光扫描可以改善热应力切割的轨迹偏移与端口效应，揭示了曲线轨迹引导下的热应力切割裂纹扩展规律。确定了飞秒激光与热阻丝组合加工的实验路线，搭建了X射线望远镜超薄曲面玻璃镜片加工平台。在激光路径引导下完成了非对称直线和圆弧曲线的热应力切割实验，采用控制变量法求得了不同路径下合理的热应力切割参数范围，以保证切割过程不会出现缺陷且玻璃的断裂轨迹与激光路径偏离量不超过0.05mm。实现了X射线望远镜超薄曲面玻璃镜片的高效精密切割加工，镜片切割断面的粗糙度小于0.5nm。对X射线望远镜超薄曲面玻璃镜片开展了卫星发射振动试验，完成了X、Y方向最大激励幅值5g，Z方向最大激励幅值6g的振动试验，试验后检查镜片结构无破坏，使镜片通过了卫星发射振动测试。项目共发表学术论文7篇，其中SCI检索7篇，申请国家发明专利5件，毕业硕士研究生3名。项目研究成果为玻璃等硬脆材料的高效精密切割加工拓展新途径，为我国首台X射线望远镜的自主研制奠定镜片制造技术基础。