基于水辅助激光裂纹修复的石英玻璃高效超精密磨削技术研究

To minimize the size of large optical systems, a large number of large aperture aspherical lenses and mirrors made of fused silica with diameter of several hundred millimeters to one meter are needed. It is rapid and cost-effective to achieve high surface quality and profile accuracy by precision grinding processes rather than lapping or polish processes. Hence, a new process，ultra-precision grinding incorporating water assisted laser irradiation of fused silica, is proposed in this research project. The subsurface damage (SSD), micro cracks under the surface, on a ground fused silica that immerged in water will be repaired by laser irradiation with carbon dioxide laser. Then, the fused silica can be ground in ductile mode as the undeformed chip thickness is smaller than the brittle-ductile transition depth of cut. The mechanisms of repairing cracks by water-assisted laser irradiaiton will be revealed by researching the coupling effect of heating and plasma shock wave. A prediction model of laser repaired depth will be built. To repair SSD on a ground fused silica and reduce residual stress introduced by laser irradiation, the process parameters of water-assisted laser irradiation wil be optimized by thermo-mechanical coupled visco-elastoplastic finite element simulation. Single and multi-cycle nanoindentation and scratch test will be conducted to study the ductile material removal mechanism of fused silica, on which SSD is repaired by water assisted laser irradiaiton. The effect of densification and residual stress on the ductile-brittle transition depth of cut will be discussed. Based on the quantitative correspondence relationship between wheel wear mechanisms and the trends of the 3D surface roughness parameters researched in this project, a dynamic quantitative evaluation model and an evaluation index system will be built and be expressed with hight and spacial 3D surface roughness parameters of wheel topography for effctive wheel wear in-situ monitoring. A 3D model of grinding wheel topography will be reconstructed based on the evaluation index system for grinding kinematics simulation. To choose the ductile mode grinding parameters for ultra-precision grinding of fused silica, the undeformed chip thickness of grinding wheel and surface roughness of ground fused silica will be calculated by grinding kinematics simulation. Finally，realize the ultra-precision composite grinding process including fine grinding, in situ water-assisted laser damage repair and ductile mode grinding. The results of this research project, which promot the development of efficient ultra-precision grinding technology of fused silica and other hard and brittle materials, have important academic significance and practical value.

为提高大口径非球面石英玻璃透镜和反射镜磨削精度、表面质量和加工效率，本项目将研究一种新的石英玻璃超精密复合磨削技术与工艺，即先采用二氧化碳激光修复浸入水中的粗磨和精磨后石英玻璃表面残留的微裂纹，再对材料进行延性域磨削。重点研究水辅助激光裂纹修复的作用机理，建立裂纹修复的理论模型；以修复裂纹、降低残余应力为目标，优化水辅助激光裂纹修复的工艺参数。通过单次和原位重复的单颗磨粒压痕和划擦试验，研究石英玻璃在激光裂纹修复后材料的延性域去除机理，建立延性域临界切削深度模型。建立基于三维表面粗糙度的砂轮磨损动态定量评价模型和评价指标体系，为砂轮磨损的原位监测提供高效的新方法。依据此评价指标体系重构砂轮地貌，通过磨削运动学仿真确定延性域磨削工艺参数，进而实现石英玻璃的高效超精密延性域磨削加工。本项目的研究成果对于促进石英玻璃等硬脆材料高效超精密磨削技术的发展具有重要的理论学术意义和实际应用价值。

为提高大口径非球面石英玻璃透镜和反射镜磨削精度、表面质量和加工效率，本项目研究了一种新的石英玻璃超精密复合磨削技术与工艺，即先采用裂纹深度可控的高效脆性域磨削方法加工石英玻璃，然后采用二氧化碳激光修复磨削后石英玻璃表面残留的微裂纹，并通过低温退火消除表面残余应力，最后再对材料进行塑性域干磨削。.重点揭示了激光修复裂纹的作用机理，以及激光辐照材料表面后的残余应力产生机理；确立了石英玻璃的高温本构方程，建立了激光辐照石英玻璃的热力耦合有限元分析模型，以修复裂纹、降低残余应力为目标，优化激光裂纹修复的工艺参数；采用低温退火去应力的方法高效地消除激光处理后的表层残余应力。研究了石英玻璃常温和高温纳米压痕和划擦的力学响应行为，分析了致密化与材料塑性流动的关系；建立了单颗磨粒划擦光学玻璃弹性应力场的解析模型，基于该模型预测了光滑无损伤的光学玻璃表面裂纹演变及脆性材料去除机理，重新划分了几种去除模式，并提出一种有效的亚表面损伤深度可控的高效精密脆性域磨削方法。为实现激光修复后的石英玻璃表面的塑性域磨削，建立了基于三维表面粗糙度的砂轮磨损动态定量评价模型和评价指标体系，依据此评价指标体系、基于实测的砂轮跳动和表面地貌重构砂轮表面状态，通过磨削运动学仿真分析了磨削工艺参数对磨粒未变形切深的影响，结合干磨削的磨削区温度场预测模型与在线温度测量，获得了优化的磨削工艺参数，实现了石英玻璃的高效塑性域超精密磨削加工。.本项目在以石英玻璃为代表的硬脆材料的脆性和塑性域去除机理方面、激光与物质相互作用机理方面、砂轮表面地貌的评价与重构方面以及磨削温度在线监测技术方面的研究成果对于促进石英玻璃等硬脆材料高效超精密磨削技术的发展具有重要的理论学术意义和实际应用价值。