低密度SiO2气凝胶复合材料是近年来兴起的一种“超级隔热材料”，在航天航空及国防军工领域的热防护系统中具有重要且广阔的应用前景。然而由于其力学性能差的特点，在最终成型为热防护系统零部件的机加工过程中，会极易出现严重的加工缺陷，影响低密度SiO2气凝胶复合材料的隔热服役性能，甚至因为重大缺陷使热防护系统失效造成严重后果。因此，如何解决低密度SiO2气凝胶复合材料的加工难题，有效减少加工缺陷，提高加工表面质量，具有重要意义。本文针对低密度SiO2气凝胶复合材料难加工、加工缺陷严重的问题，从切削机理、加工表面质量评价方法、加工工艺开发及优化、典型结构件加工工艺验证等四个方面开展了系统全面的研究。首先，揭示了低密度SiO2气凝胶复合材料的切削机理。对低密度SiO2气凝胶复合材料的切削理论进行了分析及建模，阐明了低密度SiO2气凝胶复合材料的材料去除机理，总结了低密度SiO2气凝胶复合材料常见表面缺陷类型包括增强纤维裸露毛刺缺陷和SiO2气凝胶基体裂纹缺陷，解释了表面缺陷的产生机理。其次，提出了低密度SiO2气凝胶复合材料的加工表面质量评价方法。提出了分形维数和缺陷率这两个表征参数，以评价对低密度SiO2气凝胶复合材料隔热性能影响最大的毛刺缺陷和裂纹缺陷。之后，开发了低密度SiO2气凝胶复合材料的超声微锯齿直刃切割工艺、超声辅助铣削型面粗加工工艺及五轴球头砂轮超声辅助磨削型面精加工工艺，解决了低密度SiO2气凝胶复合材料二维切边和三维型面成型的加工难题，提高了加工表面质量。最后，将所开发的针对低密度SiO2气凝胶复合材料的加工工艺应用于低密度SiO2气凝胶复合材料典型结构件的加工中，成功实现了低密度SiO2气凝胶复合材料这种软脆难加工材料的复杂结构加工，验证了本文对低密度SiO2气凝胶复合材料加工工艺研究的有效性和先进性。

Low-density silica aerogel composite is a kind of “super thermal insulation material” that has emerged in recent years. It has important and broad application prospects in thermal protection systems in aerospace and national defense industries. However, due to the poor mechanical properties of low-density silica aerogel composite, in the machining process of the final molding into parts of the thermal protection system, serious processing defects will easily occur, which will affect the heat insulation service performance of the low-density silica aerogel composite, and even cause the thermal protection system to fail due to major defects. Therefore, how to solve the processing problems of low-density silica aerogel composite, effectively reduce processing defects, and improve processing quality, is of great significance.In this paper, aiming at the problems of low-density silica aerogel composite that are difficult to process and have serious processing defects, from aspects of processing mechanism, processing quality evaluation method, processing technology development and optimization, and processing verification of typical curved thin-walled structural parts, a systematic and comprehensive research has been carried out.Firstly, the cutting mechanism of low-density silica aerogel composite was revealed, the cutting theory of low-density silica aerogel composite was analyzed and modeled, and the material removal mechanism of low-density silica aerogel composite was clarified. The common surface defect types of low-density silica aerogel composite include the exposed burr defect of the reinforcing fiber and the crack defect of the silica aerogel matrix. The generation mechanism of the surface defect is explained.Secondly, a processing quality evaluation method for low-density silica aerogel composite was proposed. Two characterization parameters, fractal dimension and defect ratio, were proposed to evaluate the burr defects and crack defects that have the greatest influence on the thermal insulation performance of low-density silica aerogel composite.After that, the ultrasonic micro-serrated straight edge cutting process, ultrasonic milling surface roughing process, and five-axis ultrasonic ball grinding surface finishing process for low-density silica aerogel composite were developed to improve the quality of the processed surface in two-dimensional trimming and three-dimensional surface forming.Finally, the developed processing technology for low-density silica aerogel composite is applied to the processing of typical curved thin-walled structural parts of low-density silica aerogel composite, which verifies the validity and advancement of the research on the processing technology of low-density silica aerogel composite.