BK7光学玻璃超声振动磨削亚表面损伤的研究

发布时间：2018-05-12 06:56

本文选题：光学玻璃 + 超声振动磨削　；参考：《哈尔滨工业大学》2017年硕士论文

【摘要】：光学玻璃具有稳定的物理、化学性能及高度光学均匀性,因此广泛应用于相关工程领域,但其高脆性、低断裂韧性的特点降低了光学玻璃的可加工性能,传统磨削技术极易在已加工的亚表面引入各类损伤,对加工质量及效率等都产生不利影响。降低加工零件亚表面损伤程度,有助于减少零件后续研抛时间,提高零件的整体加工效率。超声振动辅助磨削加工技术具有降低平均切削力、减少加工微裂纹、提高材料去除率等优势。但目前超声振动作用对光学玻璃亚表面微裂纹扩展的影响尚未明确,对超声振动作用下光学玻璃亚表面损伤形成及预测的研究还不完善。因此开展超声振动磨削中光学玻璃亚表面损伤的研究对实现该类材料精密低损伤加工具有重要理论意义和实用价值。超声振动作用对光学玻璃材料亚表面微裂纹扩展的影响分析是亚表面加工损伤研究的基础。本文分析了超声振动效应对单颗磨粒运动轨迹及动力学特征的影响。通过准静态印压实验,建立了BK7光学玻璃在准静态载荷作用下的内部应力场分布模型,分析了应力场驱动下微裂纹成核与扩展机制,结果表明,磨粒运动轨迹重叠及超声效应的引入造成的中位裂纹屏蔽作用是使裂纹扩展深度出现下降的主要原因。通过超声振动辅助旋转刻划实验,分析了冲击载荷对光学玻璃材料脆性断裂过程的影响,结果表明由于磨粒惯性冲击力的作用,使得BK7光学玻璃材料动态力学性能发生变化,内部裂纹更容易成核,微裂纹闭合导致的材料脆性断裂成为材料去除的主要原因。上述研究为后续光学玻璃超声振动磨削亚表面损伤规律和预测的研究提供理论基础。超声振动磨削加工中砂轮多磨粒作用和高频振动效应都会对亚表面损伤产生重要影响。本文进行了超声振动磨削加工实验,采用扫描电子显微镜对光学玻璃加工亚表面裂纹微观形貌进行了检测,分析了多磨粒、多种载荷作用下亚表面裂纹损伤的特征及其形成机制,结果表明,磨粒加载方向及材料动态性能变化是造成BK7玻璃亚表面裂纹形态变化的原因。在此基础上,通过实验研究获得了磨削加工参数及砂轮参数对亚表面裂纹最大深度的影响规律,为后续亚表面裂纹最大深度预测模型的建立提供依据。对亚表面裂纹最大深度实现有效的预测是减少零件后续研磨和抛光时长、提高加工效率、改善磨削加工质量的关键。根据前述分析结论和研究,本文分别采用最小二乘支持向量机及高斯过程回归方法建立了超声振动磨削加工BK7光学玻璃的亚表面裂纹最大深度预测模型,在此基础上,通过磨削加工实验对两种预测模型的有效性进行了验证,并对预测精度进行了比较。为实现光学玻璃材料超声振动磨削加工工艺参数的优选提供了基础和依据。
[Abstract]:Optical glass has stable physical and chemical properties and high optical uniformity, so it is widely used in related engineering fields, but its high brittleness and low fracture toughness reduce the processability of optical glass. Traditional grinding technology is easy to introduce various kinds of damage to the machined subsurface, which has adverse effects on the quality and efficiency of machining. Reducing the degree of sub-surface damage of machining parts is helpful to reduce the time of subsequent polishing and improve the overall machining efficiency of the parts. The ultrasonic vibration assisted grinding technology has the advantages of reducing the average cutting force, reducing the machining microcracks and improving the material removal rate. However, the effect of ultrasonic vibration on the crack propagation of optical glass subsurface is not clear, and the research on the formation and prediction of subsurface damage of optical glass under ultrasonic vibration is not perfect. Therefore, it is of great theoretical significance and practical value to study the subsurface damage of optical glass in ultrasonic vibration grinding. The analysis of the effect of ultrasonic vibration on the crack propagation of optical glass is the basis of the research on the damage of subsurface processing. In this paper, the effect of ultrasonic vibration on the motion trajectory and dynamic characteristics of a single abrasive particle is analyzed. The internal stress field distribution model of BK7 optical glass under quasi-static loading is established by quasi-static stamping experiment. The mechanism of microcrack nucleation and propagation is analyzed. The main reasons for the decrease of crack propagation depth are the overlap of the motion trajectories of abrasive particles and the median crack shielding caused by the introduction of ultrasonic effect. The effect of impact load on brittle fracture process of optical glass material is analyzed by ultrasonic vibration assisted rotating characterization experiment. The results show that the dynamic mechanical properties of BK7 optical glass material are changed due to the effect of inertia impact force of abrasive particles. The internal crack is easier to nucleate, and the brittle fracture caused by micro-crack closure is the main reason for material removal. The above research provides a theoretical basis for the study of the subsurface damage and prediction of ultrasonic vibration grinding of optical glass. In ultrasonic vibration grinding, the effects of multi-abrasive and high-frequency vibration on the subsurface damage are very important. In this paper, ultrasonic vibration grinding experiments were carried out, and the micro-morphology of sub-surface cracks in optical glass processing was detected by scanning electron microscope (SEM), and the multi-abrasive particles were analyzed. The characteristics of subsurface crack damage and its formation mechanism under various loads show that the change of subsurface crack morphology of BK7 glass is caused by the change of the loading direction of abrasive particles and the dynamic properties of the material. On this basis, the effects of grinding parameters and grinding wheel parameters on the maximum depth of subsurface cracks are obtained through experimental research, which provides a basis for the establishment of a prediction model for the maximum depth of subsurface cracks. Effective prediction of the maximum depth of subsurface cracks is the key to reduce the length of subsequent grinding and polishing of parts, improve machining efficiency and improve grinding quality. Based on the above analysis conclusion and research, the prediction model of maximum depth of subsurface crack in ultrasonic vibration grinding BK7 optical glass is established by using least square support vector machine and Gao Si process regression method respectively. The validity of the two prediction models is verified by grinding experiments, and the prediction accuracy is compared. It provides the foundation and basis for optimizing the technological parameters of ultrasonic vibration grinding of optical glass materials.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ171.68

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