High Efficient and High Quality Machining of Optical Glass by Ductile Mode Grinding

近年来，硅、玻璃等脆性材料的纳米加工研究引起了人们的关注。一种塑性变形的材料去除，称为延性模式加工，是通过非常小的切割深度实现的。当表面裂纹随切深的增加而出现时，通常被认为是脆性加工。本实验所用的工件材料为光学玻璃(BK7)。刀具采用顶角为136°的单晶Vickers金刚石锥体压头。超精密车床由用于工件回转的空气静压轴承主轴和用于刀具进给的滚子轴承滑块组成。以150~1500 m/min的恒切削速度，0.03 mm/转的恒进给速度，从中心向外进行面车削，形成螺旋槽。通过部分插入的间隔件…使安装的工件倾斜工件和卡盘表面之间的距离更大，以产生不同深度的凹槽。不仅在表面裂纹上观察到韧脆转变点，而且在亚表面裂纹上也观察到韧脆转变点。使用扫描力显微镜测量凹槽深度并观察表面裂纹。用激光扫描显微镜测量了斜切和刻蚀表面亚表面裂纹最深处的距离。次表面裂纹产生的深度为几nm，而基于表面裂纹的过渡点为400-700 nm。光学玻璃表面裂纹在过渡点附近突然扩展，单晶硅表面裂纹逐渐扩展。发现由次表面裂纹决定的韧脆转换点比由表面裂纹决定的韧脆转变点浅。因此，亚表面裂纹的评估将是重要的，尤其是在抛光过程中，

The studies on nano-scale machining of brittle materials, such as silicon and glass, have come into notice in recent years. A material removal with plastic deformation, known as ductile mode machining, has been achieved by a very small depth of cut. When surface cracks occurred with being increased the depth of cut, the machining has been commonly considered to be brittle mode. The workpiece material used in the present experiment is a optical glass (BK7). A single crystal Vickers diamond pyramid indentor with an apex angle of 136° is used as the cutting tool. The ultra precision turning machine consists of an aerostatic bearing spindle for workpiece revolution and a roller bearing slide for tool feed. Face-turning of the workpiece is done from the center to the outside with a constant cutting speed between 150 m/min and 1500 m/min and a constant feed rate of 0.03 mm/revolution, and a spiral groves are formed. An inclination is given to the mounted workpiece by a partly inserted spacer … More between the workpiece and the chuck surface in order to generate various depth of grooves. The ductile-brittle transition points are examined by the observations not only on the surface cracks but also on the subsurface cracks. A scanning force microscope is used for measuring the depth of the grooves and observing the surface cracks. The distance from the surface to the deepest point of the subsurface crack on obliquely sectioned and then etched surfaces are measured by a scanning laser microscope. The subsurface cracks are generated at a depth of a few nm, while the transition point based on the surface crack would be a depth of 400-700nm. The surface crack on optical glass expands suddenly over the transition point, while the surface crack on single crystal silicon expands gradually. It is detected that the ductile-brittle transition point determined by the subsurface cracks is shallower than that determined by the surface cracks. Therefore the evaluation of the subsurface cracks would be important especially in finishing, Less