Ultra-Precision Vertical Spindle Grinder for Ceramics

在不久的将来，有望实现零热膨胀系数的单晶和玻璃陶瓷的超精密加工。这些材料由于其易碎的机械性能而被研磨和抛光。本研究旨在开发一种新型超精密立轴磨床，可将陶瓷材料加工成尺寸精度为亚微米级的平面镜面。在磨削加工过程中，控制被磨材料、砂轮和机床的热膨胀是达到亚微米精度的关键。本研究试图通过两种方法来降低这种热膨胀，一是使用热膨胀系数为零的玻璃陶瓷作为砂轮主轴的材料，二是通过控制室内温度、磨削水和静液压力油，使机床、砂轮和工件的温度均匀。由于玻璃陶瓷主轴易碎，加工成本昂贵，目前还没有人研制出陶瓷主轴。通过对铸造和热处理新工艺的开发，以及对玻璃陶瓷的磨削性和抛光性的检验，设计并制造了第一台零热膨胀系数的玻璃陶瓷磨削主轴。磨削加工的切削深度以0.1微米/脉冲为单位，由砂轮和工作台的刚性主轴和轴承进行数控加工。设计和制造的静压油轴承具有热膨胀小、刚度高、转速精度高等特点。利用该磨床可获得平面度为0.08微米、表面粗糙度为0.015微米的锰锌铁氧体单晶表面。通过修整和砂轮的研制，可获得Rmax小于0.01微米的光滑表面。

Single crystals and glass ceramics of zero thermal expansion coefficient are expected to be machined ultra-precisely in near future. These materials have been lapped and polished because of their brittle mechanical properties. This research intends to develop a new ultra-precision vertical spindle grinder which can finish ceramic materials into flat mirror surfaces having sub-micron in dimensional accuracy. It is the most important to control the thermal expansion of materials to be ground, a grinding wheel and machine tool for getting the sub-micron accuracy in grinding process. This research tried to reduce such thermal expansion by two methods, that is, using of glass ceramics of zerothermal expansion coefficient as a material of a grinding wheel spindle and controlling the temperatures in room, grinding water and hydrostatic pressure oil for making the temperatures of a machine tool, grinding wheel and workpiece uniform. No body has developed a glass ceramic spindle because of brittleness and expensive cost for machining. By development of new casting ＆ heat treating processes and examination of grindability and polishability of the glass ceramics, the first grinding spindle made of glass ceramics having zero thermal expansion coefficient has been designed and manufactured. Depth of cut in grinding process is numerically controlled in the unit of 0.1 micron/pulse which is performed by the rigid spindles and bearings for a grinding wheel and table. Hydrostatic oil bearings are designed and manufactured having the features such as low thermal expansion, higher rigidity and higher revolutional accuracy. MnZn ferrite single crystal surfaces of 0.08micron in flatness and of 0.015 micron Rz in surface roughness were obtained by using this new grinder. By development of dressing and a grinding wheel, the smoother surface of less than 0.01 micron Rmax will be obtained by the machine.