Ultra-Precision Vertical Spindle Grinder for Ceramics

在不久的将来，零热膨胀系数的单晶和微晶玻璃有望被超精密加工。这些材料由于其脆性的机械性能而被研磨和抛光。本研究旨在开发一种新型的超精密立式主轴磨床，它可以将陶瓷材料加工成尺寸精度为亚微米的平面镜面。在磨削加工过程中，控制被磨材料、砂轮和机床的热膨胀是获得亚微米级精度的关键。本研究试图通过采用零膨胀系数微晶玻璃作为砂轮主轴材料，控制室内温度、磨削水和静压油，使机床、砂轮和工件的温度均匀，从而降低砂轮的热膨胀。由于玻璃陶瓷主轴的脆性和昂贵的加工成本，还没有人开发出这种主轴。通过开发新的铸造和热处理工艺，对微晶玻璃的磨削性能和抛光性能进行检测，设计制造了第一台零膨胀系数微晶玻璃磨削主轴。磨削过程中的切割深度以0.1微米/脉冲为单位进行数字控制，这是由砂轮和工作台的刚性主轴和轴承执行的。静压油轴承的设计和制造具有低热膨胀、高刚性和高回转精度的特点。用该磨床获得了平整度为0.08微米、表面粗糙度为0.015微米的锰锌铁氧体单晶表面。通过研制修整和砂轮，该机可获得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.