石英玻璃的单颗磨粒划擦应力场解析模型及损伤可控磨削机理研究

Analytical Model for the Elastic Stress Field during Scratching and Controllable Precision Grinding Mechanisms of Fused Silica

构建了单颗磨粒划擦各向同性硬脆材料的弹性应力场解析模型,并以此为基础提出单颗磨粒划擦各向同性硬脆材料表面的裂纹失稳扩展临界函数,临界函数包含原始表面应变速率、磨削液等因素对裂纹扩展造成的影响。将石英玻璃作为研究对象,深入分析了表面微裂纹损伤的可控磨削机理。在进行石英玻璃的磨削试验中,材料的磨削机理随单颗磨粒磨削深度的增加而变化,依次是塑性域去除、低载半脆性域去除、全脆性域去除和高载半脆性域去除。在1 mm/min的工件进给速度下,可以对石英玻璃进行塑性域磨削,从而获得无裂纹损伤的光滑磨削表面,然而其磨削效率较低,在实际生产中不能发挥理想的作用。对石英玻璃开展全脆性域磨削时,材料去除率较高、加工表面表面质量好、微裂纹损伤深度较小,砂轮自锐性良好,是一种优良的精密磨削工艺。

An analytical model for the elastic stress field during scratching an isotropic hard brittle material is presented. A critical function for crack propagation for single grit scratching an isotropic hard brittle material is developed. The effects of original crack density on the surface, strain rate and grinding coolant are considered in the function. Controllable grinding mechanisms of surface micro cracks on fused silica are investigated based on the critical function for crack propagation. The grinding mechanisms variates from ductile mode to low-load semi brittle mode, full brittle mode and high-load semi brittle mode in sequence with the increasing single grit scratching depth. When the workpiece feed rate is low to 1 mm/min, fused silica is removed by crack-free ductile grinding, but the material removal efficiency is too low for practical fabricating of fused silica lens. While full-brittle grinding is a feasible precision process for its shallow subsurface damage, high efficiency and good self-sharpening of grinding wheel.