Suratwala T, Menapace J, Tham G, Steele R, Wong L, Ray N, Bauman B, Gregory M, Hordin T
Appl Opt. 2021 Feb 1;60(4):1041-1050. doi: 10.1364/AO.415376.
The influence of workpiece curvature on the tool influence function spot during polishing of fused silica glass with cerium oxide slurry, while using a rotating hemispherical pad-foam tool for a wide variety of process conditions (tool displacement, inclination angle, and rotation rate), has been investigated. (Workpiece curvature ranged from 500 mm radius concave to 43 mm radius convex.) The TIF spot decreases in diameter and increases in the peak removal rate on more convex workpieces. In contrast, the TIF spot increases both in diameter and peak removal rate on more concave workpieces. For the range of workpiece curvatures investigated, both the spot size and the peak removal rate changed significantly, as much as 2 times. An elastic sphere-sphere contact mechanics model, which utilizes both a modified displacement (that leads to a change in the applied load) as well as a mismatch factor (that influences the pressure distribution shape), has been developed. The model was validated using both offline load-displacement measurements and finite-element analysis simulations. The model quantitatively describes the measured change in the relative contact diameter and relative pressure distribution, as well as semiquantitively describes the change in the relative volumetric removal rate on a large variety of TIF spots. The change in the volumetric removal rate for convex workpieces is a result of the balance between a decreasing spot size (reducing removal) and an increasing peak pressure (increasing removal), which usually results in relatively small changes in volumetric removal. In the case of concave workpieces, the volumetric removal rate change is also governed by a similar balance, but the spot size increase contribution dominates, resulting in a significant increase in volumetric removal rate. Understanding these trends can enable methods to add greater determinism during the fabrication of freeform optics by adjusting polishing parameters (such as dwell time) while the tool translates along a workpiece surface with different local curvatures.
研究了在使用旋转半球形泡沫抛光垫工具对熔融石英玻璃进行抛光的各种工艺条件（工具位移、倾斜角度和旋转速度）下，工件曲率对氧化铈浆料抛光过程中工具影响函数光斑的影响。（工件曲率范围从半径500mm的凹面到半径43mm的凸面。）在曲率更大的凸面工件上，工具影响函数光斑直径减小，峰值去除率增加。相反，在曲率更大的凹面工件上，工具影响函数光斑的直径和峰值去除率均增加。在所研究的工件曲率范围内，光斑尺寸和峰值去除率都有显著变化，高达2倍。已开发出一种弹性球-球接触力学模型，该模型既利用了修正位移（导致施加负载发生变化），也利用了失配因子（影响压力分布形状）。该模型通过离线负载-位移测量和有限元分析模拟进行了验证。该模型定量描述了相对接触直径和相对压力分布的测量变化，并半定量描述了各种工具影响函数光斑上相对体积去除率的变化。凸面工件体积去除率的变化是光斑尺寸减小（去除量减少）和峰值压力增加（去除量增加）之间平衡的结果，这通常导致体积去除量的相对较小变化。对于凹面工件，体积去除率的变化也受类似平衡的控制，但光斑尺寸增加的贡献占主导，导致体积去除率显著增加。了解这些趋势有助于在制造自由曲面光学元件时，通过在工具沿具有不同局部曲率的工件表面平移时调整抛光参数（如驻留时间），增加加工的确定性。
