Chen Shaoshan, He Deyu, Wu Yi, Chen Huangfei, Zhang Zaijing, Chen Yunlei
Appl Opt. 2016 Oct 1;55(28):8056-8062. doi: 10.1364/AO.55.008056.
A new non-aqueous and abrasive-free magnetorheological finishing (MRF) method is adopted for processing potassium dihydrogen phosphate (KDP) crystal due to its low hardness, high brittleness, temperature sensitivity, and water solubility. This paper researches the convergence rules of the surface error of an initial single-point diamond turning (SPDT)-finished KDP crystal after MRF polishing. Currently, the SPDT process contains spiral cutting and fly cutting. The main difference of these two processes lies in the morphology of intermediate-frequency turning marks on the surface, which affects the convergence rules. The turning marks after spiral cutting are a series of concentric circles, while the turning marks after fly cutting are a series of parallel big arcs. Polishing results indicate that MRF polishing can only improve the low-frequency errors (L>10 mm) of a spiral-cutting KDP crystal. MRF polishing can improve the full-range surface errors (L>0.01 mm) of a fly-cutting KDP crystal if the polishing process is not done more than two times for single surface. We can conclude a fly-cutting KDP crystal will meet better optical performance after MRF figuring than a spiral-cutting KDP crystal with similar initial surface performance.
由于磷酸二氢钾（KDP）晶体硬度低、脆性高、温度敏感且具有水溶性，因此采用一种新的非水且无磨料的磁流变抛光（MRF）方法对其进行加工。本文研究了初始单点金刚石车削（SPDT）加工后的KDP晶体在MRF抛光后表面误差的收敛规律。目前，SPDT工艺包括螺旋切削和飞刀切削。这两种工艺的主要区别在于表面中频车削痕迹的形态，这会影响收敛规律。螺旋切削后的车削痕迹是一系列同心圆，而飞刀切削后的车削痕迹是一系列平行的大圆弧。抛光结果表明，MRF抛光只能改善螺旋切削KDP晶体的低频误差（L>10 mm）。如果单面抛光过程不超过两次，MRF抛光可以改善飞刀切削KDP晶体的全范围表面误差（L>0.01 mm）。我们可以得出结论，与具有相似初始表面性能的螺旋切削KDP晶体相比，飞刀切削KDP晶体在MRF成型后将具有更好的光学性能。
