小曲率凹面光学玻璃的磁性混合流体精密抛光

Magnetic compound fluid polishing of concave optical glass with small curvature

为实现小曲率凹球面光学玻璃的高效超精密抛光,充分发挥旋转磁场下磁性混合流体兼具黏度和粒子动态分布的特点,提出了一种新型半球头抛光装置。使用Ansoft Maxwell仿真分析轴向充磁圆柱永磁体及其上方分别加装平面铁块和凹面铁块3种磁源结构下的磁场分布,发现加装凹面铁块能强化“边缘效应”,获得更集中分布的大磁场区,进一步仿真优化磁体尺寸和偏心距。比较不同抛光液组分和磁体偏心距下的磁性混合流体行为,确定了抛光液的最佳组分以及磁体偏心距。最后,对曲率半径为15.4 mm、中心深度为2.24 mm的凹球面K9玻璃进行抛光实验,90 min后,面形精度RMS由0.719μm降低至11.7 nm,表面粗糙度Ra由0.552μm降低至9.656 nm。新型抛光装置能够实现小曲率凹球面工件的高效纳米级抛光。

To realize efficient ultra-precision polishing of concave spherical optical glass with small curvature,a hemispherical head polishing device based on magnetic compound fluid(MCF)with a high apparent viscosity and stable distribution is proposed.First,the magnetic-field distribution of three different magnetic sources(axial magnetized cylindrical permanent magnet with a planar iron board and concave iron board installed above it)is simulated with the use of ANSOFT Maxwell.It is found that the addition of the concave iron board can strengthen the corner effect,and the magnetic field can be more concentrated.The dimensions of the magnetic sources and magnet eccentricity are optimized according to the simulation results.Second,by observing and comparing the behavior of the MCF slurry with different compositions and magnet eccentricities on the polishing head,the composition of the MCF slurry and magnet eccentricity are determined.Finally,a polishing experiment is performed on the concave spherical K9 glass workpiece with a curvature radius of 15.4 mm and center depth of 2.24 mm using the optimized polishing solution and self-made polishing device.Following 90 min of polishing,the root-mean-square(RMS)of the workpiece surface is reduced from 0.719μm to 11.7 nm,and the surface roughness(Ra)is reduced from 0.552μm to 9.656 nm.It is verified that the designed polishing device can achieve efficient nanoscale polishing of concave spherical workpieces with small curvature.