旋转磁场下非球面工件的磁性混合流体抛光

针对非球面光学元件的结构特点及其表面质量要求，在磁性混合流体抛光基础上，设计并制作以径向充磁永磁体为旋转磁场源的半球头抛光头。首先，通过Ansoft Maxwell磁场仿真，分析对比不同形状、不同尺寸磁体和偏心距下各磁体周围磁场的分布状况，选定直径为10.0 mm、高度为5.0 mm、偏心距为2.5 mm、径向充磁的圆柱形磁体。其次，通过观测并比较不同组成、配方和供应量的磁性混合流体在抛光头上的行为，确定磁性混合流体抛光液成分。最后，采用制备的磁性混合流体抛光液及自制的抛光头对非球面PMMA工件进行抛光试验。经过15 min抛光后，PMMA工件表面质量明显改善，其面型精度R_q由0.703 μm下降到2.433 nm，表面粗糙度R_a由0.545 μm下降到1.786 nm，说明研制的抛光头能实现非球面工件的纳米级抛光。 

Magnetic compound fluid polishing of aspheric workpiece under rotating magnetic field

According to the structural characteristics and the surface quality requirements of aspheric optical elements, a hemispherical head polishing head with radial magnetized permanent magnet as rotating magnetic field source is designed and manufactured on the basis of magnetic compound fluid (MCF) polishing. Firstly, through Ansoft Maxwell magnetic field simulation, the distributions of magnetic field around each magnet with different shapes, sizes and eccentricities are analyzed and compared, and the cylindrical magnet with diameter of 10.0 mm, height of 5.0 mm, eccentricity of 2.5 mm and radial magnetization is selected. Secondly, by observing and comparing the behaviors of MCF with different compositions, formula and supplies on the polishing head, the compositions of MCF polishing slurry is determined. Finally, the aspheric PMMA workpiece is polished with the prepared MCF polishing slurry and the self-made polishing head. After polishing for 15 min, the surface quality of the PMMA workpiece is significantly improved, its surface accuracy R_q is decreased from 0.703 μm to 2.433 nm, and the surface roughness R_a is reduced from 0.545 μm to 1.786 nm, indicating that the developed polishing head can realize the nano-polishing of aspheric workpiece.