Low-cost and precise magnetorheological fabrication of miniature glass optics

This paper presents an innovative magnetorheological (MR) fabrication method for directly generating precision miniature glass optics without the need of precision grinding. In this method, the optimized rotating small ring-shaped permanent-magnet tool (PMT) enhanced the viscosity of the MR slurry with abrasives inside the working gap between the workpiece material and PMT, thereby achieving the non-contact removal of the workpiece materials. Through a combination of theoretical analysis and experimental tests, the PMT with axial magnetization has been selected to generate a high-performance Gaussian-like tool influence function. The effects of the working gap widths, spindle speeds, and dwell time on the material removal behavior were systematically studied through a self-developed three-axis MR fabrication system. Accordingly, a gap width of 0.4 mm and a spindle speed of 800 rpm were recommended to balance the material removal rate and the alignment complexity. By precisely controlling the dwell time, ultra-smooth surfaces with form errors of around 21.538 nm, 101.043 nm, and 396.170 nm (rms) were achieved for fabricating the planar, spherical, and freeform surfaces on flat K9 glasses, respectively. The results demonstrate the effectiveness of the proposed MR fabrication method for the low-cost fabrication of miniature optics with complex shapes.