Search

This study investigates a new semi-fixed-abrasive, ultra-fine finishing method for optical glass using a magneticcompound fluid (MCF) wheel. This MCF wheel generates a thin, uniform MCF slurry layer on the entire circumferentialsurface of a ring-shaped permanent magnet placed between two non-magnetic plates. The MCF slurry is composed ofnano-sized magnetite particles, micron-sized iron particles, several 10 μm-sized α-cellulose fibres and sub-micron-sizedabrasive particles that react to the magnetic field. Following modifications to the design of the MCF, experiments wereconducted to evaluate the performance of the modified wheel in spot-polishing fused silica glass. This paper describes themodifications to the MCF wheel and the experimental setup used to measure its performance. The improvement of themodified wheel over the unmodified wheel in terms of material removal and surfaces roughness is experimentallyconfirmed. The effects of the wheel rotational speed and the clearance between the wheel and the workpiece on materialremoval and the workpiece surface roughness are investigated. The polishing forces are measured, the structure of the MCFslurry is examined and the magnetic field distribution is analysed. A model of material removal in polishing with themodified MCF wheel is developed. The results indicate the following: (1) more material was removed, i.e., greater spotdepths, and better surfaces were obtained in the regions that were near the edges of the magnet; (2) the modified MCF wheelperformed much better than the unmodified wheel in terms of material removal and surface roughness, e.g., 3.1 μm vs. 1.7μm for the maximum spot depth, 0.04 mm3 vs. 0.0088 mm3 for the volume of material removed and Ra = 5.624 nm vs.14.67 nm for the surface roughness; (3) a better work surface and greater material removal were obtained with smallerworking clearances and higher wheel rotational speeds.

A kind of zirconia-coated carbonyl-iron-particles (CIPs), which show long-time stability against aqueous, is installed in magnetic compound fluid (MCF) to polish PMMA. Performance (normal polishing force and surface roughness) of zirconia-coated CIP based MCF slurry with different CIP concentrations is investigated. For comparison, the performances of the conventional non-coated CIP (i.e., HQ) based MCF slurry and MRF slurry in which DI-water is employed instead of MF are also examined. In the presence of Al2O3 abrasive particles, the use of zirconia-coated CIP based MCF slurry can not result in better polishing performances compared with conventional HQ CIP based MCF slurry; In the absence of Al2O3 abrasive particles, higher normal polishing force and smoother work-surface were obtained with the zirconia-coated CIP based MCF slurry rather than the MRF slurry; For the zirconia-coated CIP based MCF slurry without abrasive particles, the concentration of zirconia-coated CIP should be less than a certain value (in the current work, 70 wt. %), otherwise MCF slurry shows bad particle dispersion and is easily dried, resulting in the loss of its polishing ability.

Ultrasonic vibration assisted processing is well known for the improvement in machined surface quality and processing efficiency due to the reduced forces and tribology-generated heating when grinding hard-brittle materials. We transplanted this philosophy to chemo-mechanical fixed abrasive polishing of optical glass, namely fused silica, in an attempt to improve surface roughness and/or material removal rate. Experiments were conducted to elucidate the fundamental characteristics of chemo-mechanical fixed abrasive polishing of fused silica in the presence and absence of ultrasonic vibration on a setup with an in-house built gadget. The experimental results show that ultrasonic vibration assisted chemo-mechanical fixed abrasive polishing can yield increased material removal rate while maintaining the surface roughness of manufactured optics compared to conventional fixed abrasive polishing without ultrasonic vibration. The mechanism of material removal in fixed abrasive polishing was also delved. We found that the glass material is removed through the synergic effects of chemical and mechanical actions between abrasives and glass and the resultant grinding swarf contains ample Si element as well as Ce element, standing in stark contrast to the polisher that contains abundant Ce element and minor Si element.

This paper aims to develop an alternative novel technique for the high efficiency and ultrafine surface finishing of fused silica glass. A semi-fixed abrasive tool named MCF (magnetic compound fluid) wheel is produced by distributing a certain volume of MCF slurry uniformly over the whole circumference surface of ring-shaped permanent magnets. An experimental rig is constructed in house followed by experimental investigations involving effects of the MCF wheel construction and process parameters on the material removal and work-surface roughness. As a result, the performance of the developed MCF wheel in the surface finishing of fused silica glass has been confirmed, and the appropriate wheel construction and process parameters have been determined in terms of the material removal rate, the flatness of polishing area and the surface roughness, showing an extremely smooth work-surface with surface roughness of Ra0.92nm has been achieved successfully in the current work.