熔石英玻璃磁辅助抛光技术：材料去除机制与表面质量研究

1 引言

Fused silica glass, as a typical wide bandgap dielectric material, is widely used in the fabrication of devices such as gratings, vacuum windows, shielding plates, and lenses. To achieve high-precision batch production of fused silica glass, the manufacturing process of 'grinding → precision polishing → ultra-precision polishing' is widely adopted both domestically and internationally. Among them, polishing, as the last step in the precision/ultra-precision manufacturing process of optical materials, plays a crucial role in the processing quality and surface integrity of the components.

Traditional chemical mechanical polishing (CMP) technology utilizes the coupling of chemical energy and mechanical energy to achieve a smooth and flat surface. However, due to the normal cutting action of abrasive particles on the workpiece during processing, scratches, micro-cracks, or pits are easily generated below the surface. These defects are extremely prone to inducing melting and explosive damage to the material under strong laser irradiation. In recent years, magnetic-assisted polishing technology, which utilizes fluid dynamic pressure shearing for material removal, has attracted extensive attention from researchers both domestically and internationally and has gradually developed into a processing method for 'near-zero' defect surfaces of high-power optical components.

According to the different magnetic particles (micron-sized iron powder or nano-sized Fe3O4) in the polishing liquid, magnetic-assisted polishing technology can be mainly divided into three types: magnetorheological fluid (MRF), magnetic fluid (MF), and magnetic compound fluid (MCF) polishing. Magnetic-assisted polishing utilizes magnetic particles, non-magnetic abrasive particles, cellulose, and deionized water to form a viscous semi-solid flexible polishing head. The abrasive particles below the polishing head come into contact with the workpiece, move relatively, and perform micro-cutting to achieve low-damage, high-precision polishing. Shi et al. analyzed the feasibility of elastic MRF polishing based on the theory of elasto-plastic deformation and achieved chemical-dominated elastic magnetorheological polishing of large-aperture fused silica glass by changing the composition of the magnetorheological fluid and polishing parameters, eventually obtaining a super-smooth surface with a roughness Ra of 0.167 nm. Jiang et al. compared the differences in the normal polishing force, tangential polishing force, material removal rate, and surface roughness of the workpiece during traditional MCF polishing and ultrasonic-assisted MCF polishing. The results show that ultrasonic-assisted polishing is beneficial for improving the material removal rate and surface smoothness of the workpiece. Guo et al. found that during end-face MCF polishing, the material removal rate of BK7 glass is positively correlated with the rotation speed of the carrier liquid disk and negatively correlated with the polishing gap. They also established a material removal rate model related to the tangential and normal forces of the workpiece. The above research has investigated the material removal mechanism and surface quality formation mechanism of magnetic-assisted polishing technology both theoretically and experimentally, promoting the application of magnetic-assisted processing technology in the field of optical manufacturing.

This paper utilizes magnetic polishing liquid with different polishing gaps and iron powder volume ratios to process fused silica elements for different durations of magnetic-assisted polishing. The material removal rate, surface roughness, and transmittance of fused silica are analyzed and evaluated. Combined with the simulation calculation of spatial magnetic induction intensity, the effects of spatial magnetic induction intensity and iron powder volume ratio on material removal efficiency and surface quality are clarified, and a polishing process of 'small polishing gap + high iron powder ratio polishing liquid → large polishing gap + low iron powder ratio polishing liquid' is proposed, providing a theoretical basis and technical support for realizing efficient and low-defect processing of high-power laser components.

2 Experiment

2.1 Sample preparation

In this experiment, a self-developed circular polishing machine was used to perform magnetic-assisted polishing on fused silica glass elements. The polishing equipment is shown in Figure 1. A horizontal main shaft drives a ring-shaped Nd-Fe-B magnet with a magnetic flux density of 0.4 T at a speed of nt to rotate, forming a dynamic spatial magnetic field. A ring-shaped polylactic acid resin (PLA) baffle is installed on each end face of the magnet. The magnet and the baffle have the same outer diameter of 40 mm and inner diameter of 25 mm, with thicknesses of 8 mm and 4 mm, respectively. The ring-shaped baffle and the ring-shaped magnet together constitute the polishing wheel, with a polishing gap δ between the polishing wheel and the workpiece below it. Fused silica glass with a size of 40 mm × 40 mm × 5 mm is used as the processing object. Before polishing, the workpiece is double-sided ground with W5-W10 silicon carbide, with an initial surface roughness Ra of 0.2-0.25 μm and a subsurface crack depth of less than 4.5 μm.

内容：

Fused silica glass
Wide bandgap dielectric material
Gratings
Vacuum windows
Shielding plates
Lenses
Manufacturing process
Grinding
Precision polishing
Ultra-precision polishing
Optical material
Magnetic-assisted polishing technology
Chemical mechanical polishing technology
Abrasive particles
Scratches
Micro-cracks
Pits
Magnetorheological fluid
Magnetic fluid
Magnetic compound fluid
Magnetic microparticles
Semi-solid flexible polishing head
Roughness
Material removal rate
Surface smoothness
Elasto-plastic deformation theory
Spatial magnetic induction intensity
Iron powder volume ratio
High-power laser components
Polishing gap
Circular polishing machine
Rubidium iron boron
Nd-Fe-B
Polylactic acid resin
PLA
Polishing wheel
Silicon carbide double-sided grinding
Initial surface roughness
Subsurface crack depth
Workpiece