Smoothing tool design and performance during subaperture glass polishing

Area of Science:

• Optics and Surface Metrology
• Materials Science and Engineering
• Manufacturing Processes

Background:

• Subaperture tool grinding and polishing can cause mid-spatial frequency (MSF) errors, appearing as surface ripples.
• These MSF errors often necessitate a separate smoothing polishing step for correction.

Purpose of the Study:

• Design and test flat multi-layer smoothing polishing tools.
• Achieve simultaneous reduction of MSF errors, minimization of surface figure degradation, and maximization of material removal rate.

Main Methods:

• Developed a time-dependent convergence model linking material removal to workpiece-tool height mismatch.
• Employed finite element mechanical analysis to determine interface contact pressure distribution.
• Evaluated tool designs based on material properties, thickness, pad texture, and displacement.

Main Results:

• Optimized smoothing tool performance by adjusting the gap pressure constant (h¯) for different spatial scales.
• A two-layer tool with a grooved polyurethane pad and foam underlayer showed superior performance.
• The best design utilized a thin, grooved IC1000 pad (E=360 MPa), thicker blue foam (E=5.3 MPa), and 1 mm displacement.

Conclusions:

• The optimized two-layer smoothing tool effectively addresses MSF errors without compromising surface figure.
• This approach offers a high material removal rate, improving the efficiency of the polishing process.
• The study provides a framework for designing advanced smoothing tools for precision optics manufacturing.