Study on traceability and suppression method of medium-frequency error for ultra-precision machining optical crystals

Area of Science:

• Materials Science
• Mechanical Engineering
• Optical Engineering

Background:

• Medium-frequency surface errors in ultraprecision flycutting impact optical crystal performance.
• A characteristic "knife-like grain" phenomenon is observed on machined optical crystal surfaces.

Purpose of the Study:

• To reveal the characteristic phenomenon of "knife-like grain" errors in ultraprecision flycutting.
• To identify the root cause of medium-frequency errors and their formation mechanism.
• To optimize control parameters for reducing these errors and improving surface quality.

Main Methods:

• Error traceability analysis to identify low-frequency fluctuations.
• Frequency domain waterfall diagram of vibration signals.
• Spindle speed signal analysis and theoretical/experimental exploration of cutting amount variations.
• Optimization of aerostatic spindle control parameters based on mechanical-electrical coupling.

Main Results:

• A periodic low-frequency fluctuation (0.3 Hz) between tool tip and workpiece identified as the cause of "knife-like grain" errors.
• Spindle speed fluctuation during cutting confirmed as the source of the surface characteristic.
• The formation mechanism of medium-frequency errors in flycutting was elucidated.
• Optimized aerostatic spindle control significantly improved root mean square (RMS) values in the medium frequency band.

Conclusions:

• Spindle speed fluctuation is the primary cause of "knife-like grain" medium-frequency errors in ultraprecision flycutting.
• Optimizing aerostatic spindle control parameters effectively mitigates these errors.
• The study provides a mechanism for reducing surface defects and enhancing optical crystal performance.