Optical Lens Grinding and Polishing Process: From Rough Grinding to Nanometer Surface
From blank to usable, an optical lens goes through six steps: cutting, rough grinding, fine grinding, polishing, coating and testing. What decides imaging quality is the polishing stage's ability to reach λ/10-class figure and nanometer-level surface roughness. This article breaks down each step's role and difficulties, and how modern small-tool figuring equipment stabilizes the accuracy.
1. Full Optical Machining Flow (flowchart)
Standard flow: cutting → rough grinding → fine grinding → polishing → coating → testing. The front end removes stock and sets shape, the middle corrects figure, the back end raises surface quality and functional coating.
Cutting → rough grinding → fine grinding → polishing → coating → testing
- Cutting: inner / outer circular saw or water jet cuts the blank to near-net size;
- Rough grinding: diamond pellets remove most stock, set thickness and outer diameter;
- Fine grinding: finer abrasive corrects figure initial value, leaves proper margin for polishing;
- Polishing: figuring to target figure and surface roughness;
- Coating: adds AR / reflective functional layers;
- Testing: interferometer for figure, microscope for defects.
2. Rough and Fine Grinding: Shaping and Damage Removal
Rough grinding removes 90%+ of the stock but introduces a deep surface / subsurface damage layer; fine grinding with finer abrasive thins the damage layer and brings the figure close to design, leaving controllable margin for polishing.
Removing stock, correcting figure initial value
Too much fine-grind margin lengthens polishing; too little leaves fine-grind damage unpolished. Margin is left by aperture and figure error , with online figure sampling controlling the pace.
3. Polishing: Small-Tool Figuring to Nanometer Level
Polishing uses a soft lap + slurry (cerium oxide etc.) for micro-removal while correcting figure.
Figuring-center principle, removal-function control
Modern small-tool figuring centers use the computer-controlled compliant-tool (CCOS) principle: from the figure-error map, plan the lap path and pressure so removal matches the need everywhere. The core is the removal function — material removed per unit path, which must be stable and repeatable.
How figure accuracy (PV/RMS) approaches λ/10
Figure is expressed by PV (peak-to-valley) and RMS (root-mean-square). Precision optics typically require RMS ≤ λ/10 (λ=632.8 nm ≈ 63 nm) . Small-tool figuring approaches this via an iterative "measure → correct removal map → re-polish" loop.
4. Surface-Quality Testing: Scratches, Digs and Figure
Interferometer for figure, microscope for surface defects
- Figure: Fizeau / Twyman interferometer generates a figure map, reading PV/RMS directly;
- Surface defects: dark-field microscope grades scratches and digs per standard (e.g. GB/T 1185);
- Roughness: white-light interferometer or profiler measures Ra to nanometer level.
5. Process Difficulties and Tuokun Equipment Approach
Difficulties are "large-aperture figure convergence is slow, edge effect, thermal deformation". Tuokun's gantry small-tool figuring center uses a high-stiffness frame + CCOS control to suppress edge effect; the robot polishing center suits flexible small-part production lines. Both use closed-loop figure correction, minimizing human dependence.
FAQ
Q: How precise can optical lens polishing get?
Precision optics figure can reach RMS ≤ λ/10 (≈63 nm), surface roughness Ra into nanometer level. It depends on equipment and aperture; the small-tool figuring center stabilizes this via closed-loop correction.
Q: Difference between small-tool figuring and ordinary polishing?
Ordinary polishing relies on experience and has poor consistency; small-tool figuring uses computer-controlled removal functions, removing material at targeted points per the figure-error map — repeatable accuracy, suited to production.
Q: How to read figure accuracy PV and RMS?
PV is the highest-minus-lowest difference, showing extreme deviation; RMS is the overall root-mean-square, showing integrated figure quality. Optical figure is usually judged mainly by RMS, with PV as supplement.
Summary
The precision ceiling of an optical lens is in polishing. Understand the division "rough grinding shapes, fine grinding removes damage, polishing corrects figure", then pair it with small-tool figuring's closed-loop control, to stably make λ/10-class, nanometer-surface elements. For equipment schemes, see the figuring-center product pages.