Common Mistakes in Optical Grinding &Polishing

Aperture Surface Deviation

(1) Causes of low aperture

①. The sand hanging aperture is too thin (the concave R is small, and the convex R is large).

②. The contact between the grinding dish and the lens is too loose, and the center of the lens is ground too much.

③. The diameter of the grinding dish is too small.

④. The swing range is too large or the skew (eccentricity) of the skewer is wrong – too large.

⑤. The negative LAP dish is too strong or the repair time is too long.

⑥, too much pressure on the fixture.

⑦. The chamfer is too sharp.

⑧. Ball center adjustment is too low.

Method:https://opticst.com/precision-optics/

① When sand hanging, strictly control △h or check the aperture with the original device, and it should not be too fine.

②. Trim the grinding dish so that the lens matches the grinding dish, and it should be slightly tight (strive to contact the entire surface)

③. Replace the grinding dish and choose the appropriate diameter (the diameter of the grinding dish is about 1.5 to 2 times the diameter of the lens)

④. Reduce the swing range and adjust the deflection position (adjust to the center of the dish)

⑤. Control the grinding time, and the swing and pressure should be stable and appropriate.

⑥, put down the pressure.

⑦, CG chamfer adjustment.

⑧, raise the ball core.

(2) Causes of high aperture

①. Sand hanging aperture is too thick (convex surface R is small) (concave surface R is large)

②. The contact between the grinding dish and the lens is too tight, and the edge of the lens is ground more.

③. The diameter of the grinding dish is too large.

④. The swing range is too small, and the swing eccentricity is too small (too close to the center).

⑤. The positive LAP dish is too strong or it has been repaired with the positive dish for too long.

⑥. The center of gravity of the upper jig is too high, and the vibration is too large during processing, so that the grinding amount of the edge of the lens is large.

⑦. The size of the cooling water may not enter the center of the grinding dish.

Method

①. Strictly control △h when hanging sand or check the aperture with the original device, and it should not be too thick.

②. Trim the surface shape of the grinding dish so that the lens and the dish match well.

③. Select or design and process a suitable grinding dish diameter.

④ Increase the swing and adjust the displacement of the eccentricity to increase the amount of grinding in the center of the lens.

⑤. Re-calibrate the strength of the LAP dish, and choose an appropriate repair time when trimming the grinding dish.

⑥. Properly reduce the height of the upper fixture without affecting the life of the clamping and upper fixture.

⑦. Increase the swing of the cooling water adjustment.

(3) The cause of the concave (concave center or local low)

①. The sand hanging aperture is too low and has not been ground to the center.

②. The contact between the lens and the grinding dish is too loose, and the center grinds too much.

③. The R value of the grinding dish (substrate) is not suitable, the radius of the convex dish is too small, and the radius of the concave dish is too large.

④. The swing range is not suitable, and the swing range and deflection angle are too large; the center of rotation of the grinding dish gathers grinding powder due to the small centripetal force.

⑤. Too much pressure is applied to the lens with small central thickness.

⑥. The R value of the fixture is wrong, and the center is suspended.

⑦. The swing position is too close to the center.

Method

①. Control the sand hanging aperture, and detect the surface shape at any time during processing.

②. Trim the grinding dish to make the lens fit well with the grinding dish.

③. Replace or trim the grinding dish so that the radius of curvature meets the design requirements.

④ Adjust the swing range, generally reduce the swing range and eccentric displacement or perform symmetrical swing to reduce or eliminate the concave psychology; the brush removes the grinding powder in the center.

⑤. Properly raise the skewer or lower the pressure.

⑥, correction jig.

⑦. Adjust the deviation and swing.

(4) Reasons for medium height (concave center or local height)

①. The contact between the lens and the grinding dish is too tight, and the center is not ground.

②. The center of the grinding dish is low, and the amount of grinding at the center is insufficient.

③. The swing range is too small or the eccentric displacement is too small.

④. The radius of the grinding dish (substrate) is not suitable, the radius of the convex dish is too large, and the radius of the concave dish is too small.

⑤. The R value of the fixture is not suitable, the center is too high and the top lens is placed.

⑥, the swing is too close to the edge of the dish.

Method

① Dress the grinding dish so that the lens and the grinding dish have a good match.

② Trim the surface shape of the grinding dish to make the surface shape of the grinding dish regular.

③Adjust the swing range to make the swing range and eccentric displacement suitable.

④Replace the grinding dish and choose a suitable radius of curvature.

⑤ Correct the R value.

⑥Adjust the swing.

(5) Causes of vertical edge (stepping edge)

①. The edge of the lens is in too tight contact with the dish, resulting in too much grinding of the edge of the lens.

②. The surface shape of the grinding dish is irregular, and the elasticity is inconsistent when grinding.

③. The edge is too much ground when sand hanging, and it has not been completely eliminated during grinding.

④, the sand hanging aperture is too thick, the grinding is reduced from the high aperture, and the edge has not been ground yet.

⑤. The radius of curvature of the grinding is not suitable, the radius of the convex dish is too large, and the radius of the concave dish is too small.

⑥. The diameter of the grinding dish is too large.

⑦. The edge of the LAP dish is too strong.

Method

①. Trim or lightly scrape the edge of the grinding dish, and continue to grind so that the lens and the dish have good contact.

②. Repair the grinding dish and continue to grind. The lens surface and the dish should be in good contact, and the tightness should be the same.

③. Control the surface shape of the sand hanging. If the sand hanging appears, it should be corrected immediately and not flow to the grinding.

④. The sand hanging aperture cannot be made coarser than the grinding, it can be slightly lower by 1~2.

⑤. Replace the grinding dish and choose a suitable radius of curvature.

⑥. Consider the diameter of the grinding dish according to the diameter of the lens and the radius of curvature.

⑦. Repair uniform LAP dishes.

(6) Aperture N and partial aperture △N (outline) Causes

①. The diameter of the grinding dish (depth) is too small.

②. The surface of the grinding dish is too smooth.

③. The grinding liquid is too light, and the heat is too high when grinding.

④, the size of the swing is not appropriate.

Method

①. Adjust (replace) the grinding dish and choose the appropriate diameter.

②. Re-finish the surface with a LAP dish.

③. Adjust the concentration of the grinding liquid, and open a few more grooves on the surface of the grinding dish.

④, Appropriately increase the swing range.

(7) Ellipse (dispersion) causes

①. The surface of the grinding dish is irregular, and it is loose and tight when grinding, which makes the lens rotate unevenly.

②. The skewer is too skewed, and the swing range is asymmetrical with respect to the rotation center of the main shaft.

③. The coupling of the spindle speed and the swing speed makes the movement track of the lens (grinding dish) often overlap, so that the grinding of the lens surface has a certain directionality.

④. The grinding dish and lens fit too tightly.

⑤. The fit between the lens and the jig is too tight, and the rotation is not flexible.

⑥. The jig backing paper is stacked unevenly.

⑦, sand hanging NR ellipse failed to grind.

Method

①. Use a LAP dish to trim the surface of the grinding dish, and then process the lens after the surface of the grinding dish is regular.

②. Adjust the swing amplitude so that the lens swings symmetrically with the center of rotation.

③. Adjust the spindle speed or swing speed to change the original motion track.

④. Trim the surface shape of the grinding dish, so that the grinding dish and the lens have a good fit.

⑤. Refit the supporting ring.

⑥. Replace the backing paper.

⑦. Sand back and hang up for repair.

(8) Causes of deformation

①. The surface shape of the grinding dish is seriously irregular.

②. The accuracy of the surface shape of the finished sand hanging product is seriously exceeded.

③ There are many broken places on the grinding dish.

④, the rotation of the upper fixture is not flexible

Method

①. Trim the surface of the grinding dish evenly.

②. Ensure the accuracy of the surface of the sand hanging product.

③. Replace the grinding dish with a new one.

④. Replace the grinding dish or the upper jig to ensure that the upper jig can turn flexibly.

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