Page 145 - Chalcogenide Glasses for Infrared Optics

122 Cha pte r F i v e

5.3 Polishing
AMI has 22 spindles in operation, a small number in comparison to
an optics fabrication shop. The spindles are used mostly for polishing.
The polishing slurry used is mostly based on aluminum oxide with
some silica and zirconium oxide. The slurry is pumped and circulated
over the parts during polishing. Single-spindle operation requires a
lot of attention by the technician and thus is not very efficient. AMI
developed a multiblocking technique to increase production of the
small 1-in- diameter planoconvex sensor lenses.
First, one side of each blank is polished and then covered with a
protective coating of paint. Next, they are mounted in their respective
tool using a soft blocking wax. Figure 5.4 shows two spindles with mul-
tiple lens blanks blocked in the recesses on the spherical convex surface
of the tool. The smaller tool is for lenses with shorter focal lengths and
thus a smaller radius of curvature. Fewer lenses may be made at one
time than with the other tool used for longer focal length lenses. Here the
radius of curvature is larger, requiring a larger convex sphere. These two
tools are placed on the bottom vertical spindles. Not shown is the top
concave tools with the exact radius of curvature for their respective
lenses. The bottom spindles are rotated and the top spindles moved back
and forth while the bottom tools are spinning. Of course a polishing
solution is sprayed on all the parts at the same time. After the polishing
is finished, the lenses are unblocked in an oven. After cooling, they are
placed in an ultrasonic cleaner with a solution that removes all the wax
and paint. Each lens is then checked for curvature and center thickness.

FIGURE 5.4 Multiblocked Amtir 1 planoconvex 1-in lenses.