NASA Marshall Space Flight Center has developed a numerically controlled grinding tool that eliminates undesirable periodic variations in surface contours in optical and other surfaces — such as mid-spatial frequency errors — that result from polishing. It can also be used to eliminate any undesirable irregularities in optical surfaces — either flat, curved, or aspheric — as well as other precision surfaces such as orthopedic joint replacements.
Because the tool can be integrated with CNC machining, it eliminates the tedious and imprecise hand polishing that has often been relied upon, while avoiding added errors due to over-polishing. The NASA Marshall invention makes use of a template fabricated via 3D printing that encapsulates diamond pellets and fits over a CNC tool head. The unique design solves the problems associated with similar, commercially available designs where other types of fixtures articulated, or gave way too much, rendering those previous tools ineffective. By encapsulating the diamond pellets in a 3D-printed template whose stiffness and articulation can be controlled by air pressure and thickness, mid-spatial frequency errors are eliminated at their source.
The tool was originally developed to address recurring issues in fabricating UV and X-ray optical surfaces, but can be used for visible-range optical surfaces or for any surface that requires precision finishing, whether curved, flat, or aspheric. This could include medical devices like artificial joints, as well as semiconductor wafers, sapphire windows, and many others. By reducing the processing time in polishing complex surfaces by as much as half, the NASA invention can also reduce costs.
Using the NASA tool, very low arc-second-resolution mirrors can be fabricated on a robotic polisher. The tool can be set up and used in less than one day, and can be rebuilt quickly, with few components requiring replacement. The tool can be used on glasses, metals, and other materials used for optics and precision surfaces.