Single Point Diamond Turning (SPDT) is a manufacturing process used to quickly produce low to moderate volumes of highly accurate plastic optics, usually to support R&D or prototyping efforts. The machine that does the single point diamond turning is a precision CNC lathe. The cutting tool is a diamond that has been specially prepared to cut the required surface geometry of the lens. Diamond turning is used to create light weight aspheric plastic lenses, and is capable of cutting freeform polymer optics as well. Because the surface is generated on a CNC lathe, the process is very deterministic and highly repeatable, with surface form errors as low as 2 waves per 2.5 cm of diameter. Because the cutting tool is actually a diamond, surface finishes of 3 to 4 nanometers (Ra) are regularly achieved. With surface finishes this fine, the diamond turned optics are very specular, require no post-machine polishing, and can be readily coated with either a multi-layer thin film coating, for enhanced transmission, or metalized with Aluminum, Gold or Silver for use as a first surface mirror. GS Plastic Optics coats all of its diamond turned lenses and mirrors at its in-house thin film coating facility.
Many different polymers can be diamond turned directly. A partial list would include: Acrylic (PMMA), COC (Topas), COP (Zeonex and Zeonor, APEL), Styrene, Polyester (OKP-4), Polyetherimide (Ultem) and other select polymers. Some plastics such as polycarbonate are not suitable for diamond turning because they are too soft. It is important to discuss material choices with your diamond turning supplier at the outset of the project. The team at GS Plastic Optics is happy to assist you to find the right materials to rapidly create your light weight plastic aspheric lens.
There are several key advantages to consider when deciding to use diamond turning as a solution for validating new designs. These include: Speed of delivery, reduced tooling costs, high accuracy and sophisticated surface profiles. At GS Plastic Optics, we can deliver coated prototype custom optics made by diamond turning with lead-times ranging from 3 weeks to 5 weeks. This will allow you to have high quality precision samples in hand quickly for system testing. Diamond turned plastic prototype lenses require less tooling in fabrication than injection molding. As a result both non-recurring costs and overall manufacturing lead-times are reduced. Diamond turned plastic optics are very accurate. Because of the high accuracy and precision of the turning equipment, form-errors and surface finishes created by this process are very tightly controlled. It is possible to create complex surface geometries, such as off-axis aspheric surfaces and CAD-driven Freeform surfaces right into the polymer optic.
We measure and certify all of our diamond turned optics in our extensive in-house metrology lab. The lab has a Zygo interferometer, Zeiss contact profilometer, two different styles of CMM and a Bruker white light interferometer. You can be assured that the light weight aspheric polymer optics that you have ordered will be within tolerance.
Because GS Plastic Optics has in-house capability to provide both single point diamond turning and thin film coating of polymer optics, we are unmatched in our ability to rapidly deliver finished prototypes.