Machining approach of freeform optics via fast tool servo diamond turning

Optical freeform surfaces can provide a higher degree of freedom in optical design, compared with spherical and aspherical optical components. The application of freeform optical components in imaging optical systems is conducive to simplifying the system structure and improving imaging quality, and has wide applications in illumination, imaging and non-imaging, etc. This paper introduces the basic principle and process of fast tool servo (FTS) diamond turning, and its application in the field of optical processing. A series of machining experiment was carried out on aluminum materials by FTS diamond turning for XY polynomial freeform surface mirrors, and the surface accuracy and roughness were measured. The effects of feed rate, spindle speed, and cutting depth on surface roughness were studied and corresponding functional relationship curves were determined. The results show that the feed rate had the greatest influence on surface roughness of aluminum freeform surfaces, as the feed rate increased, the surface roughness increased gradually; the spindle speed and cutting depth have relatively little influence on surface roughness. The fitting degree of curves was very high, which can predict the surface roughness of machined freeform more accurately. The 3-D surface accuracy PV of the final processed freeform surface was 0.22μm, and the 2-D surface roughness Ra value was 3.5nm, the machined surface reached a mirror finish.