Research on single point diamond turning of chalcogenide glass aspheric lens

Chalcogenide glass (ChG) Ge₂₂Se₅₈As₂₀ is a significant material in infrared optical systems, and it is usually machined by ultraprecision single point diamond turning (SPDT) for aspheric lens and freeform surface. However, as a soft brittle material, the surface is easily cracked during cutting. With the increasing demand for imaging quality, the surface integrity of chalcogenide glasses becomes increasingly important. This paper proposes a method to achieve high-precision and high-efficiency aspheric lens by SPDT. First, to study the material properties, the Vickers hardness of Ge₂₂Se₅₈As₂₀ is tested, and the element components and microstructure are analysed by EDS. Second, through orthogonal cutting, the critical cutting thickness of the brittle-ductile transition is tested to be 1.2 μm and the minimum depth of cut for chip formation of 100 nm is identified. The material removal rate under ductile machining in face turning was calculated. Finally, by optimizing the machining condition, an aspheric lens with surface roughness of Ra 6.47 nm and form error of PV 120.82 nm was successfully fabricated.