Surface Quality Challenges for CNC Machining of Optical Parts
Optical parts (such as lens molds, mirrors, light guide plate molds) require a surface roughness of Ra < 20nm, even to the optical mirror level. Traditional CNC milling is difficult to directly achieve this level and usually requires subsequent polishing. In 2026, single-point diamond turning (SPDT) and fly-cutting technology have become the mainstream methods of optical CNC. SPDT uses natural single-crystal diamond tools and is machined at extremely low feed rates (1-5μm/rev) and extremely high spindle speeds (4,000-10,000 rpm) on ultra-precision machine tools to directly obtain a surface of Ra < 10nm. The technology is suitable for aluminum, copper, nickel-phosphorus alloys, as well as optical plastics (PMMA, PC). In actual machining, the challenges come from: tool wear (diamond chemically reacts to steel materials), environmental vibration control (requiring ground-based vibration isolation), and temperature stability (±0 C). In 2026, optical CNC services will cost 5-10 times more than regular CNCs, but are indispensable in AR/VR lens molds, infrared optical windows, and lidar optical components. CNC service providers with optical machining capabilities are usually equipped with air bearing spindles, marble beds, and active vibration isolation systems.
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