Selective laser melting, referred to as "Direct Metal Laser Sintering"(DMLS), "Metal Powder Bed Fusion" or "3D Printing" is an additive manufacturing process which allows extremely thin wall and complex structures. Off-axis aspherics are as easily produced as simple spherical optical surfaces. Nickel 11-13 % phosphorus alloy is the only hard, very fine grain, corrosion resistant material that can be diamond turned and polished to ultra smooth surfaces. Diamond turning produces any aspheric surface to visible optical tolerances. Finishes of 0.6nm rms have been diamond turned on NiP alloy without post polishing. Very low cutting force of diamond turning allows a mirror faceplate to be very thin without print-through of the internal support structure. The innovation uses proven steel, stainless steel and superalloy powder additive manufacturing to make mirror substrates with near perfect thermal expansion match with electroplated NiP coating. It is fabrication of low cost, light weight large aperture mirrors by three processes. 1. Additively manufactured mirror substrates very close to net shape. 2. Electroplated NiP alloy covers contours of the mirror substrates with thickness to allow diamond turning, no machining of mirror substrate required. 3. Diamond turning can produce the mirror segment contour to visible tolerances.
