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Infrared silicon diffractive machining

Goal:
Demonstrate the capability to manufacture an infrared silicon lens with 15 diffractive zones, meeting surface finish, form accuracy, and absolute radius specifications.

Process:
Using a Nanoform® X with an inner enclosure, to contain water-based coolant, or Nanoform® 250 ultra grind, specifically designed for flood coolant applications, to manufacture a multi-zone aspheric diffractive silicon lens.


Part Details:
Material:
Optical grade silicon
Diameter: 43.0 mm
Base radius: 107.787 mm ( 0.037 mm)
Center thickness: 6.0 mm


               Part photo on Taylor Hobson Form Talysurf 

Diffractive Details:
Zones:
15 Zone diameter tolerance: 0.02 mm
Zone depth: 1.2 µm


Process Details:
Tool:
0.2 mm radius, negative rake diamond tool
Spindle speed: 3500 rpm
Feed rate: 2.0 mm/min
Depth of cut: 4.0 µm
Coolant: Water-based

Results:
• Surface finish: 1.04 nm Ra
• Form accuracy: 56.1 nm RMS
• Fitted base radius: 107.783 mm




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