Aspherical Surface Machining by Single-Point Diamond Turning Lathe

I. Core Principle

• Cutting Tool: Natural single-crystal diamond tools are used, with an extremely small nose radius (typically 0.5–1 mm, and cutting edge below 50 nm), ultra-high hardness and excellent wear resistance.
• Machine Tool: Ultra-precision CNC lathes equipped with air-bearing / fluid-bearing spindles, air-bearing guideways, and closed-loop feedback via laser interferometers, achieving nanometer-level positioning accuracy.
• Process:
  1. Input the mathematical equations of aspherical surfaces (such as parabolic surfaces, hyperbolic surfaces, high-order aspherical surfaces) into the CNC system.
  2. The machine tool controls the workpiece to rotate at high speed, while the cutter performs two-axis linkage in the radial (X-axis) and axial (Z-axis) directions to conduct micro-cutting at the micrometer / sub-micrometer level.
  3. The single-point contact between the cutter and the material directly turns a complete aspherical curved surface in one forming process.

II. Key Advantages (Why Choose It for Aspherical Surfaces)

• Ultra-high precision

  • Surface form accuracy (PV): down to below 0.1 μm (even λ/20, λ=632.8 nm).
  • Surface roughness (Ra): 1–5 nm, close to mirror finish, generally requiring no polishing.

• Strong capability for complex curved surfacesCapable of directly machining aspherical surfaces, off-axis aspherical surfaces, free-form surfaces, and diffractive surfaces, realizing complex shapes difficult to achieve with traditional grinding.

• High efficiency and good consistencyOne-step forming replaces the traditional multi-process workflow of "rough grinding → fine grinding → polishing", greatly shortening machining time.Extremely small surface form deviation of batch parts (e.g., < 0.15 μm), suitable for high-end small-batch production.

III. Applicable Materials

• Non-ferrous metals: Aluminum, oxygen-free copper, brass, electroless nickel-phosphorus alloy (most commonly used).
• Infrared crystals: Germanium (Ge), Silicon (Si), Zinc Selenide (ZnSe), Zinc Sulfide (ZnS), Magnesium Fluoride.
• Plastic materials: Selected optical plastics (PMMA, PC), epoxy resin.
• Not applicable: Ferrous metals such as steel (carbon diffuses at high temperatures, causing rapid tool wear).

IV. Typical Applications (Aspherical Field)

• Infrared optics: Aspherical lenses / mirrors for thermal imagers, night vision devices, and LiDAR.
• Photography / Security: Aspherical lenses for large-aperture prime lenses and high-pixel surveillance cameras.
• Aerospace: Aspherical optical systems for satellite remote sensing, astronomical telescopes, and missile seekers.
• Medical / Scientific Research: Micro aspherical lenses for endoscopes, laser focusing lenses, and optical components for fluorescence microscopes.
• Consumer Electronics: Ultra-thin aspherical lenses for smartphone cameras and VR/AR devices.

V. Machining Key Points (Ensuring Aspherical Precision)

• Environmental control: Constant temperature (±0.1°C), constant humidity, ultra-cleanliness, and active vibration isolation (temperature variations severely affect surface form).
• Tool compensation: Precise compensation for tool radius, wear, and installation errors.
• Path optimization: Reduced feed rate and cutting depth in high-steepness areas; avoiding interference of the tool clearance angle.
• Error compensation: Online measurement and compensation of spindle errors, machine tool geometric errors, and material deformation.

VI. Summary

Single-point diamond turning (SPDT) is the "gold standard" for aspherical manufacturing:

• Advantages: Nanometer-level surface quality, sub-micrometer-level surface form, complex curved surfaces, one-step forming, and high consistency.
• Positioning: The preferred process for high-end, small-batch, high-precision aspherical components.