Areal Surface Texture Parameter Measurement in Micro Injection Mould Cavities
Areal surface metrology in micro-cavities requires non-contact optical instruments with matched bandwidth filters to verify steel texture and polymer replication.
Diamond Turning Surface Texture
Meaning
Nanometer-scale surface finish produced by a high-precision machining process uses single-crystal diamond cutting tools on non-ferrous metals or polymers. In optical moulding, diamond turning surface texture determines the light transmission and scattering properties of the moulded lenses or light guides. This process achieves sub-micron form accuracy and surface roughness in the range of a few nanometers, eliminating the need for post-mould polishing.
However, the tool path leaves microscopic spiral grooves that can act as a diffraction grating if the machining parameters are not optimized, which can degrade the focus of the moulded lens.
Optical Performance
Microscopic grooves from the turning operation affect how light interacts with the moulded polymer surface. When moulding optical components with polymethyl methacrylate or cyclic olefin copolymer, the replication of these fine lines can cause unwanted light dispersion. Moulders must verify the surface texture of both the steel inserts and the moulded parts to ensure that the diffraction effects do not compromise the optical clarity of the system.
Wear Rate
Tooling inserts made of nickel-phosphorus or copper are typically used because steel degrades the diamond tool rapidly. While these softer metals allow for a highly refined diamond turning surface texture, they are susceptible to wear during long production runs, especially when moulding abrasive or glass-filled resins. Sourcing hard coatings can protect the fine details but may alter the final roughness.
Measurement Limit
Standard contact styluses cannot accurately resolve the extremely fine peaks and valleys produced by this precision machining. Metrology of the diamond turning surface texture requires non-contact optical techniques like coherence scanning interferometry. This measurement confirms that the nanometer-scale roughness conforms to the design specifications before the insert is used in the injection press.