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Ruled Insert with minima wave-form
These ruled- inserts, made of hardened steel, optimizing the imaging characteristic of the molded optical surface by minimizing color separation thereby improving the vitality of the image displayed. They were produced by diamond turning a pair of inserts, one with concave and the other convex profile (of mirror image) and subsequently matched together by these surfaces and honed with each other by rotating them at differential speed. Such action with appropriate speed and lubricating setting, enable the reduction of the waviness to a minimum on the diamond cut surfaces.
This picture illustrates a couple of spherical (R 70mm) ruled-inserts with radius deviation of 0.015%; surface finish < 5nm. The size of the square insert is 10×10 mm whilst the round ones is 19 mm diameter.
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Benefit: Direct Cut Steel Technologies
Steel is one of the most popular engineering materials used in industries. However, cutting steel directly with a diamond cutter causes severe tool wear. Various approaches have been investigated to improve the tool life and surface finish of the work piece. This includes cryogenic cooling, application of carbon-rich gas and ultrasonic vibration assisted machining.
We had successfully overcome this difficulty by development of a vibration assisted single-point diamond cutting module. It increased the cutting efficiency and surface finish of bare steel-alloy substrate, enabling its application for generating optical profile of mirror finish on hardened steel when attached on an ultra precision machine.
Hardened stainless steel work piece sizes from less than 1 mm to greater than 40mm in diameter have been machined using this method and a finish of better than 5 nm Ra can be obtained. A profile accuracy of 0.15μm had been achieved for 10mm diameter samples. It has bee used to produce numerous pieces of optical inserts for plastic lens molding applications
The advantages of diamond direct cut steel inserts over nickel plated ones:
- Shorter fabrication turn-around time (one week versus 4 weeks)
- Better quality surface (high scratch resistance, less peeling, no chipping/cracking on sharp edges, less prone to tarnishing, etc)
- Longer mold life (at least 3 times over nickel plated ones) & no DE-laminating of plating
- Higher molding temperature (over 300°C)
