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TECHNOLOGY BACKGROUND

Dr. Liu Xiang Dong has been leading the development programs of ultra-precision machining technologies since 1996 in SIMTech. He had successful developed an DSCD system which had practically enable the “direct-cutting” of steel to mirror surface finish by a diamond tool, thereby eliminated the need of nickel coating on the optical inserts made of steel as usually does. Such inserts produced by the direct-cutting method have a much higher scratching resistance, have no porosity in their microstructure and do not subject to surface peeling during molding. Further, the molding life of the inserts with no nickel coating last three time longer than the coated ones (subjecting to the same operating parameters). Figure 1 illustrates optical inserts produced by DSCD.


Figure 1. - Photo of DSCD machined Mirror Surface Finish Aspheric
Cavity Optical Inserts made of hardened Stavax (HRc 52)

The capability to produce uncoated steel inserts with diamond turning technology opens new application possibility for plastic lens molding. Since the uncoated steel inserts do not suffer from the differential thermal expansion as the nickel coated ones, therefore they could be operated at relatively higher molding temperature which is necessary for the processing of some plastic materials used for high performance optics.

This technology has greatly reduced the one-month fabrication duration of these inserts (which normally includes process sequences to semi-finish optical profile, electroless nickel coating, grinding OD to remove excess nickel coating and finish optical profile of the inserts) to one day. The DSCD system only needs two steps – semi-finished and finished machining to complete the optical profile of the inserts. A shorter lead-time will definitely enhance the competitiveness of plastic lens and optical component molders.

DSCD have been used extensively to fabricate over thousand pieces of uncoated steel inserts from year 2002 for the local and regional plastic lenses and optical components molding companies. The profile accuracy and surface finish of these inserts produced by DSCD have been measured and the results are illustrated in the charts on the following


Figure 2. – Surface roughness topography (Ra 7.41 nm) of an Aspheric
Optical Insert measured using Wyko Interferometer
Figure 3.- Profile Accuracy (within 0.1 µm) of an Aspheric Optical
Insert measured with a Tylor Hobson Profilometer

A few years ago, the manufacturing of plastic optics using injection molding could only be done in the USA, Europe and Japan. This was due to the lack of ultra-precision machining capability to produce the optical mold inserts, the key element in the injection molding of plastic optics. The know-how and technologies developed in ultra-precision machining by Dr. Liu had since made a very remarkable impact in the commercial application of plastic lens and
optical component molding in this region.

These achievements places the company in a leading position in the fabrication of optical mold inserts internationally. Till date Delta Optics Technologies is the only company that has successfully applied the technology to cut steel directly with diamond tool for industry practices in the manufacturing of plastic and optical components for mass production programs of devices for the vast consumer markets.

Delta Optics Technologies has developed methodology to compensate shrinkage error of the plastic optics which occurs during the solidification/cooling stages of the molding process has in a typical case improved the form accuracy of the molded plastic lens from 25 to 1.5 microns. It is achieved by modifying the mold inserts such that they improve the accuracy of the molded plastic optics. The profile offsetting approach enhanced the quality and molding process control and therefore increased yield of the process.

Delta Optics Technologies is a company spun off from Singapore Institute of Manufacturing Technology (SIMTech) to better support the optical & molding industries with states-of-the-art technologies to produce mirror surface finish better than 8 nm Ra on steel with hardness above HRC50. We are the only commercial company having such capabilities in the world where thousands of pieces of hardened steel optical mold inserts have been manufactured with this technology.


 

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