Diamonds may be a girl’s best friend, but are they the lens manufacturer’s best friend? Perhaps not, as the Sumitomo and Mono Die crystals now offer a real alternative to the natural diamond. Most manufacturers know not much about these synthetic crystals and so it is not surprising that when a synthetic crystal tool is suggested for a specific application, it is met with apprehension and doubt. A better understanding of these new materials for cutting tools may be useful and help in selecting the best type of tool for specific cutting requirements.

Originally manufactured as a diamond heat sink material, the Sumitomo and Mono Die crystals were pure and had increased nitrogen content. With this in mind, Contour Fine Tooling received the first samples of this material in 1986. Tools were made and sent out to selected customers for trials. The initial reaction was very favourable but manufacturing tools with these crystals proved to be difficult due to their inconsistency. It took over two years of collaborating with the manufacturers before Contour was able to receive a supply of consistent crystal suitable for its demanding requirement for cutting tool manufacture.

Further tests were conducted on various materials, using crystals that were rigorously inspected, especially for orientation alignment, which is one of the most critical factors in tool performance. Results were promising with reports from the evaluating companies who started ordering these crystal tools. Contour began a systematic programme of evaluating the performance on various types of materials-from contact lens blanks to various metals. Notable differences were seen when using synthetic crystals on certain materials as compared to natural diamonds.

With materials that are prone to chemically wear natural diamonds such as RGP materials, synthetic crystal tools perform better and resist wear longer. On soft lens materials, natural diamonds are the first choice. With PMMA, particularly for IOL manufacture, a 0.25mm natural diamond is usually the best combination.

More and more cutting tools are being manufactured and used to cut metal moulds for the production of moulded lenses. It is advantageous for the mould manufacturer to use the best lathes and the best cutting tools, avoiding cutting lines and polishing as much as possible. In this application, low waviness conical natural diamond tools are distinctively better.

What about cutting complex geometries, such as torics, multifocals, keratoconus lenses? Does the material make the most difference, is it the shape of the tool or is it synthetic vs. natural diamond? From Contour’s point of view and experience, the material usually determines the type and geometry of the tool that is used. As stated above, RGP materials will wear out a natural diamond much quicker than a synthetic crystal.

How does the synthetic crystal behave differently from the natural diamond tool? Initially, the surface finish on the work piece deteriorates at a similar rate as a natural diamond. The synthetic crystal tool will hold this finish over a long time, but will deteriorate quickly to a poor finish. This will make it obvious for a tool change. Natural diamond tools have a different characteristic in that they show progressive and continuous wear rate throughout their life.

Contour’s on site technical support as well as the applications support teams in all four Contour manufacturing sites are available to review your applications and needs, and to work together to help select the right tool – Natural or Synthetic.