Apple notes that sapphire is a hard material with a hardness of 9.0 on the Mohs scale, making it an attractive alternative to glass or polycarbonate. However, it's also very brittle, and susceptible to dramatic strength reductions if there are small defects in the surface or edge.
Manufacturing a near defect-free sapphire part may present unique challenges. The strength of a brittle material, such as sapphire, is limited due to flaw population on the surface or edges of the part. An inconsistent or inadequate surface or edge finish can lead to the propagation of micro cracks and result in a weakened part. Traditional translucent materials like silicate glass are able to be chemically strengthened to a significant depth to minimize the effect of these flaws, but on extremely hard materials such as sapphire, a similar process is not readily available. Additionally, sapphire's hardness makes cutting and polishing the material both difficult and time consuming when conventional processing techniques are implemented. Further, conventional processing tools, such as cutters, experience relatively rapid wear when used on sapphire. This further increases the resource demand when surface finishing sapphire parts.
To minimize the micro-defects, Apple has devised a system and method for producing high-quality edge cuts in a rapid, repeatable fashion using a laser cutting process that uses more than one gas medium to help remove material and also control discoloring that may occur during the cutting process.
In particular, a fusion laser cutting process can be used to produce a sapphire part having acceptable edge and surface finish. During a fusion cut, a laser beam is used to heat and partially melt a portion of the sapphire material. A directed stream of gas is then used to remove the melted material leaving a void or depression in the sapphire material. The efficiency and edge finish produced by a fusion cut may be superior to other types of laser cutting techniques, including, for example, ablation laser cutting techniques or laser scribing.
Although, Apple is using sapphire glass for the Apple Watch, it's unclear if the company will be able to obtain sufficient quantities and yields to bring a sapphire glass display cover to the iPhone in the near future. It's previous attempt to produce sapphire with GT Advanced ended horribly and we've yet to hear any substantial rumors about a new supplier taking GT's place.
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Read More [via CultofMac]