By Christoph Ruettimann, Noémie Dury and Markus Danner
With almost 40 years of experience in precision processing of synthetic crystalline materials, Swiss laser manufacturer ROFIN-LASAG AG has developed a process for cutting sapphire glass, which is now increasingly used in mobile electronic devices and high-quality mechanical watches. Synthetic sapphire is a mono-crystalline aluminum oxide with outstanding technical properties, such as a high thermal conductivity, very high light transmission and complete acid resistance. In addition, it is an outstanding electric insulator and extremely scratch-resistant: With a Mohs’ hardness of 9 sapphire is beaten only by diamond.
Sapphire can be cut with a variety of laser technologies. Ultrashort pulse lasers, such as picosecond lasers, cut the material using very short pulses. The energy of these pulses is transferred so quickly to the electrons that the chemical bonds of the atoms are destroyed. In contrast to that, pulsed fiber lasers with a pulse length in the range of microseconds to milliseconds work with another cutting process, so-called fusion cutting. The material to be cut is fused at the focal point and blown out of the cutting kerf using a high-pressure process gas. The precise control of the energy input through the pulse length, the pulse shape, and the frequency in combination with the cutting speed are decisive. Despite the thermal fusion, no microcracks should occur and, ideally, no blow-outs of the edges either.
The parameters, processing heads and laser sources developed with pulsed fiber laser by ROFIN-LASAG AG allow for a considerably higher cutting speed than ultrashort pulse laser when processing sapphire depending on the material thickness, and this for a fraction of the investment costs. A system solution for the complete processing of sapphire is made from a total of four basic elements: the laser source, the processing head including optical elements and the beam guide, the tailored process developed for the cutting of sapphire, and the machining center.
Consistent with pulsed fiber lasers, which are characterized by their high beam quality, ROFIN-LASAG AG has developed a multiple processing head, which makes it possible to cut several components at the same time with a single beam source. The use of a multiple processing head creates massive savings, especially in CNC machining centers: the capacity can be multiplied with a slightly higher investment volume.
To achieve the maximum processing speed with the highest precisions on the machines, a solid machine base is required. This must reliably absorb the dynamic forces that arise without vibrating. Depending on the cut geometry and cycle time, ultra-dynamic axes are used, and the inertia of the machining table is minimized. As a result, the smallest curve radii and sharp corners can be achieved without overshooting.
Alongside the success of sapphire, ROFIN-LASAG AG is developing and optimizing its processes in line with the market, so that it will continue to be one of the most innovative and leading international laser manufacturers in the future.