Polycrystalline diamonds and technical ceramics are extremely wear-resistant. However, this advantage is actually a disadvantage when it comes to processing these materials. Laser methods provide a remedy.
The growing variety of materials pose certain challenges for material processors. To cut, drill and structure aluminum and magnesium alloys, composite materials, hard metal alloys and plastics containing metal particles requires extremely abrasion and wear-resistant tool materials. The means of choice are often synthetically manufactured polycrystalline diamonds (PCD) and technical ceramics. In addition to having maximum abrasion and wear resistance, these ultra-hard materials have further advantages, such as low thermal expansion and corrosion resistance. These days, these materials ensure continuous precision and reliability in tools while also protecting highly stressed surfaces in bearings, pumps and motors against wear and tear. And since they are biocompatible, there is also increasing demand for the high-performance ceramics in medical engineering.
However, along with the benefits of PCD and technical ceramics for manufacturers of tools, pumps and bearings, there is also the question of how these materials can be processed without themselves causing extreme wear on the tools required to shape them. The answer is: Light. For example, II-VI Inc recently presented a laser lapping system developed especially to process PCD and ultrahard ceramic materials. According to II-VI, this laser-supported precision machining method is twice as efficient and less prone to errors than the existing electrical discharge machining (EDM) used for PCD and ceramics. At the heart of the new lapping system is an air-cooled 450-watt fiber laser with 1060 nm wavelength.
Ultrashort pulses and water-jet guided laser processes
Laser processing of high-performance ceramics is also a focus at Fraunhofer ILT in Aachen and at Pulsar Photonics, an ILT spin-off established in 2013. Scientists at ILT and the Pulsar team use ultrashort pulse (USP) technology to prevent micro cracks and spalling when the brittle materials are being processed. With the help of pico and femtosecond lasers, they create tiny holes, structures and cuts in technical ceramics, such as silicon nitride, aluminum and zirconium oxide and titanium dioxide. Although the materials are extremely hard, the contactless processing is virtually wear-free. ILT says that the picosecond laser pulses are very productive—from both material removal rate and the quality of the ceramic processing aspects.
As an alternative to USP methods, Swiss specialist Synova uses an in-house-developed Laser MicroJet (LMJ) method to process polycrystalline and monocrystalline diamonds (PCD, MCD). In these LMJ systems, more than 350 of which already have been shipped around the world, the laser beam is focused into a nozzle while passing through a pressurized water chamber where it is coupled in a 50-micrometer water jet. Like an optical fiber, the water jet holds the laser beam captive on its way to the workpiece. Synova explains the phenomenon with the total internal reflection at the transition zone between water and air. When they collide with the PCD or MCD layers, the 25 to 30-watt laser pulses evaporate the material, while the water cools the material and washes away any ablated material from the processing area. The cylindrical laser beam constantly tunnels its way into the precious stone’s structure—even several centimeters deep if required. The LMJ is used not only for technical diamonds, but also to process raw diamonds, rhinestones and other jewels. Here, too, contactless laser processing produces optimum results with minimum wear.