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Zerodur is a glass ceramic that's one of the most expensive materials around, so getting it right the first and every time it's cut is critical. Through the use of ultrasonic machining on various glass ceramic composites, including Zerodur, the ASML Optics group in Richmond, California has significantly improved its productivity.
This highly advanced facility supplies the parent company, ASML in Veldhoven, The Netherlands, with a variety of components used in its advanced systems and equipment builds for the semiconductor industry, including wafer stepper and scanner machines.
"The significant improvement in the shop's productivity stems from the recent on streaming of new ultrasonic machining equipment supplied by DMG
America of Schaumburg, Illinois," said Matthew White, ASML Optics
manufacturing manager.
Zerodur is an extremely expensive raw material with the necessary properties required by the high-accuracy applications of the semiconductor industry. The machinery produced by ASML is utilized by semiconductor manufacturers in their critical lithography operations to image circuit patterns in photoresist on silicon wafers in the chip production process.
A new ASML technology, TwinScan, images one wafer while simultaneously measuring the next one. The parts produced from Zerodur by the ASML Optics Group, therefore, must attain consistently uniform tolerances, less than 10 microns.
ASML has been machining glass materials for years, but concluded that it needed to increase its productivity without sacrificing the extremely tight tolerances held in its machining processes. Often, the prototyping process at this facility leads quickly to a production run, once the prototype has been found suitable for the application. Given the difficulty in machining Zerodur, an entirely new approach was required, that would render fast material removal while maintaining superior accuracy.
Figure 1: The Ultrasonic 50 from DMG, with machine travel (XYZ) of 500mm x 450mm x 400mm, can do ultrasonic and conventional milling on a single three-axis machine.
The ASML Optics group reviewed numerous technologies and other ultrasonic machine tool suppliers before deciding upon the Ultrasonic 50 and Ultrasonic 70, two machines in the DMG series that offered the flexibility for three-axis and five-axis machining, in both ultrasonic and conventional milling machine modes.
Onboard each of these machine tools is the Siemens Sinumerik
840D powerline CNC that has the capability for quick programming and set-up in either machining mode. In the ultrasonic mode, the Adaptive Control and Acoustic Control features of the CNC combine with its open architecture design to effectively monitor the machining action and quickly adjust the feed and spindle speeds to maintain predictable accuracies to the desired levels of this demanding customer environment.
Adaptive Control monitors the process forces on the machining tool, while the Acoustic Control registers the intensity of the tool vibration on the workpiece surface via an electrical echo signal, as well as the status of the coolant pressure. Special HSK 63-S tool fittings on the DMG machines further enable the changeover from conventional milling to ultrasonic machining mode.
Figure 2: Siemens SINUMERIK 840D powerline CNC allows easy programming and set-up for either ultrasonic or conventional milling work. In ultrasonic mode, the Adaptive Control and Acoustic Control features automatically adjust the feed and spindle velocities during machining.
DMG ultrasonic machining technology involves the machining spindle creating an oscillation that causes the diamond tool to pulse with a controlled frequency between 17,500 and 48,000 times per second, depending on the spindle type used. This action removes micro-particles from the material surface, at a rate approximately five times that of conventional machining, especially on such advanced composite materials as Zerodur.
According to DMG national product manager, Erich Bertsche, the permanent gap between the tool and the work piece leads to significant reduction in the heat stress and the work force required, thus conserving the tool life and the work piece material integrity. An inductive spool that functions as the transmitter is affixed to the tool interface underneath the spindle head. On the HSK 63-S fitting itself is another spool that functions as the receiver.
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