Ultrasonic machining found to be a sound idea: when machining one of the world's most expensive materials, there's no room for mistakes.
"The significant improvement in the shop's productivity stems from the ultrasonic machining equipment supplied by DMG America," Matthew White, ASML Optics manufacturing manager, said.
Zerodur is an expensive raw material with the necessary properties required by the high-accuracy applications of the semiconductor industry. The machinery produced by ASML is used by semiconductor manufacturers in 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. The parts produced from Zerodur by ASML must attain uniform tolerances of less than 10[micro].
Better Machining While Maintaining Tolerances
ASML has been machining glass materials for years, but concluded that it needed to increase its productivity without sacrificing tight tolerances. Often, the prototyping process at this facility leads to a production run, once the prototype has been found suitable for the application. Given the difficulty in machining Zerodur, a new approach was required that would render fast material removal while maintaining accuracy.
The company reviewed numerous technologies and other ultrasonic machine tool suppliers before selecting the Ultrasonic 50 and Ultrasonic 70, two machines from DMG, Schaumburg, IL, that offered the flexibility of 3-axis and 5-axis machining in both ultrasonic and conventional milling machine modes.
Onboard each of these machine tools is the Siemens Sinumerik 840D power-line CNC for quick programming and setup in either mode. In ultrasonic mode, the Adaptive Control and Acoustic Control monitors the machining action and adjusts the feed and spindle speeds to maintain accuracies at the desired levels.
Adaptive Control monitors the process forces of 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 machines enable the changeover from conventional milling to ultrasonic machining mode.
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. 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 Erich Bertsche, DMG national product manager, the permanent gap between the tool and the workpiece leads to significant reduction in the heat stress and forces, conserving tool life and the workpiece 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 is another spool that functions as the receiver. As a result of the ultrasonic stimulation, the diamond tool kernels contact the workpiece surface with a controlled force, removing the material in a precise and predictable manner.
In the semiconductor industry, this machining technique is frequently used to work silicon, silicon carbide, silica glass, and glass-ceramic composites such as Zerodur, holding dimensions with surface finish to 0.2[micro]m--0.000008"--or better.
"Our group works in advanced material compositions," Matthew White of ASML, said. "The challenges of Zerodur, as well as other material, require us to look for a new machining strategy to maintain our manufacturing standards, while continuing to supply our parent company with the necessary part production.
"We saw substantial upsides with the machines and continue to find new and better ways to use them for the improvement of our overall process here at ASML. We have ramped-up our productivity by a factor of five, compared to the technology we used."
ASML programs its ultrasonic machines, taking advantage of the Swivel Cycle unique to the machines' Siemens controls.
"We set up the origin of the part and the Swivel Cycle allows for rotational shift of the coordinate system, XYZ transitional, with no separate work offsets needed," White said. "Where once we needed four setups over three machines, we can now perform two setups on one chuck on one DMG machine. The time savings are incredible." Siemens Energy & Automation, Machine Tool Business
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|Publication:||Modern Applications News|
|Article Type:||Cover story|
|Date:||May 1, 2007|
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