CASE STUDY: Ultrasonic Productivity

November 1, 2007
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ASML Optics has found success with a new approach for glass ceramic composite machining that provides fast material removal while maintaining superior accuracy.

Zerodur block shown before (left) and during an ultrasonic glass machining process.

ASML Optics Group, Richmond, Calif., has significantly improved its productivity through the use of ultrasonic machining on various glass ceramic composites, including Zerodur®.* The company’s advanced facility supplies its parent company, ASML, Veldhoven, the Netherlands, with a variety of components used in advanced systems and equipment builds for the semiconductor industry, including wafer stepper and scanner machines.

Zerodur is an expensive raw material that features the necessary properties (including extremely low thermal expansion, outstanding homogeneity and excellent processing characteristics) required by the high-accuracy applications of the semiconductor industry. The machinery produced by ASML is used 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 ASML Optics must therefore attain consistently uniform tolerances of less than 10 microns.

ASML Optics 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 provide fast material removal while maintaining superior accuracy.

*Zerodur is a registered trademark of Schott AG.

ULTRASONIC 50 with machine travel (XYZ) of 500 x 450 x 400 mm, features an HSK 63-S tool fitting that permits ultrasonic and conventional milling on a single three-axis machine.

Finding the Right Tools

ASML Optics reviewed numerous technologies and other ultrasonic machine tool suppliers before deciding on the ULTRASONIC 50 and ULTRASONIC 70, two machines from DMG America, Inc. that offer the flexibility for three- and five-axis machining in both ultrasonic and conventional milling machine modes. The Siemens SINUMERIK 840D CNC, which features the capability for quick programming and setup in either machining mode, is included on each of the machines.

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 (as well as the status of the coolant pressure) via an electrical echo signal. Special HSK 63-S tool fittings on the DMG machines further enable the changeover from conventional milling to ultrasonic machining mode.

In DMG ultrasonic machining technology, the machining spindle creates 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 Erich Bertsche, DMG’s national product manager, the permanent gap between the tool and the workpiece leads to a significant reduction in the heat stress and work force required, thus conserving the tool life and the workpiece’s material integrity.

An inductive spool that functions as the transmitter is affixed to the tool interface beneath the spindle head. Another spool on the HSK 63-S fitting functions as the receiver. As a result of the ultrasonic stimulation, the diamond tool kernels contact the workpiece surface with a controlled force, thereby 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, holding extremely tight dimensions with surface finishes to 0.2 µm (0.000008 in.) or better.

 “Our group works in various advanced material compositions,” says Matthew White, ASML Optics manufacturing manager. “The challenges of Zerodur, as well as others, required 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 to the DMG ULTRASONIC machines and continue to find new and better ways to use them for the improvement of our overall process here at ASML. This machine tool supplier also provides us with the special tooling needed to machine Zerodur.”

DMG uses a special Sauer galvanizing and sintering process to create the diamond tools for ultrasonic machining. The key factor in diamond tool production, as with all machining tools, is to maintain balance in the machining of materials. The Sauer process of integrating galvanized tool steel for strength with the sintering of the diamond kernels maintains a uniformity in the final product, whether it is an endmill or surface, perimeter or profile grinding tool.  Through this process, a unique binding matrix keeps the diamond kernels precisely in place during continuous tool oscillation.

Siemens SINUMERIK 840D CNC with its open architecture allows easy programming and setup for either ultrasonic or conventional milling work.

Simple Programming

ASML Optics performs its own programming on the ultrasonic machines using the Swivel Cycle Siemens machine control technology. “We set up the origin of the part and the Swivel Cycle allows for rotational shift of the coordinate system and XYZ transitional, with no separate work offsets needed,” explains White. “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 is incredible.”

As part of the Siemens ShopMill suite, the Swivel Cycle has a menu-driven feeler function for determining the zero-point offset, even in swiveled five-axis machining planes. It allows flexible input of the swivel angles in a workpiece coordinated system, including axis angle, solid angle and angle of projection. Thus, both the programming and the setup time are significantly reduced. For a job with numerous one-off or small batches made from extremely costly materials, this feature further expands job potential while substantially speeding up throughput.

The cooperation between DMG and the Siemens team in developing the HMI has resulted in faster training on the machines through the use of standard M-code actuation of the ultrasonic on/off, standard ISO code, and the onboard Adaptive and Acoustic Control programs. The DMG setup of all parameters is done seamlessly as another window within the standard Siemens CNC screen array.

The concept of open architecture on the SINUMERIK 840D CNC enables the machine builder to program its own functionality into the NC kernel. This design in the CNC supports the customer with more flexibility in setup strategies, as well as faster cycle and reaction times. Since the machining process is continuously monitored, unattended machining is possible, even for high-precision, small batch runs.

For example, intelligent control algorithms typically regulate the feed rate while machining an inside radius. Process force usually increases, even if the other parameters remain static, owing to the high angle of content. The Siemens control recognizes these contours and automatically adjusts the feed rate to maintain the correct cutting conditions. Also, with the touch of a button, an ASML Optics operator can call up the ultrasonic generator screen and all variables can be quickly adjusted, including ultrasonic frequency, amplitude and output, or the operator can automatically adjust the output for a defined number of tools in the automatic tool changer (ATC).

Widespread Benefits

In addition to the semiconductor manufacturing equipment sector, the ULTRASONIC series of machines also produces parts made from advanced composites and other non-conductive materials for the brake, aerospace, optics and medical/orthopedic market segments.

The new system has been an unqualified success at ASML Optics. “The significant improvement in the shop’s productivity stems from the recent addition of the new ultrasonic machining equipment supplied by DMG America,” says White. “These machines have ramped up our productivity by a factor of five compared to the previous technology we utilized.”

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