May 2007 Edition
Machining
Ultrasonic Machining Found to be a Sound Idea
When machining one of the world’s most expensive materials, there’s no room for mistakes
Through the use of ultrasonic machining on various glass
ceramic composites, including Zerodur, the ASML Optics
Group, Richmond, CA, improved its productivity. The firm
supplies its parent company, ASML, Veldhoven, The Netherlands,
with components used in systems and equipment for
the semiconductor industry.
“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 10μ.
Better Machining While Maintaining Tolerances
ASML has been machining glass
materials for years, but concluded that
it needed to increase its productivity
without sacrifi cing 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 diffi culty 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 powerline
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.
Oscillation
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 fi ve 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 fi tting 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 0.2μm – 0.000008" – or better.
One-off is the standard at RER, with
a typical workpiece starting as a 600 lb
billet and finishing as a 400 lb machined
shaft.
With the look-ahead feature of the Siemens
CNC, the Weiler control maintains
a constant cutting speed, while adjusting
for angle-to-radius changes, especially
on precise internal threading.
Substantial Upsides
“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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