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components—linear and rotary stages—
bolted together.
“We looked at that platform a few years
ago and found that a fundamental limitation
on increasing processing speeds was
the stiffness of the system,” said Rekowski.
As a result, Aerotech incorporated into
its VascuLathe laser motion machine an
integrated linear-rotary design capable of
providing throughput two to five times
greater than component systems, while
still providing micron-level dynamic
tolerances.
“The stent struts could be on the
order of 70μm wide, and they might
have features with a radius of 20μm,” said
Rekowski. “With features of this size, it is
critical to track part geometry very precisely
[because] overshooting into a corner
can undercut a strut and reduce its
yield strength.
Aerotech has also improved its motion
control software, according to Rekowski.
“We can allow customers to program one
global feed rate for the part they’re running,”
he said. “The controller automatically
slows down when it comes across
geometries with extremely small features.”
For example, if the radii of a part’s diameter
decrease, the program automatically
decreases the feed rate and, in turn,
increases it on long, straight sections of
the stent. “Our software can now handle
all that optimization directly; we remove
that from the customer’s responsibility,”
Rekowski said.
Laser innovations
Cleveland-based Norman Noble Inc.’s
unveiling last September of its UltraLight
athermal laser—capable of machining
metals and polymers without risk of producing
heat-affected zones or burns—
provided the latest example of evolving
laser machining technology. News of
UltraLight arrived as the stent industry
was largely migrating from YAG lasers
to the more-precise fiber lasers.
“When stent manufacturing started
more than 10 years ago, the standard tool
was the lamp-pumped Neodium YAG
laser with a wavelength of 1,064nm,” said
Rofin Sinar’s Quandt. “But during the past
few years, users have been adopting the
fiber laser as the standard laser due to its
high beam quality and higher frequency.
Cutting speeds up to twice as fast [as
the previoius technology] are achieved,
Raydiance
A bioabsorabel stent, with 80µm-dia. struts, machined with
the Raydiance SmartLight MD50 laser.
resulting in higher throughput. Also,
finer cuts can be achieved—for example,
a 0.0006" cut width in materials with
100μm-wall thickness. In the coronary
stent field, the 20μm to 25μm cut was
standard with the lamp-pumped YAGs,
but with the fiber laser, it’s possible to cut
a similar stent with a narrower cut width.”
Compared to YAGs, fiber lasers are
up to 30 percent more energy-efficient.
Also, fiber lasers typically require new
lamps every 50,000 hours compared to
every 500 hours for YAGs,
so their maintenance needs
are lower.
As with YAG lasers, standard
fiber lasers also produce
a heat-affected zone
(HAZ) on stents. “There are
ways to limit the laser heat
input into the materials; for
example, when pulsing the
laser, you would reduce the
cut width or pump a liquid
through the tube material
during the process,” said
Quandt. “However, there’s
always some HAZ, which
means that a laser-cut metal stent always
requires post processing (chemical etching
and electropolishing).”
But since Norman Noble’s new Ultra-
Light femtosecond laser cuts material
without producing a HAZ, post-processing,
save for electropolishing, is a
non-issue. The UltraLight incorporates
the SmartLight MD50 femtosecond fiber
laser introduced last year by Raydiance
Inc., Petaluma, Calif. The SmartLight
(50-microjewel-per-pulse) system cuts
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