By Geoff Shannon and David Van de Wall
Many adults are old enough to remember a time when heart problems were a death sentence. Thankfully, times have changed.
Today a small device such as a stent (see Figure
1), which is placed in an artery as part of a coronary
angioplasty surgery and helps to restore blood flow
through damaged arteries, can mean a new lease on
life. With the growth of minimally invasive surgery,
the medical community has an incredible need for
these kinds of laser-cut stents and flexible tubing.
While legacy stent and tube cutting systems have
performed well during recent decades, new cutting
technologies coming onto the market offer faster
and better cuts, with higher production rates and
new and unique cutting capabilities.
Replacing Legacy Cutting Systems
The pulsed neodymium-doped yttrium aluminum
garnet (Nd:YAG) lasers used in the past two decades
have definitely been great workhorses. Unfortunately, the original pulsed Nd:YAG lasers that remain
in operation can’t match new laser capabilities and
are increasingly difficult to service. While many of
these systems have been upgraded to fiber lasers,
they are still beset with older support systems and
slow and aging controllers with legacy software.
Simply put, the laser, mechanicals, controller, software, water systems, and automated tube
loader technology have all moved on. All of these
components contribute to better cuts with higher
production rates and less downtime.
Laser. The pulsed Nd:YAG lasers used in the past
have been superseded by fiber lasers with better
beam quality that does not change with pulse ener-
gy and average power. This beam provides a smaller
and more consistent focused spot size, which re-
sults in tighter cutting tolerances and, with spot siz-
es down to 10 microns, the ability to cut much finer
detail features. These lasers provide pulse frequen-
cies over 5 kilohertz and pulse widths down to 20
microseconds to enable energy input optimization
for a variety of tube materials and wall thicknesses.
Higher frequencies can be used to maximize acceleration and speed for a range of part thicknesses.
From an operational standpoint, fiber lasers have
a number of advantages. They are air-cooled, run
off single-phase 240-volt electrical power, and have
diodes with lifetimes that are greater than 70,000
hours. Figure 2 shows an example of a tube produced by new laser tube cutting technology and a
close-up of laser tube cutting.
Fiber lasers use microsecond pulses and have a
cutting speed and edge quality that are sufficient
for many applications. The femtosecond laser offers laser pulses that are under 400 x 10-15 seconds,
or about 1 million times shorter than the fiber laser. The very short pulse duration, combined with
peak powers into the gigawatt level, allows special
cutting capability. The fiber laser has a fusion cutting mechanism, whereby the laser pulse melts the
metal, which is then ejected from the part by a coaxial high-pressure gas. The very high peak power of
the femtosecond laser and a pulse duration that is
shorter than the material’s conduction time create
a very nearly pure vaporization mechanism. Since
there is no melt creation during the cutting process,
there is no burr, which is very beneficial for such
materials as nitinol.
Take the example of the ubiquitous coronary
stent, one of the first devices manufactured with
both Nd:YAG and fiber lasers. First, the part has to
be machined, honed, or cleaned on the inside with a
mechanical tool and finally deburred. Then a chemical etch process must be performed to clean up
around the edges, followed by an electropolishing
step. These steps are quite time-consuming. They
also can cause the part to become brittle or deformed and may result in microcracks. Yields tend
to be in the 70 percent range, which means the loss
of a considerable amount of end product, which can
be a significant material cost in the case of nitinol.
By contrast, the femtosecond laser produces a
burr-free cut that drastically reduces the number
of time-consuming postprocessing steps. The part
is machined and then undergoes an electrochemical process to round the edges. The integrity of the
part is improved, and yields can be closer to 95 percent. In addition, using a femtosecond laser can be
an attractive proposition for fabricators that may be
looking to bring the cutting process in-house, but
do not want to go through the arduous red tape of
also bringing in-house the necessary chemical post-
The finer elements of laser tube cutting
Technology advancements meet the needs
of next-generation designs
Ever hear of a femtosecond laser? It can mean a world
of difference for those manufacturers involved in laser
cutting stents and flexible tubes with intricate features.
Here water is used during the tube cutting to ensure that the laser does not harm the opposing wall’s interior