Photo courtesy Finepart Sweden AB
Abrasive Waterjet Technology
Scaling Down
Waterjets to
the Micro Level
The Finecut abrasive waterjet cuts titanium, generating sparks as
new surfaces of the erosion fragment under exothermal reaction
with air. The system uses fine-grained precision powder abrasives
to produce very fine surfaces in the range of 1 µm in Ra value.
New technical advances are moving
abrasive waterjet technology squarely
into the micromachining realm
Patrick Waurzyniak
Senior Editor
S
hrinking an abrasive waterjet machine down
to work at micro sizes is no small task.
Adapting abrasive waterjets for micromachining requires greatly reducing the size of the
waterjet nozzles and mixing tubes that carry
smaller garnet abrasives through the water-
jet’s high-pressure cutting tool delivery system.
Abrasive waterjet machining excels as a versatile
alternative cutting process capable of cutting virtually any
material, from exotic alloys and titanium to stainless, ceramics, glass, rubber and plastics. A cool process, abrasive
waterjet machining has no heat-affected zone (HAZ), unlike laser or wire EDM processes, and it offers a substantial
speed advantage over EDM.
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Abrasive Waterjet Technology
In the last few years, some key advancements in downsiz-
Micro Waterjets Gaining Wider Acceptance
ing abrasive waterjet technology have been developed by Pe-
Among the barriers to wider use of micro waterjets is
ter Liu, senior scientist, OMAX Corp. (Kent, WA), whose work
changing the mindset of some machine shop owners. “The
under a National Science Foundation (NSF) Small Business
main obstacle may be in the mindset of precision workshop
Innovation Research (SBIR) grant culminated in August with
owners that have recently tried state-of-the-art standard water-
OMAX’s release of its new MicroMax JetMachining Center.
jet systems,” said Christian Öjmertz, CEO of Finepart Sweden,
This machine is primarily aimed at cutting very thin metals
developer of the Finecut micro waterjet machining systems
used in medical, aerospace and other industries. It features a
introduced in 2009. “The fact that the level of tolerance of the
high-precision 0.1-µm linear optical encoder system, a highly
waterjet process now can be 10 times higher than what was
rigid structure, and patent-pending processes for feeding fine
available only a few years ago can be difficult to digest.
abrasive at a constant flow rate. OMAX’s 7/15 Mini MaxJet5i
“To be able to obtain fine tolerances with micro abrasive
nozzles reach position repeatability of better than ±0.0001"
waterjets you need to keep process parameters very stable,”
(±2.5 µm) and positioning accuracy of ±0.0006" (±15 µm).
Öjmertz said. “Water pressure variations should be kept at a
While OMAX isn’t the first company with micro abrasive wa-
minimum and abrasives are precision-fed [only 20–30 g/min
terjet systems, it may be refining the technology to another level.
is used for a 200–300-µm nozzle size]. Abrasive media must
Other abrasive waterjet micromachining systems on the market
be of very fine quality, and we test abrasive for approval to use
in recent years include systems from Finepart Sweden AB (Bol-
in the Finecut process. The abrasive media should be free
lebygd, Sweden) and Micro Waterjet LLC (Huntersville, NC).
from fine dust as it binds moisture that can obstruct the flow.”
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Abrasive Waterjet Technology
Fittings and nozzle shape are important to achieve fine
ances within ±0.01 mm,” Öjmertz said. Micro abrasive
tolerances, Öjmertz said. “An ovality in the nozzle bore of
waterjets require a special machine design to obtain the fine
0.01 mm will cause a reduced capacity to maintain toler-
tolerances, he added, noting that Finecut machines are built
with linear drive motors to prevent backlash problems and
provide excellent dynamics.
With the Finecut micro systems, tolerances to ±0.01 mm
can obtained, depending on material and part geometry,
Öjmertz said. “The micro AWJ [abrasive waterjet] utilizes a
Photo courtesy OMAX Corp.
fine-grained precision powder abrasive and produces very fine
surfaces in the range of 1-µm in Ra value. The surface roughness depends on the type of material being cut and in general
harder materials will exhibit finer surfaces.”
Using AWJ abrasive waterjet machining for micro parts
offers some advantages over other alternative machining
With the OMAX MicroMax abrasive waterjet, users can cut
processes, noted Steve Parette, managing director, Micro Wa-
parts or part features smaller than 400 microns across a
terjet LLC. “When compared to laser and wire EDM, you have
wide range of materials including exotic metals, titanium,
no heat-affected zones [HAZ],” Parette said, “and there is a
advanced composites, polymer thermoplastics and glass.
wider range of material compatibility with abrasive waterjet.
• Precise metal and plastic marking capabilities
• Generous 32" x 20" work area
• Advanced job control for increased throughput
• Power configurations up to 50 watts
• Joystick control for easy operation
• High-quality, USA-Made Equipment
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Micromachining requires special tooling depending on the
technical hurdles for abrasive waterjet micromachining applica-
application. Abrasive waterjet uses no special tooling.
tions. “We decided to get the nozzle size as small as possible,
“We concentrate on thin materials, usually 2 mm and
thinner,” he said. “The finest finish achieved is N6, or 32 mi-
especially the mixing tube, which governs the kerf width of the
part,” Liu said. “And it turns out that even though you want to go
croinches; currently parts are being cut
in production with tolerances ±0.0005"
[±0.010 mm].”
Micro or Not?
With its NanoJet abrasive waterjet,
Flow International offers a specialized
small-footprint system for semiconductor singulation. It features a Paser
ECL abrasive cutting head, a patented
vacuum assist feature, integrated vision
positioning system, and an X-Y-Z cutting
envelope of 32 × 13 × 3.5" (820 × 480
× 90 mm). Linear servomotors help
enable path accuracy to ±0.001" (0.025
mm) and repeatability to ±0.001".
“The first need for thin-kerf cutting
with abrasive waterjet was about 10 years
ago, in the semiconductor industry,” noted Mohamed Hashish, Flow International
senior vice president, Technology. “At
the time, the state of the art of waterjet
diameter was in the 20 thousandths of
an inch and above. Features on microSD
cards needed to be smaller than that.
“Different people define micromachining differently, and in the waterjet
industry it’s addressed very loosely, so
in a way, coming from a micro level is
probably inaccurate,” said Hashish. “In
my opinion, we’re not talking about micro jets. We’re talking about jets that are
in a few microns, and we are in a few
tens of microns, so we are in an order of
magnitude higher than microns.”
Moving Microjets Forward
During the past three years, Liu’s
research at OMAX under the NSF’s
$550,000 SBIR II grant has concentrated
on reducing the nozzle size among other
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Abrasive Waterjet Technology
down as small as possible, there are limitations, for example, one
of which is the capability of making a mixing tube that small.”
Working with development partner Kennametal Corp.
(Latrobe, PA), supplier of abrasive waterjet nozzles made of
composite carbide, Liu was able to significantly shrink the
size of the nozzles. Kennametal, which exclusively licenses
the ROCTEC (Rapid Omnidirectional Compaction) process for
developing a tungsten carbide-based material used in mixing tubes, is a major supplier of abrasive waterjet nozzles to
waterjet machine tool builders. “I’ve been working with them
all along,” Liu said. “The best they can do is something around
6–8 thousandths of an inch [0.15–0.20 mm] in the ID of the
mixing tube, in order to get good quality, or circular, holes
through the length of it, and the material’s one of their best that
allows minimizing the wear for abrasive waterjet applications.”
With Kennametal, Liu worked on downsizing the nozzles
and mixing tubes, eventually developing a 5/10 nozzle version—with a 0.005" (0.13-mm) orifice and 0.010" (0.25-mm)
mixing tube—that is currently being beta tested. “We wanted to
see how small we can go,” he said. “Now the obstacle is, from
a pure fluid mechanics point of view, how small of a mixing
tube can you squeeze the waterjet through? When you have a
large mixing tube, with a large diameter, the flow or the fluid
mechanics is the so-called gravity flow. But when you get down
to a very small one, then the capillary effect on it becomes
important—you actually increase the resistance through the
mixing tube. The surface tension becomes important, instead of
gravity, so the process is dominated by the capillary effect.”
Liu offered a simple example of the process: “If you have
a glass tube with a small diameter and you put in water, you
can see the column of water rise through the tube—that is the
capillary effect. When you look at the resistance of the flow
through the small tube, it is inversely proportional to the fourth
power of the diameter. That means the smaller the tube you
go through is, the higher the resistance—sooner or later, you
just don’t have anything squeezing it through, and it’s probably
60,000 psi.” Increasing the pressure of the abrasive waterjet
micromachining applications becomes difficult given those
circumstances. “It’s the so-called entrainment pressure of
abrasive waterjet,” Liu added. “We are working on ways to
overcome that, but it will take additional research.”
Refining Abrasive Delivery
The smallest production nozzle currently available from
OMAX is the 7/15 Mini MaxJet5i on its new MicroMax machine,
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November 2013
which features a 0.007" (0.18-mm) orifice and a 0.015" (0.38-
tion.” This waviness, similar to chatter on a CNC-machined part,
mm) mixing tube combination for quickly and accurately cut-
is reduced with the MicroMax’s rigid, vibration-isolating design.
ting delicate, complex patterns. The system’s jet stream uses an
extremely fine abrasive with the nozzle, producing a kerf width
Reducing the mixing tube size also requires substantially
reducing the size of the abrasives, Liu noted. As the garnet
as small as 0.015", and the machine also
features advanced pressure controls for
piercing delicate materials.
OMAX’s 5/10 nozzle has been in
beta-testing for two years now, and is
not yet commercially available. “When
you are trying to cut very thin material,
our current cutting model is not quite
accurate enough,” Liu said. “That’s the
reason why we don’t want to release it as
a product yet. At this point, we are working on the program so that we can accurately describe it so that the customer will
not have to do a lot of tweaking.”
Among the main aims of the SBIR
Phase II project for OMAX was development of micro abrasive-waterjet technology for automated machining features
between 50 to 100 µm, according to
the SBIR grant description, which cites
the biggest challenge being development of nozzles with beam diameters
less than 100 µm. Several issues must
be resolved due to the complexity of the
supersonic, three-phase, and microfluidic flow through micro abrasive-waterjet
nozzles in which, as Liu described
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above, capillary dominates gravity.
For medical parts, the new OMAX
micro waterjet has shown it cuts titanium
faster than stainless, Liu said, with titanium cutting as much as 34% faster for
skull meshes, spinal implants and other
components. Another key to achieving
high precision with the 5/10 beta nozzle
is the new machine’s stability, Liu added.
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“We found that one critical area is that
you must keep your nozzle stable. In other
words, you cannot have any vibration.
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When you are cutting a very small part,
any vibration will cause some wavy forma-
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Abrasive Waterjet Technology
abrasives get smaller, they tend to clump together with poor
OMAX’s cutting model, surface roughness should be less than 5
flow. “You want to have the particle size about one third of the
µm. “It depends on what size of garnet you use,” Liu said. “The
ID of the mixing tube,” Liu stated. “If you have only two times
finer the garnet you use, the better the surface finish.” ME
smaller, two of the particles can be bridged inside the mixing
tube and cause clogging, but if you have three times smaller,
that would be very difficult to have three particles lined up and
clog your nozzle. It’s both a theoretical and practical limitation.
“The smaller the abrasive, the better the surface finish
you’ll be able to get,” Liu said. “Under certain circumstances,
you want to go even smaller, but now the problem comes in,
when you have large particles like the one we’ve been using
with our production system, those can flow very well under
gravity feed. When you go down to the powder size, they tend
to clump together. I have developed a couple novel processes
[patents-pending] that allow us to avoid that type of problem.”
Flow rate is key to the process, with a constant flow rate
enabling better cuts, Liu said. With the MicroMax’s 5/10 nozzle
and using a fine 320 mesh garnet at the top quality setting in
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Want More Information?
Finepart Sweden AB
Ph: +46 70 6763355
Web site: www.finecut.se
Flow International Corp.
Ph: 253-850-3500
Web site: www.flowcorp.com
Micro Waterjet LLC
Ph: 704-948-1223
Web site: www.microwaterjet.com
OMAX Corp.
Ph: 253-872-2300
Web site: www.omax.com