Abrasive Waterjet Technology Scaling Down Waterjets to the ... · Scaling Down Waterjets to the Micro Level ... Other abrasive waterjet micromachining systems on the market ... •

November 2013 | ManufacturingEngineeringMedia.com 59

Shrinking an abrasive waterjet machine down

to work at micro sizes is no small task.

Adapting abrasive waterjets for micromachin-

ing 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, ce-

ramics, glass, rubber and plastics. A cool process, abrasive

waterjet machining has no heat-affected zone (HAZ), un-

like laser or wire EDM processes, and it offers a substantial

speed advantage over EDM.

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.

Scaling Down Waterjets to the Micro Level

New technical advances are moving abrasive waterjet technology squarely into the micromachining realm

Patrick WaurzyniakSenior Editor

Abrasive Waterjet Technology

Photo courtesy Finepart Sweden AB

In the last few years, some key advancements in downsiz-

ing abrasive waterjet technology have been developed by Pe-

ter Liu, senior scientist, OMAX Corp. (Kent, WA), whose work

under a National Science Foundation (NSF) Small Business

Innovation Research (SBIR) grant culminated in August with

OMAX’s release of its new MicroMax JetMachining Center.

This machine is primarily aimed at cutting very thin metals

used in medical, aerospace and other industries. It features a

high-precision 0.1-µm linear optical encoder system, a highly

rigid structure, and patent-pending processes for feeding fine

abrasive at a constant flow rate. OMAX’s 7/15 Mini MaxJet5i

nozzles reach position repeatability of better than ±0.0001"

(±2.5 µm) and positioning accuracy of ±0.0006" (±15 µm).

While OMAX isn’t the first company with micro abrasive wa-

terjet systems, it may be refining the technology to another level.

Other abrasive waterjet micromachining systems on the market

in recent years include systems from Finepart Sweden AB (Bol-

lebygd, Sweden) and Micro Waterjet LLC (Huntersville, NC).

Micro Waterjets Gaining Wider Acceptance

Among the barriers to wider use of micro waterjets is

changing the mindset of some machine shop owners. “The

main obstacle may be in the mindset of precision workshop

owners that have recently tried state-of-the-art standard water-

jet systems,” said Christian Öjmertz, CEO of Finepart Sweden,

developer of the Finecut micro waterjet machining systems

introduced in 2009. “The fact that the level of tolerance of the

waterjet process now can be 10 times higher than what was

available only a few years ago can be difficult to digest.

“To be able to obtain fine tolerances with micro abrasive

waterjets you need to keep process parameters very stable,”

Öjmertz said. “Water pressure variations should be kept at a

minimum and abrasives are precision-fed [only 20–30 g/min

is used for a 200–300-µm nozzle size]. Abrasive media must

be of very fine quality, and we test abrasive for approval to use

in the Finecut process. The abrasive media should be free

from fine dust as it binds moisture that can obstruct the flow.”

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Fittings and nozzle shape are important to achieve fine

tolerances, Öjmertz said. “An ovality in the nozzle bore of

0.01 mm will cause a reduced capacity to maintain toler-

ances within ±0.01 mm,” Öjmertz said. Micro abrasive

waterjets require a special machine design to obtain the fine

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

fine-grained precision powder abrasive and produces very fine

surfaces in the range of 1-µm in Ra value. The surface rough-

ness 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

processes, noted Steve Parette, managing director, Micro Wa-

terjet LLC. “When compared to laser and wire EDM, you have

no heat-affected zones [HAZ],” Parette said, “and there is a

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 confi gurations up to 50 watts

• Joystick control for easy operation

• High-quality, USA-Made Equipment

e p i l o g l a s e r . c o m / m e • 8 8 8 - 4 3 7 - 4 5 6 4



With the OMAX MicroMax abrasive waterjet, users can cut

parts or part features smaller than 400 microns across a

wide range of materials including exotic metals, titanium,

advanced composites, polymer thermoplastics and glass.

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See us at FABTECH Booth #N1282

Micromachining requires special tooling depending on the

application. Abrasive waterjet uses no special tooling.

“We concentrate on thin materials, usually 2 mm and

thinner,” he said. “The finest finish achieved is N6, or 32 mi-

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 semicon-

ductor 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,” not-

ed 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 microma-

chining 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 mi-

cro 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

technical hurdles for abrasive waterjet micromachining applica-

tions. “We decided to get the nozzle size as small as possible,

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


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 mix-

ing 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 ver-

sion—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,



See us at FABTECH Booth #S901

which features a 0.007" (0.18-mm) orifice and a 0.015" (0.38-

mm) mixing tube combination for quickly and accurately cut-

ting delicate, complex patterns. The system’s jet stream uses an

extremely fine abrasive with the nozzle, producing a kerf width

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 work-

ing on the program so that we can accu-

rately 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 develop-

ment of micro abrasive-waterjet technol-

ogy for automated machining features

between 50 to 100 µm, according to

the SBIR grant description, which cites

the biggest challenge being develop-

ment of nozzles with beam diameters

less than 100 µm. Several issues must

be resolved due to the complexity of the

supersonic, three-phase, and microflu-

idic flow through micro abrasive-waterjet

nozzles in which, as Liu described

above, capillary dominates gravity.

For medical parts, the new OMAX

micro waterjet has shown it cuts titanium

faster than stainless, Liu said, with tita-

nium 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.

“We found that one critical area is that

you must keep your nozzle stable. In other

words, you cannot have any vibration.

When you are cutting a very small part,

any vibration will cause some wavy forma-

tion.” This waviness, similar to chatter on a CNC-machined part,

is reduced with the MicroMax’s rigid, vibration-isolating design.

Reducing the mixing tube size also requires substantially

reducing the size of the abrasives, Liu noted. As the garnet

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abrasives get smaller, they tend to clump together with poor

flow. “You want to have the particle size about one third of the

ID of the mixing tube,” Liu stated. “If you have only two times

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

OMAX’s cutting model, surface roughness should be less than 5

µm. “It depends on what size of garnet you use,” Liu said. “The

finer the garnet you use, the better the surface finish.” ME



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 LLCPh: 704-948-1223

Web site: www.microwaterjet.com

OMAX Corp.Ph: 253-872-2300

Web site: www.omax.com

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Abrasive Waterjet Technology Scaling Down Waterjets to the ... · Scaling Down Waterjets to the Micro Level ... Other abrasive waterjet micromachining systems on the market ... •