Parts cut using abrasive waterjets. (Images courtesy of Jet Edge, Omax and
Flow International.)You don’t get much closer to the spirit of engineering than
in the beginnings of waterjet cutting.
“I got started years ago, in about ’71,” said Dr. John Olsen, one of the
originators of waterjet technology and currently VP of operations at Omax
Abrasive Waterjets. “I had been reading about some experiments done on rock
cutting in England and a friend of mine and I thought it would be fun to try and
build a pump and cut something. That was a kind of back-alley operation; it was
in my garage and his garage.”
Dr. John Olsen holding a tilting head waterjet with two linear actuators.
(Image courtesy of Omax.)It might sound like many of the stories you hear about
start-ups in Silicon Valley today, but the connections between waterjet and
computing technologies run deeper than that, as Dr. Olsen explained:
“Oddly enough, one of the biggest changes that made abrasivejets practical
was the advent of the PC. A jet is not a very rigid tool—it bends all over the
place and makes taper and what-have-you. To make precision parts, you need quite
a bit of computing power to predict what the shape of the jet will be so that
you can compensate for it. At the time, we were told ‘Nobody will ever accept a
PC on the factory floor. Doesn’t that sound funny today?”
Pure vs. Abrasive Waterjet
Abrasive waterjet nozzle. (Image courtesy of Omax.)In the broadest sense,
the term ‘waterjet’ encompasses any cutting tool that utilizes a high-pressure
stream of water. More specifically, waterjets can be divided into pure and
The term ‘pure waterjet’ refers to cutting tools that use only water, while
the term ‘abrasive waterjet’ or sometimes just ‘abrasivejet’ refers to—as you
might have guessed—waterjets that use an abrasive to accelerate the cutting
Pure waterjet is used for cutting softer materials, including gasket, foam,
food, paper, plastic and carpet.
Abrasive waterjet is used to cut harder materials, such as metal, ceramic,
stone, wood and glass.
Waterjet abrasives are typically made of garnet, with grit size ranging
from 50 to 220 mesh, though 80 is the most common. Many waterjet machines are
capable of switching from pure waterjet cutting to abrasive waterjet cutting,
making them uniquely versatile.
Versatility is one of the primary strengths of waterjet technology. To
illustrate the sheer number of materials that can be cut using a waterjet, Chip
Burnham, vice president of global marketing for Flow International Corporation,
provided a list of materials in order of cutting speed, from slowest to fastest,
for any given constant material thickness:
Sample list of materials that can be cut on an abrasive waterjet in order
of cutting speed from slowest to fastest.This list is by no means exhaustive and
it’s actually easier to list the things that waterjet can’t cut.
“There’s only a few things that I haven’t been able to cut in my career,”
“One of them is tempered glass—although some people still do it, the
tempered glass has to be resealed after because it has stresses in it and when
you cut it with waterjet you relieve the stresses. I cut beautiful things out of
tempered glass and astonished glassmakers in the early years of waterjet just to
come back into the lab the next day and find it in a million pieces because it
Scott Wirtanen, regional sales manager at Jet Edge, also emphasized the
versatility of waterjet cutting: “Waterjet’s going to perform almost identically
in almost any material. So the versatility of waterjet, both in materials and in
thicknesses is unparalleled.”
If you’ve spent even a little time with waterjet engineers, you’re probably
familiar with a longstanding topic of debate: how much of a difference does
One way to understand the sheer amount of pressure involved in waterjet
cutting is to compare it with other water sources in terms of maximum pounds per
square inch (psi).
Logarithmic scale comparing four sources of water in terms of upper
As this graph makes clear, pressure can make an enormous difference—like
the one between washing your hands and cutting them off. But the pressure
variation within waterjet is much narrower, typically 60,000 - 90,000 psi.
Some engineers argue that higher pressure is the key to faster cutting,
while others contend that what really matters is motor efficiency.
In order to give both sides a fair shake, let’s take a moment to consider
their respective arguments.
90,000psi vs 60,000psi
The 90k advocates point out that increasing the waterjet pump pressure from
60,000 psi to 90,000 psi increases the velocity of the stream, which they argue
increases cutting speed by 50 percent or more, depending on the application.
A Flow Mach 4c Dynamic XD waterjet cutting carbon fiber. (Image courtesy of
Flow International.)They also claim that cutting at 90,000 psi reduces abrasive
consumption, since each garnet particle is imparted with more energy. Finally,
the higher working pressure when piercing and cutting is supposed to reduce
delamination for composite materials.
“Cut speed is tied directly to nozzle horsepower,” said Burnham. “So
horsepower consumed is a function of the amount of water that’s exiting the
orifice and the pressure. A small orifice with low pressure consumes very little
power and cuts slowly. In contrast, a larger orifice with high pressure will
consume a lot of power and cut more quickly. It’s the amount of water and the
pressure that is demanding the horsepower.”
Wirtanen agrees, stating that if you were to use the same orifice-nozzle
combination, the same amount of abrasive and the same volume of water, 90,000
psi will still outperform 60,000 psi every time.
“However,” he added, “the area can be a bit clouded when you start to look
at dual cutting heads using one pump. For example, a 60,000 psi intensifier pump
at 100 horsepower will produce two gallons per minute. A hundred horsepower pump
at 90,000 psi will put out approximately 1.4 or 1.5 gallons per minute. So the
ability to drive dual cutting heads at that point is limited on the 90,000 psi
pump because of the GPM that it’s capable of.”
A dual-head Mach 4c waterjet. (Image courtesy of Flow International.)
Wirtanen continued, “At 1.4 or 1.5 GPM with a 90,000 psi, 100 horsepower
pump, you’re able to run at max pressure through 0.011” orifices. A 100
horsepower, 60,000 psi pump can run through 0.015” orifices. So because of that
difference driven by the GPM capability on either pump, you’re almost cutting at
the same cutting speed with dual heads.”
In reply to these claims, 60k supporters point out that if you increase
pressure then you need to reduce the size of the nozzle. This is based on the
fact that power is proportional to pressure times volume flowrate, as
represented in the formula:
Power = kPV
Advocates of 90k might reply that the higher pressure, smaller volume
nozzle will cut faster because it has higher power density (i.e., the same
amount of power in a smaller area), but 60k supporters deny that this is true
outside of pure waterjet applications.
“One of the big issues is that if you want to pump at 90,000, then you’re
stuck with an intensifier and an intensifier pumping system is so inefficient
that you actually get more cutting power at lower pressure with a direct-drive
pump,” said Olsen. “So the efficiency trumps pressure.”
This brings up an important distinction in waterjet and another
controversial topic: intensifiers and direct drive pumps.
Waterjet Pumps: Intensifier vs Direct Drive
Schematic of a hydraulic intensifier pump. (Image courtesy of Jet
Edge.)There are two basic types of pumps in waterjet: direct drive and
intensifier. Direct drive pumps use a crankshaft to move the plungers that
pressurize the water, whereas intensifiers use hydraulic rams.
Each type has advantages and disadvantages, as Wirtanen explained:
“Direct drive pumps are inherently a simpler design, but do require a
dramatically higher amount of maintenance than an intensifier pump. Because
they’re a simpler designer, they’re less expensive for an initial investment,
but in the long run, the intensifier pumps have a dramatically lower cost of
Schematic of a direct drive pump. (Image courtesy of Jet Edge.)Hence, if
the initial investment is your primary concern, then a direct drive pump is the
way to go. On the other hand, if you’re looking for the lowest maintenance cost,
an intensifier pump is the better option. This illustrates one of the basic
tenets of manufacturing: it all comes down to your particular application.
As with any fabrication technology, there are multiple ways to calculate
waterjet costs. However, some provide a more accurate estimate than others. For
example, trying to calculate costs in terms of dollars per hour of machine time
is problematic because waterjets can be configured with single or multiple
cutting heads, which affects cutting times.
Thick foam parts cut by a Flow Mach 4c Dynamic XD waterjet. (Image courtesy
of Flow International.)The typical price range for a waterjet with a single
cutting head is approximately USD$100-135 per hour, though high-end parts can
run up to $2,000 per hour depending on material type and thickness as well as
part geometry. These same three factors are what makes it difficult to calculate
waterjet costs in terms of dollars per square inch of material cut, since they
all contribute to longer cutting times.
The best approach to calculating waterjet costs is in terms of dollars per
part. However, there is a large list of factors that go into such calculations,
The time it takes to program the toolpath
Risk of breakage with fragile material
How many times the material needs to be pierced
Cost of consumables
Setup, unloading and maintenance time
Common Misconceptions about Waterjet Cutting
Cutting head on a MAXIEM 1515 JetMachining Center. (Image courtesy of
Omax.)“When they began, they were kind of the tools of last resort,” explained
Dr. Olsen. “The jet was not a very rigid, precise cutting tool and so early
abrasive jets—say, in the ‘80s—were used if you had absolutely no other possible
way to cut the material. Then you would pick an abrasive jet and expect to have
a very imprecise cut, almost like oxy acetylene burning. Because waterjets
started with that application, it’s been a long struggle to get them accepted as
a precise machining technique.”
Another common misconception about waterjets concerns their ability to cut
thicker materials, as Burnham explained: “People say that water and abrasive
can’t cut thick [sections], but we can cut through over a foot thick in pretty
much any common material. We’ll have to cut slower, but it does have the ability
to cut thick."
A thick steel gear cut with waterjet. (Image courtesy of JetEdge.)“I have
people who are saving weeks of cutting by roughing out material that is 24”
thick,” Burnham added. “They rough it out and then put it on a mill and by
roughing it out save weeks of milling time, but that’s not common—most cutting
these days is three inches or less.”
Of course, the fact that you can save time by roughing with waterjet
doesn’t mean that it’s a particularly fast cutting method compared to plasma or
“A lot of customers will expect to cut at the same speeds as a laser or
plasma,” Wirtanen observed. “Waterjet is definitely slower, so the importance of
dual cutting heads or three of four cutting heads certainly can’t be
This brings us to the inevitable comparisons between waterjet and other
cutting technologies, including laser, flame and plasma cutting. Although each
cutting method has its own advantages and disadvantages, waterjet has often been
overlooked despite the benefits it offers.
“That’s beginning to change now,” said Dr. Olsen, “but for at least ten
years I would say that was the case. But it’s beginning to change because it’s
become popular and it’s now used as a first operation for almost anything a
person would want to make. A lot of shops are using waterjet that way.”
So what are the advantages of waterjet?
Advantages of Waterjet Cutting
Waterjet has two main advantages compared to other cutting techniques:
versatility and simplicity.
Its versatility is illustrated by the sheer variety of materials and
thicknesses that can be cut on a waterjet, but its simplicity is best
illustrated by comparing waterjet to laser, plasma and flame cutting.
Waterjet vs. Laser
Laser cutting.In laser cutting, a focused beam of light is used to melt,
burn or vaporize the material being cut. The laser can be static, with the
material moving underneath it, or it can move across the material which remains
fixed in place. In the latter case, additional optics are required to compensate
for changes in distance from the emitting end of the laser.
Although laser cutting is often seen as complimentary to waterjet, with
many shops using both technologies, the latter does have some distinct
advantages over the former.
“In comparison to a laser, for example, when you look at titanium or
stainless steel or aluminium, there’s limited capacity with regard to thickness.
I think the max thickness in general is around an inch and a quarter to an inch
and a half,” said Wirtanen.
“We’ve cut through eight- or nine-inch-thick material. When you look at a
laser’s capabilities, it’s commonly understood that there’s difficulty in
processing reflective materials, like aluminum or any of the yellow metals like
bronze or copper,” he added.
In other words, materials and material thicknesses that are difficult or
impossible to cut with a laser tend to pose little difficulty for a waterjet.
This ability to cut thick materials is one reason waterjet is a popular choice
for roughing out parts—surface finish is another.
“The beautiful thing about finishing a rough cut from a waterjet on a mill
is that it’s a virgin surface that has gone through an erosion process,” said
Burnham. “If you try to rough cut with plasma or a laser and then finish it on a
mill, you’re removing work-hardened and heat-hardened material.”
This brings up one of the biggest advantages of waterjet cutting, which is
the absence of heat-affected zones (HAZ). This a problem for laser cutting and
another competing fabrication technology: plasma cutting.
Waterjet vs. Plasma
Plasma cutting.Plasma cutting operates on electrically conductive materials
using an accelerated stream of gas which is superheated into plasma via an arc
of electricity. The plasma melts the material while moving fast enough to blow
molten metal away from the cutting area.
Although it’s typically faster than waterjet, plasma cutting suffers when
it comes to surface finish.
“Plasma can outperform waterjet with regard to speed, but the cut quality
is far inferior,” said Wirtanen. “With regard to edge quality, tolerance
capability, and the secondary operations that are required with plasma, you
don’t see those with waterjet.”
The HAZ makes secondary operations for plasma (and laser) cutting even more
problematic, since HAZs can harden surfaces and make them more brittle. This in
turn makes it more difficult to complete secondary operations, like tapping or
Another advantage waterjet has over plasma in particular is the ability to
cut materials that don’t easily melt, like granite, or materials that are
destroyed by melting, like laminates.
Waterjet vs. Flame Cutting
Flame cutting.Flame cutting, which is only used for iron and steel,
involves heating metals to high temperatures and then introducing oxygen to melt
the metal for the cut. The heated metal reacts to the oxygen and forms iron
oxide, which has a lower melting point than the metal itself.
Once again, the primary advantage waterjet has over this competing cutting
technology is its ability to cut more than just iron and steel. Unlike flame
cutting, which creates heat-affected zones, waterjet cutting does not
appreciably heat the material being cut. Although it may get as hot as 120° F
(49° C) during piercing, the material is only heated a few degrees during
Waterjet cutting is also more precise than flame cutting and the former
leaves an almost sandblasted finish, which is significantly smoother than the
rough edges produced with flame cutting. The smaller kerf produced using
waterjet is another advantage, particularly when cutting expensive
The Future of Waterjet
Despite its versatility and simplicity, waterjet remains a relatively niche
cutting technology. There are numerous reasons for this state of affairs, but
Burnham emphasized one in particular:
“What’s the most common hard material cut? It’s mild steel, which
everything can cut—plasma can cut it, laser can cut it, punches, mills, routers,
saws; everyone can cut mild steel. Moving up to plate, still a lot of processes
can cut mild steel in plate. Basically, as you get away from the super-common
materials into the more exotic materials, and you get a thicker, like up to a
foot thick, then you’re getting into the realm where waterjet shines.”
Metal gears cut on a waterjet. (Image courtesy of Flow International.)This
suggests that as manufacturers move into more exotic materials, the demand for
waterjet will increase. So if you’re looking to get into waterjet cutting, where
should you begin?
“The biggest thing is to have test cuts made to be sure it does what you
think it’s going to do,” Dr. Olsen advised. “You want to know how precise the
part came out. Is the surface finish okay for my application? How long did it
“Those things are best known by actually making a part that’s indicative of
the kind of parts you intend to make. There are lots of things to watch out for.
For example, if you’re making things out of carbon fiber and you want to cut
that up, then you have to watch and learn about delamination upon piercing and
have a way to minimize that,” he concluded.