Whether it’s blastingthrough Inconel inminutes or taking

thousands of years to erode thenearly 300 miles of the GrandCanyon, the cutting power ofwater is easily recognizable.

Dr. Norman Franz, a forestryengineer, is widely regarded asthe father of waterjet technology.He was the first person to studythe use of high-pressure wateras a cutting tool. In the late1950s and early 1960s, Franzexperimented by droppingweights onto columns of waterand then forcing that waterthrough a tiny orifice, obtainingshort bursts of very high-pres-sured water. It was his goal tocreate a new tool for the lumberindustry, and, although he wasunsuccessful, he did prove thathighly pressurized water can beused as an effective cutting tool.

From these crude and experi-mental beginnings, waterjettechnology has changed tobecome one of the fastest growingsegments of the production cutting machine industry.

Today, thanks to the additionof an abrasive to the water, thenumber of applications for thistype of cutting continues to growfrom cutting hardened tool steeland alloys to glass and ceramics.

In terms of production, wherethis type of machine reallyshines, however, is in its flexibility.

“The push toward lean manu-facturing will really help themarket for waterjets because itis such a great tool. You canstart with a plate and make

many things out of the sameplate with no tool changes andhardly any fixturing,” said JohnOlsen, founder and chief technology officer of waterjetmanufacturer, OMAX.

How It WorksAfter pressurizing the water,

usually to between 40,000 and60,000 pounds per square inch(psi), and then forcing it througha small gem orifice (most commonly a sapphire, ruby ordiamond) speeds of 2,500 feetper second are reached. This isequivalent to roughly two-and-a-half times the speed of sound.

Following the passage throughthe orifice, an abrasive is fedinto the water and mixed in atube. A stream of abrasive-ladenwater moving at 1,000 feet persecond exits the tube and directedat the material to be cut. Sinceit’s the abrasive that is actuallycutting the material, it is one ofthe most important componentsin the entire system.

“Roughly, half of the cost ofrunning an abrasive waterjet isthe abrasive itself,” said Olsen.“And, because it is so much ofthe cost, people sometimes try toget away with buying the cheapestabrasive they can find.”

According to Olsen, this is nota good idea as poor quality abra-sives can often cause downtimethrough plugging the cutting nozzle.

The most commonly usedabrasive is garnet. Garnet ishard, tough and relatively inex-pensive, however, in some cases,

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Abrasive Waterjets:

aluminum oxide andother man-made mate-rials are used.Aluminum oxide isharder than the garnetsand, but it is alsomore expensive andquickly wears out themixing tube.

“Nearly all of thewaterjets use garnetbecause it is the mosteffective product,”

said Randy Rapple, general manager of Barton Mines, one ofthe largest garnet mining companies in the world. “The garnetquality also plays a huge role in how well the machine per-forms.”

When other abrasives are used, the life of the mixing tubesand orifices are severely reduced. When using garnet, it is notuncommon for a mixing tube to last 60 to 80 hours, however,when aluminum oxide is used, they need to be replaced every few hours.

However, all garnet is not created equal.“Saying garnet is a bit like saying automobile,” explained Rapple.“There is a spectrum of garnet products starting with andra-dite, which is a soft garnet, to almandite, which is a hard gar-net. Basically, all of the garnet sold into the waterjet market isalmandite.”

The best quality garnet is generally blasted and crushed

from hard rockdeposits, muchlike Barton’s openpit mine in NorthRiver, New York.The hard rockgarnet is moree x p e n s i v ebecause of thework associatedwith the miningprocess but alsoperforms betterdue to the sharperangles of the crystals.

Much likesandpaper grit,abrasives come indifferent meshsizes. Generallyspeaking, thecourser (andlower-numbered)mesh used, forexample a 40 or a50 mesh, the faster it cuts. The downside of using the coursematerial is that a rougher surface finish is produced.

Waterjet ConsumablesNeedless to say, the intense pressures and

abrasives cause certain parts of the machine towear and need replacement as a cost of runningthe machine.

For example, the three common types of orificegems - sapphire, ruby and diamond - each havetheir own attributes and lifetime. Sapphire andruby orifices generally create a good qualitystream, and can be used for roughly 25 to 75 hoursin an abrasive waterjet system.

A benefit of using a diamond, however, is thatthis gem has a considerably longer life (800 to2,000 hours) but is also 10 to 20 times moreexpensive. They are especially useful in applica-tions where 24 hour per day operation is required.

Usually, orifices will fail because they have beendamaged by the small particles hitting them.

“As soon as the orifice is damaged, stream qualityis spoiled. If you have a very poor orifice, it willquickly wear out the mixing tube, so the operatorhas to be aware of the stream quality or they willwear out mixing tubes very quickly,” said Olsen.

Other ConsumablesThe mixing tube adds the abrasive to the high-

pressure water, accelerating the abrasive particles.They, like the orifices, and other products thatcome in contact with the water, need to bereplaced.

While the operational costs involved in runninga waterjet machine can be high when compared to

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Hard rock garnet

other processes-roughly $25 per hour, plus the cost of the oper-ator-the flexibility of the machine, short set-up times and highproductivity can help justify the purchase.

Other consumables that need to be taken into considerationwhen purchasing a waterjet are water and power.

The water usage by the machine is actually quite low,depending on the application, but the same contaminants thatcause boiler scale (iron, silica, etc.) will cause problems forwaterjet nozzles as well. Also, fine particles in the water willcause problems for the orifice and also with some of the pumpcomponents. If this is the case, a reverse osmosis unit is neededin order to help clean the water before it enters the system.

Also, in hard water areas, which are areas where the groundwater contains calcium and magnesium, a water-softening unitcan be added to the system.

As the cost of electricity rises it is important to keep consumption down. One way to do this is by selecting the cor-rect type and size of pump.

All waterjet pumps work by pushing a plunger into a closedvolume and expelling the water. What makes the difference ishow you push the plunger. One type uses a crankshaft to pushit and another uses a hydraulic cylinder.

According to Olsen, the hydraulic pumping systems haveoverall power efficiencies in the 60 to 70 percent range, butthe crank drives run in the mid-90 percent area. This meansthat if you are running a 50 HP hydraulic drive unit, you’reusing more power than you really need. To drive the same jetmight take only a 30 HP crank drive.

According to Joe Cisar, senior applications trainer for waterjetmanufacturer Bystronic, another way to move the return strokeof the piston is by using air pressure.

“We have a new type of intensifier available that is calledactive pressure control, or the APC pump, and what it does iseliminate some of the hydraulics that are involved with creatingthe water stream,” he said. “Untilnow, we have used two hydraulicpumps - the larger one, which isused to compress the water withinthe cylinder and the smaller onewhich is used to return the pistonback and drawing water into thecylinder at the same time.”

Now, he said, the smaller one hasbeen replaced in order to helpreduce the amount of electricity thatis used. It has been replaced by anair pump and it is now air pressurethat returns the piston back anddraws in new water, rather than twosets of hydraulics.

“Every customer is looking to saveon the cost of operation whether it beelectricity, manpower or consum-ables,” added Cisar.

Benefits andApplications

According to Olsen, one of the realstrengths of a waterjet system is thevery short time required to programand set-up the machine to make a part.

A part that takes a full day for an experienced programmerand machinist to program and set-up on a more traditionalmachine may only take a few minutes to do on a waterjet. Forthis reason, they are ideal for short-run parts or prototyping.

Because the abrasive waterjet uses only water and abrasiveto do the actual cutting, the material is not heated during thecutting process. This makes the process ideal for materials thatare affected or deformed by heat, such as titanium. Anotheradvantage is that when compared to laser, there is a lower purchase cost involved, which can be helpful to a shop ownerwho is currently farming out work to a laser shop that can thenbe kept in-house.

While not as fast as laser or high definition plasma on gaugethickness mild or stainless steel, when you compare the cost ofa waterjet to the capital costs involved with the purchase of alaser, or the secondary work needed to clean up plasma work,

the final cost per part from a waterjet canmake it a good addition to a shop.

“There is a little bit of overlap as far ascompeting with a laser is concerned,” saidOlsen. “A laser cannot cut near the thick-ness that a waterjet can, nor can it cut stoneor glass. But, the waterjet cannot competewith the speed of a laser in thinner materials.”

According to David Dumas, sales manag-er of Jet Edge, the St. Michael, Minnesotawaterjet manufacturer, waterjets and laserscan complement each other on a shop floor.

“On two inch material, I can cut a lotfaster with a waterjet than a laser,” he joked.“A laser can’t cut through it. But as far asplasma or lasers are concerned, they aregoing to be much faster, but with plasma andlaser, you have to worry about secondaryoperations.”

Future of Waterjet“I think you’ll see pressures increasing,

bringing up the speed and also multiplehead cutting. New advances in the cuttingheads themselves will also be able to pro-duce tighter tolerances,” said Dumas.

“The word is getting out more and moreabout the benefits of waterjets. In the past it

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“Every customer is looking to save on thecost of operation whether it be electricity,manpower or consumables.”

High pressure water

Jewel (orifice)

Abrasive inlet

Mixing tube

was considered expensive and not reliable. It has come a longway since then,” he said.

According to Bystronic’s Cisar, waterjet systems will beginusing more automation as they start being used in producinghigher volumes.

“You are going to see a lot more people start looking at thehigh production end of waterjet cutting,” said Cisar. “Thesewill be people who want to constantly run the machine, notnecessarily the shops that want to make one or two parts or useit for prototyping.”

If you’re planning on running constant production on mate-rials that can’t be machined by conventional means, waterjet isa very good option, he said. Also, with new, high productionapplications will come the need for automation to becomeinvolved in the process.

“With our new shuttle table feature, we are pushing towardlights-out production,” he said. “What the waterjet does islower the water level, release a safety and the tables exchange,allowing a customer to continue with production without havingto stop work or any interaction from an operator.”

Waterjet is poised to be a great lights-out machine and it’sgreat for thick plate materials or materials that you can’t cutwith any other machining process and that’s one fact to rememberthat it can cut virtually any material.

You’re basically using the two forces of nature that erode -water and sand.

For more information, please visit www.barton.com,www.bystronicusa.com, www.jetedge.com and www.omax.com.■

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Garnet Mesh Sizes

50: Offers the most powerful cutting performance and speed. Used when cutting speed is more important than edge quality. Materials: thick stainless steel, titanium and stone.

65: Combines the cutting power of 50 with the edge quality of 80. Materials: thick materials where surface finish is important.

80: Offers fast cutting speed and good edge quality. Materials: wide variety, including all metals, composites, ceramics and stone.

85: Offers the cutting power of 80 with superior edge quality. Materials: wide variety, including all metals, composites, ceramics, and stone.

120: Offers superior edge quality and cutting speed. Materials: steel, aluminum, glass, ceramics, laminates, composites and other brittle materials.

150 and 220: Specialty grades for applications with very demanding, fineedge requirements. Materials: composites, printed circuit boards and fiber optic cables.