Flow Waterjet Cutting Frequently Asked Questions

flow waterjet cutting
Waterjet Cutting Questions
Still have questions about a Flow waterjet capabilities? Are you interested in waterjet cutting but are unsure of how a waterjet will benefit your business?

Why should I use waterjet cutting over lasers?
Laser cutting is a very productive process and certainly has its place. However, waterjets do have several advantages over lasers:

  • No thickness limitations.
  • No problems with reflective materials such as brass and aluminum.
  • No heat input, so there is no burning or heat-affected zone (HAZ).
  • Waterjets can cut materials which are heat sensitive such as plastics, rubber or composites, and even such materials as glass, stone and very hard ceramics.
  • When you change materials, the only thing you change is the cut speed. There are no gases, optics, or anything else to change.
  • Multiple heads are easily added for increased production.
  • Maintenance on laser equipment is more specialized and more difficult to perform.
  • Stand off distance between nozzle and material is not nearly as critical.
  • Waterjets typically require less of a capital investment than lasers.

….. over wire EDM?
EDM is extremely accurate, but very slow. It also requires an electronically conducive material and produces a heat-affected zone. For many applications, Dynamic Waterjet technology can produce parts approximating the accuracy of EDM for a fraction of the cost and time.

….. over milling?
If you are through-cutting the periphery and holes, rather than blind holes, pockets, and threads, the abrasive waterjet is typically much faster, easier to program and cheaper than milling. This is largely due to the fact that we cut a part with one pass, and we do not have to reduce all the metal to chip form. In addition, the scrap is usually more valuable in solid form than chip form.

….. over plasma or oxy fuel?
Obviously, plasma is a hot process. It adds a great deal of heat to the product, leaving a heat-affected zone. The surface finish of the abrasive waterjet is generally better. It leaves no dross on the backside of the part, reducing secondary operation. Abrasive waterjets have no thickness limitation , and can be much more closely nested.

What tolerances can we expect from waterjet cutting? Over 80% of the world’s abasivejet users cut parts to ±0.003-in. or looser accuracy. However, there is a percentage of users who cut parts to tolerances as tight as ±0.001 and even ±0.0005in. The accuracy you will get depends on whether or not you have Dynamic Waterjet technology, the accuracy of the machine, part size and part thickness.

Should I cut underwater?
Cutting underwater will do a couple of good things for you. First, it will reduce the noise of the cutting process to under 75 dB. Second, it will eliminate the frosting of the top surface of the material within 1/16″ of the jet (it can also be helpful if one is able to pass low-pressure water over the mixing tube).

The down side of cutting underwater is that you can’t see the cutting process. You also have to work underwater for material handling, unless you have water level control on your catcher.

How thick can it cut?
Up to 8-in. thick steel and titanium are cut on a production basis. There have been cases where 12″ and even 15in thick material has been cut. The vast majority of users, however, cut between 1/4″ to 2″ thick materials.

20″ Stainless Steel for Underwater Ship Nose, Photo courtesy of Mader Mannheim Germany

What kind of abrasive are you using?
Garnet is by far the most commonly used abrasive material. Users have found garnet to be the best for them in terms of cost, cut speed, mixing tube life, and health hazards. Other abrasives include olivine sand, aluminum oxide, and some man-made materials.

At what pressure do you cut? 87,000 psi is the maximum intensifier pump pressure. It has been proven that the fastest and most efficient cutting is done at the highest cutting pressure. While it is true than higher pressures can result in slightly increased maintenance on intensifier pump seals, for well designed equipment however, the very slight increase in maintenance cost is more than offset by the large increase in cut speed. Remember, the largest costs involved in abrasive waterjets are the labor, abrasive, and depreciation, not the pump seals.

How thick is the kerf?
The kerf is about 10% larger than the mixing tube diameter. So, for a 0.030″ mixing tube, the kerf will be 0.033″ Of course, the kerf will increase as the mixing tube grows. Tube growth is about 0.001″ per 8 hours of jet-on time.

What taper can I expect?
With a Dynamic Waterjet system, you will experience virtually no taper. In the case of conventional waterjet cutting, the taper you get is a function of the cut speed. However, the worst taper you will get will be equal to the maximum kerf width at the top (example: 0.035″) and 0.000″. at the bottom. As you slow down the taper will be reduced until you get parallel sides. Most tapers you see on precise cuts are 0.002″ to 0.004″ on a side.

How much water will you use when cutting at 55,000 psi? Each 0.010″ orifice uses 0.5 gpm. Each 0.013″ orifice uses 0.82 gpm Each 0.016″ orifice uses 1.24 gpm

How long before maintenance is required on the pump? You can expect around 400 to 1200 hours of cutting time before needing to replace the high-pressure seals on a 60,000 psi intensifier and 200 to 600 hours before needing to replace the seals in HyPlex direct drive pump.

What stops the jet?
In most waterjet systems 36 inches of water in the catchers dissipates the energy of the jet.

How long does the material support last? You can expect hundreds of hours of use from the support grating before needing to replace it, as long as you don’t cut just one pattern over the same section for thousands of parts. Slats and grates can be shifted, swapped, and flipped just as with plasma and laser cutting, thereby extending the life of the supports.

How long does the mixing tube last?
The highest quality ceramic carbide mixing tubes last 30% longer than other mixing tubes. A tube such as this can deliver 150 hours of cutting time for 0.020″ of growth in the diameter. Many users keep the mixing tubes longer and use them to cut parts which require looser tolerances.

How much abrasive is used?
For the most efficient cutting, cutting heads on a 60,000 psi intensifier use:

  • 0.010/0.030 0.9 lb/min
  • 0.014/0.040 1.4 lb/min
  • 0.018/0.050 2.5 lb/min

Do you have to pre-drill holes?
The waterjet can pierce the starting hole itself. In most materials, no special requirements are necessary. In some composites and brittle materials, lowering the pump pressure and/or using a vacuum assist piercing attachment is required.

I’ve heard that waterjets are hard to program. Is this true?
Waterjets are no harder to program with standard CNC equipment than any other cutting process. With standard CAM software, converting DXF to cutting program is quick and easy, with only speed changes for material changes. With the PC based control software such as FlowMaster, programming for abrasive waterjets is easier and quicker than any other process. All the guess work is gone. This means projects are programmed and cut quickly and accurately.

What fixturing is required?
Since the force exerted on the workpiece is very small (under 1 lb. for precision cuts and under 5 lbs. for average cuts), the need for very large, stiff fixtures is eliminated. Many customers use simple weights to hold the parts in place.