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Waterjet cutting compared to other technologies

Why should I use waterjet cutting not 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.
* 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, you only have to change the cutting 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.
Why should I use waterjet cutting not EDM?
EDM is extremely accurate, but very slow. It also requires an electronically conducive material and produces a heat-affected zone.

Why should I use waterjet cutting not 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.Why should I use waterjet cutting not plasma or oxy fuel?
Visibly, 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.

Thickness of material and cutting accuracy in comparison - Laser / Plasma / EDM / Waterjet

The most common questions with corresponding answers

What tolerances can we expect from waterjet cutting?
Over 80% of the world's abrasive jet users cut parts to ±0.1mm or looser accuracy.

Should I cut underwater?
The biggest advantage of cutting under water is that it will reduce the noise of the cutting process to under 75 dBA.
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. Cutting performance will decrease for 5% when you cut 1mm under water.

How thick can it cut?
Up to 200mm thick steel and titanium are cut on a production basis. There have been cases where 300mm and even 400mm thick material has been cut. The vast majority of users, however, cut between 10mm to 60mm thick materials.

At what pressure do I cut?
420 MPa is the maximum intensifier pump pressure. It has been proven that the fastest and most efficient cutting is done at 380 MPa. Higher pressures results increased maintenance on pump seals.

How much water is used when cutting at 400MPa?


How thick is the kerf?
The kerf is about 15% larger than the mixing tube diameter. So, for a 0,8mm. mixing tube, the kerf will be 1,0mm. Of course, the kerf will increase as the mixing tube grows.

What taper can I expect?
The taper you get is a function of the cutting speed. However, the worst taper you will get will be equal to the maximum kerf width at the top (example: 0.8 mm) and 0.0mm 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 0.05mm to 0.10mm on a side.

Do you have to pre-drill holes?
The water jet 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.

What stops the jet?
In most waterjet systems 700 mm of water in the catchers dissipates the energy of the jet.

Quality of water
The following water quality is required for the operation of a waterjet system:

* pH value 7,0 - 8,5
* Carbonate hardness 20 - 60 ppm corresponds to 2 - 6 ° dH
* Calcium carbonate (Ca) 35 - 107 ppm
* Chloride content (Cl) ? 100 mg/l
* Inlet temperature for feed-water 10 - 25 °C
* Electrical conductivity at +25°C ? 450 µS/cm
* Dry residue of filtrate. ? 350 mg/l
* Free, dissolved chlorine ? 1 mg/l
* Feed-water pre-pressure 0,2 - 2,5 MPa
Deviations from these values lead to shorter serviceable lives of the high-pressure gaskets of the pump and of the nozzles. Therefore, we recommend a water analysis and, if necessary, a corresponding water conditioning.

Power supply
For each installed abrasive cutting head an electric load of 37 kW has to be considered.

When do I use more than one cutting head and how does it work?
More than one cutting head is used when many equal shaped parts have to be produced.
Either a second cutting head is installed on the existing z-axle or a second z-axle is installed that can carry more than one cutting head. To realise a constant cutting performance it is important that every single cutting head is supplied with the same pressure and the same rate.

How long before maintenance is required on the pump?
The high-pressure seals shall be changed as soon as they leak! At a constant operating pressure of 400 MPa the seals have to be changed after 400 to 1200 hours of cutting time.

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

How much abrasive is used?
For the most efficient cutting, cutting heads on 400 MPa use:
* orifice 0.15 mm / focus 0,6mm 150g/Min
* orifice 0.25 mm / focus 0,8mm 350g/Min
* orifice 0.35 mm / focus 1,0mm 450g/Min

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. 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?
Good ceramic carbide mixing tubes (focus) last 100 hours. 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 0.5mm of growth in the diameter. Many users keep the mixing tubes longer and use them to cut parts which require looser tolerances.

How long does the orifice last?
A sapphire orifice last 25 hours. The highest quality diamond orifice lasts much longer but costs about 30-times more and is normally used for pure waterjet cutting.

Are Waterjets easy to program?
Water jets 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 Windows based control software such as EasyCut, programming for abrasive water jets 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 work piece is very small (under 1 Kg. for precision cuts and under 5 Kg for average cuts), the need for very large, stiff fixtures is eliminated. Many customers use simple weights to hold the parts in place.

Costs, Safety and Environmental concerns

Costs
How much do people charge for waterjet services?
Abrasive waterjet shops typically charge Euro 120 - 220 per hour for their services.
What are the operating costs of a waterjet?
Hourly costs range from about Euro19/hr for the small head (orifice 0.15 mm/ focus 0,6mm), up to Euro 35/hr for the large head (orifice 0.35 mm/ focus 1,0mm). This includes all costs related to the machine, but does not include labor, lease, and depreciation.

What is the cost of the abrasive?
Abrasive will cost between Eur 280 and Euro 300 /ton ex works A-5500 Bischofshofen.

Safety
What happens if I stick my finger in there?
It will get cut. However, the industry is very conscience of and proactive in the safety of its equipment. Consequently, abrasivejet users actually have a better safety record than most machine tool users.

How loud is it?
Noise from the waterjet is dependent upon the distance the supersonic jet is exposed to the open air. If you are cutting underwater, the noise level will be less than 75 dBA. If you are cutting above water, and especially if there is a large distance between the focus and the work piece, the noise will be much higher, up to 105 dBA. In these cases, most customers enclose the entire work area.

Environmental Concerns

How do we dispose of water/garnet?
Neither water nor garnet are toxic or hazardous in any way. The water, when properly filtered for turbidity, can be put down the drain. The garnet waste can usually be dumped in a standard landfill. Of course, if the material you are cutting is toxic or hazardous, the waste generated may be hazardous.
Please see your local utilities for specific requirements.

Is this pure water?
It is clean water. Most of our customers use softened tap water. Intensifier pumps should be supplied with filter cartridges that clean the water down to 0.5 micron. De-ionized or reverse osmosis systems are generally not recommended. These types of systems can make the water too clean, which makes the water aggressive and harmful to the pump.

Can I recycle the water?
Closed-loop, recycling systems are available. However, because waterjet systems use a low amount, approx. 200 l/hour, of water it is not economically viable for most users.

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