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What is waterjet

Waterjet is a tool capable of slicing into metal or other materials using a jet of water at high velocity and pressure, or a mixture of water and an abrasive substance. The process is essentially the same as water erosion found in nature but greatly accelerated and concentrated. It is often used during fabrication or manufacture of parts for machinery and other devices. It is the preferred method when the materials being cut are sensitive to the high temperatures generated by other methods. It has found applications in a diverse number of industries from mining to aerospace where it is used for operations such as cutting, shaping, carving, and reaming.

With waterjet machining, a flat piece of material is placed on a table and a cutting head moves across the material (although in some custom systems, the material moves past a fixed head). This simplicity means that it's fast and easy to change materials and that no tool changes are required. All materials use the same cutting head, so there is no need to program tool changes or physically qualify multiple tools.

The movement of the machining head is controlled by a computer, which greatly simplifies control of the waterjet. In most cases, "programming" a part means using a CAD program to draw the part. When you "push print," the part is made by the waterjet machine. This approach also means that customers can create their own drawings and bring them to a waterjet machine for creation.

What little heat is generated by the waterjet is absorbed by the water and carried into the catch tank. The material itself experiences almost no change in temperature during machining. During piercing 2" (5 cm) thick steel, temperatures may get as high as 120° F (50° C), but otherwise machining is done at room temperature.

The result is that there is no heat affected zone (HAZ) on the material. The absence of a HAZ means you can machine without hardening the material, generating poisonous fumes, recasting, or warping. You can also machine parts that have already been heat treated.

The amount of material removed by the waterjet stream is typically about 0.02" (0.5 mm) wide, meaning that very little material is removed. When you are working with expensive material (such as titanium) or hazardous material (such as lead), this can be a significant benefit. It also means that you can get more parts from a given sheet of material.

When comparing with lasers:

Can work with more materials
Waterjets can machine reflective materials that lasers cannot, such as copper and aluminum. Waterjets cut a wide range of material with no changes in setup required. Also, materials which are heat-sensitive can be cut using waterjets.

No heat-affected zone (HAZ) with waterjets
Waterjet cutting does not heat your part. There is no heat-affected zone (HAZ) or thermal distortion, which can occur with lasers. Waterjets do not change the properties of the material.

Waterjets are more environmentally friendly
Abrasivejets typically use garnet as the abrasive material. Garnet is a non-reactive mineral that is biologically inert. The only issue with waterjets is when you are cutting a material that is potentially hazardous (such as lead), since small pieces of the material will be abraded and mix in with the spent garnet.

Waterjets are safer
There are no noxious fumes, such as vaporized metal, and no risk of fires. The distance between the end of the waterjet nozzle and the material is typically very small, although caution is needed when the waterjet nozzle is raised.

Uniformity of material not important
With lasers, the material needs to be relatively uniform. In particular, when cutting over uneven surfaces, the laser can lose its focus and cutting power. A waterjet will retain much of its cutting power over uneven material. Although the material may deflect the cutting stream, it typically has a negligible effect.

Lower capital equipment costs
The cost of a waterjet machine is generally much lower than that of a laser. For the price of a laser, you can purchase several waterjet machining centers.

Better tolerances on thicker parts
Waterjets offer better tolerances on parts thicker than 0.5" (12 mm). For thinner parts, both waterjets and lasers offer comparable tolerances.

Waterjets can machine thicker materials
How thick you can cut is a function of how long you are willing to wait. Waterjets easily handle 2" (5 cm) steel and 3" (7.6 cm). Although some people have used waterjets at thicknesses of up to 10" (25 cm) in steel, it is difficult to maintain precision in materials thicker than  2" (5 cm). Lasers seem to have a maximum practical cutting thickness of 0.5" (12 mm) to 0.75" (19 mm).

Simpler maintenance
Maintenance on a waterjet is simpler than that of a laser.

Simpler operation
Waterjets are computer controlled, so that the operator does not have to be highly skilled and trained. 

Better edge finish
Material cut by waterjets have a fine, sand-blasted surface because of the way the material was abraded, which makes it easier to make a high-quality weld. Material cut by laser tends to have a rougher, scaly edge, which may require additional machining operations to clean up.

When comparing waterjet cutting with EDM:

Abrasive jets are much faster than EDM, which slowly removes the metal.

Can work with more materials
Waterjets can machine non-conductive materials that EDM cannot, such as glass, wood, plastic, and ceramic. There is almost no limit to the type of materials that can be machined with waterjets.

Uniformity of material not important
A waterjet will retain much of its cutting power over uneven material. Although the material may deflect the cutting stream, it typically has a negligible effect. Such material aberrations would cause wire EDM to lose flushing.

Waterjets make their own pierce holes
Some types of EDM, such as wire-cut EDM, a hole needs to be first made in the material, which has to be done in a separate process. Waterjets can pierce the material, requiring no additional fixturing or machining.

No heat-affected zone (HAZ) with waterjets
Waterjet cutting does not heat your part. There is no heat-affected zone (HAZ) or thermal distortion, which can occur with EDM. Waterjets do not change the properties of the material.

Waterjets require less setup
Most of the fixturing with waterjets is weighing down the material so that it does not shift in the water tank. The fixturing needs to withstand forces of pounds and does not need to be elaborate or precise.

Make bigger parts
The size of the part created with a waterjet is limited by the size of the material. In setups where the material passes underneath the waterjet, the finished part size can be huge. Even with an X-Y table setup, part sizes can be quite large.

When comparing waterjet cutting with plasma cutting

The clearest advantage that waterjets have compared with plasma cutting is that waterjets operate at much lower temperatures. During piercing, the temperature of the material may rise as high as 120° F (50° C), but cutting typically happens at room temperature. The presence of the catch tank (a large tank full of waste water) helps to moderate the temperature as well. This lower temperature means there is no Heat Affected Zone when material is cut with a waterjet.

Waterjets also can cut materials that don't easily melt (such as granite) or that are destroyed by melting (many laminates). Waterjets are also more precise than plasma cutting.
Plasma cutting is typically faster than waterjet, particularly with very thick metal. Plasma torches can pierce and cut steel up to 12" (30 cm) thick.

When comparing waterjet cutting with flame cutting

While flame cutting can work only with iron or steel, waterjets can machine many different types of materials, both metal and non-metallic. Waterjets also do not appreciably heat up the material they cut during piercing, temperatures may rise to 120° F (50° C), but during cutting the material is heated only a degree or two.

The edge finish created with a waterjet is smooth, similar to a sandblasted finish, rather than the rough edges left by flame cutting. Waterjets are more precise than flame cutting and have a much smaller kerf as less material is removed (particularly important when cutting expensive material).

Flame cutting can be faster than waterjets, especially when done using a multi-torch cutting machine, and as a result is cheaper than waterjet cutting.

When comparing waterjet cutting with milling

Although mills cut faster, in most cases, than waterjets, the setup and fixturing with waterjets is much simpler. Setup with waterjets is typically a matter of just loading the part drawing into the controller software, setting the material and thickness and beginning machining. Similarly, fixturing is mostly a matter of weighing down the material so that it doesn't move on the table during machining. Clean-up on a waterjet is also faster and simpler. As a result, overall, a waterjet can have a greater throughput than a mill on similar parts.

Waterjets can also machine almost any material, including brittle materials, pre-hardened materials, and otherwise difficult materials such as Titanium, Hastalloy, Inconel, SS 304, and hardened tool steel.

With a waterjet, there is also no tool changing. The waterjet nozzle is the only tool used, and it is used for all the different types of materials that a waterjet cuts. There is also less wear on tools, especiall in harder and gummier materials, because the cutting action of the waterjet is the stream of water and abrasive. While there is wear on the mixing tube and high-pressure water componenets, this wear tends to be constant with time, and doesn't change with different materials.

Waterjets are frequently used for complimenting or replacing milling operations. They are used for roughing out parts prior to milling, for replacing milling entirely, or for providing secondary machining on parts that just came off the mill. For this reason, many traditional machine shops are adding waterjet capability to provide a competitive edge.

When comparing waterjet cutting with punch preses

Waterjets have a lower cost-per-piece for short runs than a die press, because of the expense (and time) involved in creating the dies and punches. Creating the drawing for a part on a waterjet machine is all that's needed to begin machining the part, where with a punch press, the drawing is usually only the first step to creating the die.

Lateral forces wtih a waterjet are negligible, which means that holes can be placed very close to the material edge, which is not the case with a punch press. Waterjets can also work with very thick materials, while punch presses are limited in thickness to the amount of pressure they can apply. And, of course, waterjets can work with many different types of materials, including brittle materials and laminates.

Some stamping houses are using waterjets for fast turn-around and rapid prototyping work. Waterjets make a complimentary tool for punch presses because they offer a wider range of capability for similar parts. For high production of thin sheet-metal, the stamp will be more profitable in many cases, but for short runs, difficult material, and thick material, waterjets have their place.

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