What is a Waterjet Cutter?
Waterjet cutting is simply an accelerated manufacturing erosion process within a selected material. Highly pressurised water is fired through a ruby or diamond nozzle into a mixing chamber.
This pressure creates a vacuum and draws garnet sand into the stream where it is then fired at the object in place for cutting.
The sand particles eat away at the material causing the effect of erosion to take place at such a high speed it is deemed as cutting.
This has allowed waterjet cutting to become an extremely powerful and versatile machining process that is used in many industries around the world.
A waterjet cutter is an industrial machine that is made up of three main components to utilise a high-pressure stream of water to erode a narrow line within a piece of material.
Depending on the material’s density and compound such as titanium a granular abrasive is added to the waterjet to increase the cutting power.
The abrasive is added at the nozzle so that a simple switch between only water and abrasive cutting can be made.
How Water Jet Cutting Works
A high-pressure water pump pressurises the water. This water flows through high-pressure tubing into the cutting head.
In the cutting head, the water flows through a nozzle, turning it into an extremely fine stream. This stream cuts whatever material is placed in front of it.
The water jet cutting process can be carried out in various ways, with most methods incorporating an abrasive into the water to facilitate cutting through the workpiece.
This versatile manufacturing technique can cut, shape, and design a workpiece to meet precise specifications.
The shaping method used in water jet cutting offers several advantages over other cutting processes like plasma or laser cutting.
Water jet cutting provides superior accuracy, can handle complex designs, and is suitable for thermally sensitive surfaces.
The abrasive, akin to sandpaper, erodes the material being cut without heating it or altering its temper. As a result, the cut edges are clean and ready for welding without the need for additional processing.
The Process of Water Jet Cutting
Measuring Kerf Width
Kerf width refers to the material removed during a cutting process. Traditionally, this term described the material removed by a saw blade.
In the context of a water jet cutter, kerf width denotes the width of the water stream, typically 0.04 inches or smaller. The inside corners cut by water jet cutting have a radius matching the stream’s width.
Several factors influence the kerf, including material thickness, type of material, cutting quality, and the characteristics of the waterjet nozzle.
The size of the kerf is a crucial design factor that must be considered when determining the dimensions of the final product.
For instance, if the kerf is 0.042 inches, the dimensions of the final part need to be adjusted to account for the cutting width. Otherwise, the final part will be 0.042 inches off.
Initial Water Jet Piercing
The initial cut made by a water jet cutter, known as the pierce, is wider than the usual kerf. This first step in the water jet cutting process can be executed in various ways, including stationary, linear, circular, and low-pressure methods.
The choice of piercing method depends on the material being cut and the amount of scrap produced.
Tapering in Kerf Width
Tapering in water jet cutting refers to the difference in kerf width at the top and bottom of the cut. This process creates a V-shaped taper because the stream loses energy as it cuts deeper into the material, removing more material at the top than at the bottom.
Slow cutting speeds can result in a reverse taper, where the kerf width is wider at the bottom of the cut.
This occurs because more material is removed at the bottom than at the top. A reverse taper is often observed when cutting soft, pliable materials.
Barrel tapers occur when the cut is widest in the middle and narrower at both the top and bottom, typically when cutting extremely thick materials.
For many cutting applications, tapering is not a significant issue and can even be advantageous for certain tasks.
However, in precision tooling where cut pieces must fit together accurately, tapering can pose a problem and should be carefully considered.
Pressurizing the Water
Water can be pressurized using various methods, such as linear intensifiers and rotary direct drive pumps.
Both types of pumps incorporate a motor, water filters, control systems, and sensors to ensure optimal performance.
Linear intensifier pumps operate using pressurized hydraulic oil at 3,000 psi. A low-pressure oil pushes against a piston with a face area 20 times larger than that of the high-pressure plunger, which acts on the water.
This difference in size intensifies the pressure on the high-pressure plunger by 20 times, resulting in a final pressure of 60,000 psi.
A direct drive rotary pump operates without hydraulic oil. Instead, it uses an electric motor to rotate a crank that drives pistons to generate water pressure.
These pumps typically feature 30 hp motors and an inlet that supplies water directly to the pump.
High Pressure Tubing
The pressurized water from the pump is transported through high-pressure tubing to the cutting head. This tubing, known for its excellent yield and tensile strength, features an exceptionally smooth interior surface.
It is made from cold-worked stainless steel or thermoplastic pressure hose, available in sizes ranging from 0.25 inches to 0.563 inches, and comes in various lengths to accommodate different water jet cutter designs.
Water Jet Cutting Head
The pressurized water exits through the orifice of the cutting head, which is made of diamond, ruby, or sapphire with a hole smaller than the tip of a pin.
As the water flows through this tiny orifice, its velocity dramatically increases to over 90,000 psi or 2,500 mph.
The effectiveness of the cutting process is closely linked to the power supplied by the cutting head. With proper use, a precision tooling cutting head can last between 500 to 1,000 hours.
The image below shows two types of cutting heads: one for water-only cutting and another for water with abrasive.
The distinction between the two is evident in the red tube, which is used to transport the abrasive material to mix with the water stream.
Pure Water Jet Cutters
Pure water jet cutters are the original type of water jet cutting tools. They are preferred because they produce less moisture on the workpiece compared to contact methods, and they create a thin, precise stream ideal for detailed geometries with minimal material loss.
Pure water jet cutters use a cutting head with a jewel, though rubies are not suitable for use with pure water. The water stream travels at Mach 2 for 40,000 psi and Mach 3 for 60,000 psi.
Abrasive Water Jet Cutting System
In an abrasive water jet cutting system, an abrasive material is introduced into the cutting head, where it is mixed with the water stream.
This addition sharpens the stream, enhancing its cutting effectiveness. Abrasive water jet cutters can handle a wide range of materials, regardless of their hardness or thickness, making them versatile for various applications.
An abrasive water jet cutter accelerates abrasive material along with the water stream to erode the surface of the material being cut.
It is 1,000 times more powerful than a pure water jet cutter. The larger diameter stream can cut materials up to ten inches thick without generating heat or causing mechanical stress.
Types of Water Jet Cutting
The principle of water jet cutting is straightforward, relying on pressure, velocity, and an abrasive. While the core concept is simple, its applications are diverse and highly specialized.
Various techniques have been developed to address specific requirements across different industries and materials.
Water jet cutting can be categorized into two main types: pure water and abrasive water jet cutting. Each of these categories can be further subdivided based on specific factors, including the material being cut, the desired precision, and the complexity of the cut.
Water Jet Cutting Types
Abrasive Flow Machining (AFM)
Abrasive flow machining (AFM) is used for interior surface finishing, particularly for deburring and honing parts that are difficult to reach with traditional methods.
By using a mixture of water and abrasive, AFM effectively erodes raised surfaces inside a workpiece, similar to the action of a grinder or sandpaper, to remove unwanted particles and achieve a smooth finish.
Abrasive Jet Machining
The abrasive jet machining process is a key aspect of abrasive water jet cutting. It involves a high-pressure stream of water mixed with abrasive particles that blast and erode the workpiece, removing particulate matter, burrs, and other materials.
This technique uses extremely fine particles applied at high velocity and is particularly effective for cutting and shaping brittle, thin, and hard materials. Abrasive jet machining excels in creating intricate shapes and achieving smooth, even edges.
High Pressure Water Cutting
Intensifiers are used to dramatically increase the pressure of pure water, allowing it to shape and form soft materials without leaving behind water residue.
Hydraulic pumps play a crucial role in this process, converting the force of the water into mechanical energy to achieve the required high pressure.
A significant advancement in high-pressure water jet cutting was the introduction of corundum elements in the cutting head, including varieties such as rubies and sapphires.
Corundum is renowned for its hardness, toughness, and stability, being resistant to acids and the second hardest mineral on Earth.
CNC Water Jet Cutting
CNC water jet cutting utilizes high-pressure water in a programmable manner to perform multiple operations in a single pass.
It is particularly useful for materials that are sensitive to high-temperature processes. CNC water jet machines can handle various operations such as cutting, forming, deburring, reaming, and honing, making them ideal for tasks requiring precision and minimal thermal impact.
Most CNC water jet cutting machines operate on three axes: X (left to right), Y (front to back), and Z (up and down). Recent advancements include five-axis models that add rotational capabilities.
The A axis allows rotation around the X axis, and the B axis provides rotation around the Y axis, offering greater flexibility and precision in cutting complex shapes.
Waterjet Cutting Materials
The process is compatible with a wide range of materials. In this section, we shall take a look at the different types of materials that can be cut effectively using a water jet cutter. We’ll cover:
- Metals
- Wood
- Rubber
- Ceramics
- Glass
- Stone and tiles
- Food
1. Metals.
The high velocity and pressures in waterjet systems make them capable of cutting thin and thick metals with relative ease.
This process is capable of cutting extremely hard materials such as titanium and Inconel along with common metals such as aluminium and mild steel.
The process is mainly used to cut thicker workpieces that can’t be cut with laser or plasma. For thinner metals, laser cutting has an edge over waterjet in terms of cutting speed.
A waterjet cutter with a 30 HP pump can cut 12 mm titanium at a rate of 180 mm/min.
For metals, waterjet provides the advantage of no HAZ formation which improves the final quality of a part significantly.
There is also no need for secondary finishing in most cases as this process provides satin-smooth edges.
Waterjet cut metal parts have high quality and are thus used in the most demanding sectors such as the aerospace industry that have no margin of error.
2. Wood.
A decent waterjet cutting machine can effectively cut wood up to 125 mm in thickness at a rate of up to 15 m/min. It can be used to split wood as well as to carve intricate shapes.
Moreover, the stream passes the wood at such a high speed that it causes virtually no surface wetness.
This prevents the wood from absorbing the water. The high pressure also causes minimal delamination.
However, the machine may have to be recalibrated if there are knots in the wood. Either we can use a higher pressure that can cut through the knots along with non-knotted areas or use different pressures for different areas. Using either option can affect the final quality of the part.
3. Rubber.
Waterjet technology is also increasingly used to cut rubber with varying thicknesses. A key advantage of a waterjet cutter is that it does not create concave edges, unlike die-cutting.
The technology is also not limited by the thickness of the rubber. The abrasive waterjet machine can cut rubber of varying hardness and thickness to the desired final quality.
In many cases, pure water jet cutting may be enough to meet product specifications for rubber products.
Pure water jet cutting can easily cut sponge rubber of up to 50 mm thickness and hard rubber greater than 25 mm thickness up to a bidirectional tolerance of 0.25 mm.
4. Ceramics.
Waterjet technology is commonly used in industrial cutting devices for ceramics. Ceramics are hard and brittle and difficult to machine.
They cannot withstand the excessive pressure that a workpiece is subjected to in other mechanical cutting methods.
In waterjet cutting, no excessive pressure is applied to the workpiece except at the cutting point. This makes it ideal for cutting ceramics. The cutter can pierce its own starting hole and precisely cut complex shapes.
CNC (computer numerical control) technology is used in conjunction with abrasive waterjet cutting to ensure repeatable accuracy and good edge quality.
5. Glass.
Waterjet cutting can cut a variety of glass with incredible detail. It can cut the most delicate glass without cracks or craters on it. On the other end of the spectrum, you may use it to cut stained glass.
Cutting with a waterjet does not require etching or breaking. But starting holes are pierced at a lower pressure due to the tendency to crack.
A waterjet can cut up to 50 mm of bulletproof glass, this number is even greater for other types of glasses.
6. Stone and tiles.
Stone and tiles are another common application for waterjet cutters. With the right technical settings, we can use a waterjet cutter for cement, ceramic, glass, granite, limestone, mosaic, metal, porcelain, travertine and quarry tiles.
7. Food.
Waterjet cutting is extensively used in the food industry because of the sanitation and productivity advantages it offers.
The USDA also approves its usage as the process does not contaminate the food with bacteria or other contaminants.
The waterjet executes precise cutting and portioning of small and large food items such as candies, pastries, poultry, fish and frozen foods.
Waterjet vs Other Cutting Methods
Waterjet has quite a few advantages over other cutting methods. In this section, we shall compare waterjet to other methods such as wire EDM (electric discharge machining), laser and plasma cutting on the following fronts.
- Material thickness
- HAZ formation
- Part tolerance
- Operation setup
1. Material thickness.
Waterjet can cut through 300 mm thickness of virtually any material (up to 600 mm for some).
Laser cutting is used for metals up to 25 mm in thickness (less for certain materials) excluding reflective metals, whereas EDM works only with conductive materials under 300 mm of thickness. Plasma can cut almost all metals with thicknesses up to 50mm (75 mm for some).
Flame cutting (oxy-fuel cutting) is another alternative that can accommodate metals up to 150 mm but it has certain limitations.
Cutting aluminium and copper alloys is not feasible and the edge quality is strongly in the waterjet’s favour.
Waterjet cutting is almost always the preferred choice when the material thickness is high and/or superior edge quality is a requirement.
2. HAZ formation.
Waterjet creates no HAZ whereas EDM’s HAZ is very shallow. Laser and plasma cutting can have significant HAZ depth depending on the gas used in the process. This makes post-processing necessary to remove HAZ and any other distortions. This is the main reason why waterjet gives the best edge quality right off the table.
3. Part tolerance.
Laser and EDM can match the waterjet’s tolerance specifications at 0.025 mm. Plasma can only give an accuracy of up to 0.25 mm. Cutting speed can affect this aspect though. As the speed increases, the machinable tolerances reduce.
4. Operation setup.
The setup for the waterjet machine remains relatively the same no matter the material. All other compared methods require different setups for different jobs and may even require different consumables.
Advantages of Waterjet Cutting
If we were to say that the waterjet cutting process is better than any other cutting method, it would not be an exaggeration or an overstatement.
Here are some of the benefits that the waterjet cutting process has to offer:
1. Superior Edge Quality.
One of the major reasons that professionals choose waterjet cutting is because of the edge quality it provides. Waterjet cutting is accomplished by hitting a very narrow beam of water on the workpiece.
Therefore, there are no metal cutters grinding against our object. This leads to a clean finishing and a superior edge quality.
2. Efficient.
Many people don’t know this about waterjet cutting- you can cut multiple layers of material at the same time by placing them on top of each other.
This process is called stacking and it makes waterjet cutting more efficient than any other cutting method.
For instance, in the amount of time it would take to cut one layer of stone slab for a kitchen, you could cut six layers on a waterjet cutter.
Therefore, the cost and time would be almost one-third, making the process very efficient and economical.
3. No Thickness Limitation.
Traditional cutting methods have a limitation on the thickness of material that you can cut. However, in waterjet cutting, there are no such limitations.
You would be surprised to know that in special mining applications, waterjet cutting is used to cut 100 feet of material thickness. Check our dedicated article for more information on how thick can a waterjet cut.
4. Better Accuracy, Low Cutting Tolerances.
Cutting tolerance is the shift in the position of the cutting process from the intended cut. In simple terms, cutting tolerance dictates how accurate (or how inaccurate) the cutting process is.
The lower the tolerance, the higher the cutting accuracy.
Waterjet cutting has one of the lowest tolerances out there. A major reason for this is that the cutting action is achieved through a very narrow beam of water.
Another important reason is that waterjet cutting is a cold cutting process, so no melting away of materials takes place.
5. Multiple Cut Shapes.
With waterjet cutting, you aren’t limited to cutting in straight lines. You can create multiple cut shapes in the workpiece in addition to the standard straight-line cuts.
Good waterjet cutters like the ones provided by Techniwaterjet even come with a range of complementary software with a lot of different preloaded cut shapes.
6. Multi-axis Cutting.
Besides offering different cut shapes, waterjet cutting is also a multi-axis cutting method. With a good waterjet cutter, you can cut in five different axes.
This helps in creating intricate parts such as small components of engines. 5-axis waterjet cutting is superior to the conventional 3-axis technologies due to a number of benefits like flexibility, cutting speed, and less manual labor required.
7. No Heat Affected Zones.
As mentioned earlier, waterjet cutting is a cold cutting method, so there is no temperature rise in the cutting points.
With temperature rise, the formation of heat-affected zones takes place where the characteristics of the material at the cut location change significantly.
8. Consistent Tooling.
With waterjet cutting, you don’t need to change your tooling when you insert a new workpiece or even a new material.
With a new workpiece of the same material, you don’t even need to change any settings. For new materials, you can adjust the settings with the software itself.
9. Material Integrity.
Since waterjet cutting creates no heat-affected zone, it preserves the integrity of the material throughout the workpiece.
The physical and chemical characteristics of the workpiece material will be the same at the cut location as it is elsewhere.
10. No Secondary Finishing Requirement.
Waterjet cutting leaves no visible stains on the material and has a high finishing. Therefore, you do not need any secondary finishing for the workpiece.
11. Environmentally Friendly.
Waterjet cutting follows a closed-loop process where all the water that you use for the cutting is recycled in the process itself.
The metal that is cut is strained through the water and sold as scrap. Therefore, it is a very environmentally friendly process.
12. Range of Supported Materials.
Waterjet cutters can cut through virtually any material, literally. This is quite a unique benefit of waterjet cutting.
Most of the other cutting methods apply to cutting only metals. However, waterjet cutting can cut through even wood, glass, or any other material.