What Is Waterjet Cutting?
Waterjet cutting is a highly versatile fabrication method that uses a high pressure stream of water— usually mixed with an abrasive media—to cut a wide range of materials into custom shapes and designs. Compared to other cutting processes, such as plasma or laser cutting, it offers a number of advantages, including the accommodation of more complex part designs as well as the ability to cut thicker or thermally sensitive materials.
Overview of the Waterjet Cutting Process
While waterjet technology is used in many specialized operations, in manufacturing, the term waterjet cutting is used to describe a computer-controlled (CNC) cutting machine which has a table for supporting the material and a gantry mounted cutting head. Specialized software is used to control the movements of the cutting head. Waterjets can be configured in many different ways, but they all follow the same basic principles shown below:
- The water is pressurized using either an intensifier pump or a direct-drive pump, also called a crankshaft pump. These pumps are very specialized and are capable of producing extremely high pressures. Some hydraulic pumps are rated for pressures as high as 90,000 psi.
- The pressurized water travels from the pump to the cutting head through high-pressure tubing. At the cutting head, the water passes through an orifice, which is a hard jewel (usually diamond or some hard gemstone such as ruby or sapphire) with a very small hole in it. As the water passes through the orifice, the pressure is exchanged for velocity. An intensifier pump operating at 90,000 psi can generate an orifice velocity of nearly 2,500 mph.
- Directly below the orifice in the cutting head assembly is the mixing chamber and nozzle. The mixing chamber is where the abrasive media (usually garnet) is introduced into the stream of water. In abrasive waterjet cutting, it is really the abrasive that does the cutting. The water is used as a means to accelerate the abrasive particles. After the mixing chamber is the nozzle (or mixing tube) which concentrates the water and abrasive into a very fine stream capable of cutting nearly any material.
Waterjet Cutting Process Considerations
Abrasive Waterjet vs. Pure Waterjet
The majority of waterjet cutting operations mix an abrasive into the waterjet stream. Garnet, which is the most commonly used abrasive due to its hardness and its availability, is available in two different products: crushed and alluvial.
Crushed garnet is mined out of the earth and then crushed, producing sharp aggressive edges that are ideal for waterjet cutting. Alluvial garnet is found in natural deposits in river beds. This product is cheaper because it requires less processing, but its edges are smooth from tumbling in the river, making it less aggressive than crushed garnet. Many waterjet users feel that the cost benefits of using alluvial garnet outweigh the reduction in performance.
The use of an abrasive is not necessary for all waterjet cutting operations. Soft materials such as rubber and foam can be easily and accurately cut using only water. Pure waterjet cutting, as this process is called, typically uses a much smaller orifice, producing an extremely fine, nearly invisible stream of water. Pure waterjet cutting is ideal for soft materials because the ultra-fine stream of water creates a very clean cut while applying almost no pressure to the material.
Intensifiers vs. Direct Drive Pumps
Two different types of pumps are used in waterjet cutting: intensifier pumps and direct drive pumps.
Intensifier pumps use hydraulic oil to push a piston connected to a ceramic plunger which in turn pushes against the water. Because the face area of the piston is 20 to 30 times greater than the face area of the plunger, the plunger creates a water pressure that is 20 to 30 times greater than the pressure of the oil. Intensifiers are the most commonly used type of waterjet pump, partly due to the fact that intensifier pumps are capable of producing much higher pressures than direct drive pumps. Intensifiers are less efficient than direct drive pumps and the higher pressures that they create shorten the lifespan of high-cost consumable parts. However, higher pressure directly translates to higher cut speeds and lower abrasive consumption, making hydraulic intensifiers a very viable option in many waterjet cutting applications.
Direct drive pumps—also known as crankshaft pumps—feature a crankshaft and piston design similar to the design of an automobile engine. An electric motor is used to drive a crankshaft connected to three or more reciprocating pistons which also use ceramic plungers to displace the water. In this way, a direct drive pump operates under the same basic principle as an intensifier pump, the only real difference being the method used to move the pistons. Direct drive pumps are inherently more efficient at turning power into pressure, losing much less energy in the form of wasted heat. However, they are limited to 60,000 psi, whereas intensifier pumps can produce pressures as high as 90,000 psi. In spite of this limitation, direct drive pumps remain popular and are preferred in some applications.
Dynamic Taper Compensation
One of the greatest advancements in waterjet cutting technology came with the introduction of dynamic taper compensation. Dynamic taper compensation solves the greatest drawback inherent to waterjet cutting—taper. The waterjet stream is a flexible tool, meaning that it is not rigid like a milling machine cutter or router bit, but rather has the ability to be deflected. As the waterjet stream cuts through the material, it fans out behind the leading edge of the stream, becoming much narrower on the exit side of the material. This narrowing of the stream produces a tapered cut which is usually considered undesirable. The higher the cut speed, the more the bottom of the stream drags behind the top, producing more taper. Additionally, faster cut speeds result in a rougher cut quality. As the stream becomes narrower and drags behind, it loses its energy and begins to waver, producing striations in the bottom edge of the cut.
Without taper compensation, the only way to reduce taper is to slow down the cut speed. The slower the cut speed, the less the stream deflects. Using this method to eliminate taper is very cost prohibitive because the part takes so much longer to cut, greatly increasing the inputs and the amount of time on the machine. Waterjet machines equipped with dynamic taper compensation utilize very complicated software programming to calculate exactly how much to tilt the head to completely eliminate taper. As the machine accelerates and decelerates, the head has to change its angle accordingly. The best taper control systems also tilt the head forward to counteract the drag of the waterjet stream. Dynamic taper compensation takes all of the fine nuances of the waterjet cutting process into consideration, making it possible to cut parts both accurately and economically.
5-Axis Waterjet Cutting
Another major improvement in the world of waterjet cutting came with the advent of 5-axis waterjet technology. In reality, 5-axis waterjets have been around for quite a long time, but up until the last decade or so, they were very cumbersome machines that were much too complicated to be useful in a job shop. Their use was reserved for high production applications or extremely specialized parts, which can justify great amounts of programming time.
Today, 5-axis waterjets are capable of taking a 3D model from CAD programs and creating a cut program within minutes. The actual setup and process can still be much more complicated than in regular 2D cutting, making it still a somewhat specialized process. Nevertheless, in many cases, 5-axis waterjets are able to produce parts quickly and cost-effectively that would be very costly and time consuming to produce using conventional machining methods.
Industries Served by Waterjet Cutting
Waterjet cutting is a highly accurate and reliable process that can be used in the manufacturing of a variety of parts and components for a diverse set of industries, including the following:
Products Manufactured by Waterjet Cutting
Parts and products produced through the waterjet process vary greatly in regard to material, size, shape, complexity, and use. Some examples of products that utilize waterjet cutting are:
- For the aerospace industry: structural panels and brake, wing, and turbine components
- For the architectural industry: decorative panels and exterior building facade components (e.g., panels)
- For the automotive industry: body and insulation components
- For the electronics industry: circuit boards, panels, and enclosures
- For the food industry: vegetables, meats, and cakes
- For the manufacturing industry: valve bodies, sheet metal patterns, and heat exchanger tube sheets
Expert Waterjet Cutting Services from AquaJet Services
AquaJet Services is a family-owned business offering custom waterjet cutting and fabrication services to the industrial sector. Our facility is equipped with 5-axis waterjets that offer the highest cutting precision and pressures available. This equipment accommodates a wide range of materials—from metal to plastic and rubber to brittle ceramics, glass, and stone—in thicknesses of .001” to 16 inches or more.
By partnering with us for their waterjet cutting needs, our customers benefit from our:
- 15 years of industry experience
- Advanced waterjet cutting equipment, including state-of-the-art, 5-axis waterjets
- Full-service solutions, including custom design and fabrication
- Honest and fair pricing
- On-time and rush delivery services
For more information on our waterjet cutting services, contact us today.