What Is Waterjet Cutting?

Waterjet cutting is a versatile cutting method that uses a high-pressure stream of water—usually mixed with an abrasive media—to cut a wide range of materials into shapes and designs. Compared to other cutting processes, such as plasma or laser cutting, it offers several advantages, including better accuracy, the accommodation of more complex part designs, and 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 that 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:

1. The water is pressurized using either a hydraulic 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 intensifier pumps are rated for pressures as high as 90,000 psi.
2. 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 a diamond, ruby, or sapphire) with a hole in it that is smaller than a pinhole. As the water passes through that tiny hole, its pressure is exchanged for velocity. An intensifier pump operating at 90,000 psi can generate an orifice velocity of nearly 2,500 mph.
3. Most waterjets have a mixing chamber and nozzle directly below the orifice in the cutting head assembly. The mixing chamber is where the abrasive media (usually garnet) is drawn into the stream of water. In abrasive waterjet cutting, the abrasive does the cutting, and the water is the means that accelerates the abrasive particles. Below the mixing chamber is the nozzle (or mixing tube) in which the water accelerates the abrasive, forming a fine, sharply defined 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 media into the waterjet stream. This type of waterjet cutting is used for all hard materials—metals, glass, stone, etc. The most commonly used abrasive is garnet due to its hardness and availability. It is available in two different products: crushed and alluvial.

Crushed garnet is mined in quarries and then crushed, producing sharp aggressive edges that are ideal for waterjet cutting. Alluvial garnet is found in natural deposits in riverbeds and is simply cleaned and screened. This product is cheaper because it requires less processing, but its edges are smoothed by natural erosion, 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. Materials that are soft enough to be cut with a knife, 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 hydraulic piston is 20 to 30 times greater than the face area of the ceramic plunger, the plunger creates a water pressure that is 20 to 30 times greater than the pressure of the hydraulic oil. Intensifiers are the most commonly used type of waterjet pump, partly because 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 layout 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 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. Despite this limitation, direct-drive pumps remain popular and are preferred in some applications.

Taper Compensation

One advancement in waterjet cutting technology came with the introduction of taper compensation. Taper compensation corrects the greatest limitation in accuracy inherent to waterjet cutting. The waterjet stream is flexible—not rigid like a milling machine cutter or a saw blade—so it can be deflected. As the stream cuts down through the material, it fans out behind the leading edge of the stream, while narrowing in width. This narrowing of the stream produces an undesirable taper in the cut. The higher the cut speed, the more the bottom of the stream trails back and narrows, producing more taper. Additionally, faster cut speeds result in a rougher cut quality. As the stream becomes narrower and fans backward, 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 increases cost because the part takes much longer to cut, greatly increasing the inputs and the amount of time on the machine. However, this problem is solved in waterjet machines equipped with taper compensation by utilizing complex software programming to calculate exactly how much to tilt the head to eliminate taper on the part side of the cut. This leaves all of the taper on the scrap side of the cut. As the machine accelerates and/or changes direction, the head changes its angle accordingly. The best taper control systems also tilt the head forward to counteract the drag of the waterjet stream. Taper compensation takes the fine nuances of the waterjet cutting process into consideration, making it possible to cut parts both accurately and economically.

One interesting capability of waterjet cutting combined with taper compensation is that thin materials can be cut very cheaply and accurately through stacking. For example, a stack of 50 sheets of 0.005” thick shim stock cuts at exactly the same speed as a 1/4” thick plate, and all of the finished sheets are identical.

5-Axis Waterjet Cutting

Another improvement in the world of waterjet cutting came with the advent of 5-axis waterjet technology. Actually, 5-axis waterjets have been around for quite a long time, but up until 2010 or so they were too cumbersome and expensive to be useful in the job shop market. Their use was reserved for high-production applications or extremely specialized parts which could 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. In order to do 5-axis cuts accurately, the setup and process are much more exacting than in regular 2-axis cutting, so it remains a specialized process. Nevertheless, in many cases 5-axis waterjets can 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:

• Aerospace
• Architecture
• Automotive
• Electronics
• Food
• Manufacturing

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:

• Aerospace industry: metal or composite components in fuselages, wings, and turbines
• Architectural industry: decorative panels and exterior building facade components
• Automotive industry: body and interior components
• Electronics industry: circuit boards, panels, and enclosures
• Food industry: vegetables, meats, candies, and cakes
• Manufacturing industry: shapes in sheets and plates, sheet metal patterns

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 metals, plastics, and rubber to ceramics, glass, and stone—in thicknesses from .001” up to 18” 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
• Comprehensive design services
• Full-service solutions, including custom design and fabrication
• Honest and fair pricing
• On-time and rush delivery services
• Eagerness to be challenged by jobs with unusual requirements

For more information on our waterjet cutting services, contact us today.