Best of Both Worlds

Waterjet cutting uses a highly pressurized stream of water to fabricate parts from a variety of materials. It’s fast and…

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Waterjet cutting uses a highly pressurized stream of water to fabricate parts from a variety of materials. It’s fast and accurate but sometimes misunderstood. Among metal fabricators, waterjet cutting usually refers to abrasive waterjet cutting, a version of the process that mixes a garnet abrasive with a highly pressurized stream of water. Among rubber fabricators, however, waterjet cutting typically refers to pure waterjet cutting, which uses a highly pressurized stream of water without an abrasive material.

In general, pure waterjet cutting is used to process softer, thinner materials like rubber and plastic sheets. It can also be used with rubber and plastic extrusions, thermal and acoustic foams, thin metal foils and industrial fabrics. Abrasive waterjet cutting is used mainly for harder, thicker materials like metals and composites. It’s also used with ballistic steel and ballistic glass. In addition, abrasive waterjet cutting is used to process rubber products that contain metal inserts and to cut thicker, softer materials.

With both types of waterjet cutting, there is never any tooling to wait for or pay for. Because the equipment is computer-controlled, a parts fabricator can use an engineer’s CAD file to create a CAM file that controls the machine with precision. For fast cuts, smooth joints, clean edges and perfect 90-degree corners, waterjet cutting can support projects ranging from quick-turn iterative prototypes to low- to medium-volume production.

Waterjet cutting can be used for quick-turn prototyping and low- to medium-volume production.

For example, Elasto Proxy is a parts fabricator that uses pure waterjet cutting to convert acoustic foams into custom panels that conform to the contours of operator cabins. The company also uses abrasive waterjet equipment to make angled cuts with bulb trim, a rubber product that is reinforced with metal wire and installed on cabin doors with rounded corners. The heavy equipment industry doesn’t need acoustic insulation or door seals in high volumes, but fast and accurate cuts are a requirement.

Winning business

For shops that want to win new business and for customers that want greater value, abrasive waterjet cutting versus pure waterjet cutting doesn’t have to be an either/or proposition. Some equipment is capable of just one type of waterjet cutting, but there are also machines that can cut both with and without abrasive material. Today, there are parts fabricators that are using both processes to provide customers with a complete solution.

For example, consider the case of rubber and metal assemblies. Rubber can be molded over metal to form a permanent bond, but what if the rubber needs to be removable? With the right waterjet equipment, a fabricator can cut a metal arm, cut a rubber gasket and then assemble the gasket over the arm like a sleeve. A fabricator can also cut stainless steel for kitchen tables and then cut the rubber edge trim that is installed along the table’s edges.

With machines that support both abrasive waterjet cutting and pure waterjet cutting, adjustments need to be made when switching back and forth. Specifically, there are three key considerations: cutting heads, cutting surfaces and water pressure. It’s also important to perform regular cleanups and periodic maintenance.

Figure 1. Abrasive waterjet cutting requires a sand supply line and a cutting surface with metal slats.

Cutting heads and surfaces

Figure 1 shows a waterjet table configured for abrasive waterjet cutting. A special abrasive waterjet head is connected to a tube that supplies the abrasive material (i.e., sand). This material is stored in a pressurized reservoir that, depending on the size of the reservoir and the frequency of the equipment’s use, may need to be refilled daily. When it’s time to switch to pure waterjet cutting, an operator replaces this cutting head with one that doesn’t have a sand supply line.

Machines that are equipped for abrasive waterjet cutting and pure waterjet cutting also use two different cutting surfaces. In Figure 1, the red arrow shows how the waterjet table has metal slats with gaps of several inches between them. These slats form channels that hold the fluid slurry that is dispensed. Because the cutting head doesn’t remain in one position for long, abrasive wear on the slats is gradual. Eventually, however, the slats will become worn, chipped and require replacement.

When it’s time to switch to pure waterjet cutting, plastic supports are laid on the table in between the metal slats. In Figure 2, a red arrow points to these supports, which have small openings that allow the dispensed water to pass through. These support structures are necessary because pure waterjet cutting is generally used with softer materials. The harder and stiffer materials that are fabricated with abrasive waterjet cutting can sit atop the slats, but this doesn’t work with a thin, flexible rubber sheet.

This 6-axis robot combines freedom of movement with a 40-in.-by-60-in. work envelope for waterjet cutting.

Water pressure and cleanup

During waterjet cutting, a pump generates water pressure measured in tens of thousands of pounds per square inch (psi). Next, the waterjet cutter converts this pressure into velocity. Water then travels into the cutting head and through a jewel orifice that restricts the flow of this high-pressure fluid. Because there is no tooling to configure, the advantages of waterjet cutting include the elimination of setup charges. Still, it’s important to use the right psi for the specific cutting process.

For pure waterjet cutting, the water pressure ranges between 20,000 and 60,000 psi. That is a wide range, but the proper pressure depends on the fragility of the material being cut. With abrasive waterjet cutting, the pressure isn’t as material-dependent. Generally, it’s 60,000 psi.

Figure 2. Pure waterjet cutting uses a different cutting head than abrasive waterjet cutting and a cutting surface with plastic supports.

When a shop uses abrasive waterjet cutting, it’s typical for some dust residue to be left on and around the waterjet table. A quick cleanup is required, but is typically not extensive. Eventually, however, the table will fill with sand. That is when the fabricator needs a contractor with special siphoning equipment. The vacuum truck and heavy-duty hose that are used are not unlike what is required for cleaning chemical toilets. If the table is very full, the cleanup process may take all day. Strong suction is especially important because the abrasive material between the metal slats is more like quicksand than playground sand.

Advantages and applications

Waterjet equipment that supports both pure waterjet cutting and abrasive waterjet cutting can have three axes or six axes. Three-axis, gantry-style machines are ideal for small to medium-sized parts, including components with thin, tapered ends such as small hooks with bolt holes. Six-axis waterjet cutting uses an industrial robot that supports a larger work envelope and can cut larger parts. Applications include the ballistic glass for windshields on military vehicles.

atch the video to get a quick overview of Elasto Proxy’s approach to cutting without the need for tooling.

Compared to other types of cutting operations, waterjet cutting has distinct advantages. For example, the guillotine cutting used for rubber profiles with metal inserts can deform the rubber and produce cuts with inconsistent quality. Die cutting can also put pressure on a rubber profile and cause edge distortions, especially with softer elastomers. With metal parts, laser cutting can create heat-affected zones and cause material hardening. CNC cutting requires tooling and may also distort the workpiece.

For fabricators in search of new opportunities, and for customers that want shops that provide greater value, waterjet cutting is too important to overlook. Other cutting processes have their advantages, of course, but both pure waterjet cutting and abrasive waterjet cutting can produce high-quality parts quickly and cost-effectively. Plus, with equipment that supports waterjet cutting both with and without abrasive material, cutting dissimilar materials like metal and rubber is no longer an either/or proposition.

Elasto Proxy

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