Waterjet refers to an industrial tool that utilizes a high-pressure stream of water, or mixture of water and an abrasive substance, to efficiently cut a variety of materials. A waterjet machine typically consists of a controller that uses software to operate the system, a high-intensity pump, and a table with an x-y motion system, which is used to accurately move the nozzle to create the desired cutting path. A waterjet cutter’s high-pressure pump typically generates 40,000 PSI to 60,000 PSI. Two types of pumps are used to create this high pressure. An intensifier pump creates pressure by using hydraulic oil to move a piston, forcing the water through a tiny hole, while a crankshaft pump works much like a car engine, forcing water through high-pressure tubing using plungers attached to a crankshaft.
The water travels along high-pressure tubing to the waterjet’s nozzle, where it is then focused into a thin beam by a jewel orifice. When it ejects from the nozzle, the high-pressured water can reach an exit speed over Mach 3. At this intensity, water alone can cut plastics, foam, wood, resilient floor coverings, rubber, leather, textiles, gasket, and similar soft substances.
To cut a wider range of materials, water jetting’s effectiveness can be increased by the addition of an abrasive compound to the jet stream. The process for an abrasive waterjet is similar to a traditional waterjet up until the water reaches the nozzle. Here, the nozzle is often switched out for an abrasive cutting nozzle, which includes a mixing tube. The high-pressure waterjet creates a vacuum which pulls the abrasive into a mixing chamber, and then produces the intense abrasive waterjet stream.
Abrasive waterjet cutting is ideal for sheet metals, composites, stone, glass, and other hard materials. The most common type of abrasive used in waterjet cutting is red garnet. This gemstone material is fairly hard and when it fractures, it forms sharp edges, both of which are advantages in waterjet cutting. Garnet is also relatively chemically inert and won’t react with materials being cut, making it easy to dispose. Other abrasive types can used to save on cost, including a softer abrasive such as olivine. Softer abrasives can be beneficial as they reduce wear on the mixing tube.
The particle size of the abrasive material is measured by its mesh number. Mesh refers to the coarseness of abrasive used, with higher numbers being finer abrasive with smaller particles. For maximum cutting speeds, a coarser abrasive is used. Most abrasive waterjet applications use No. 80 mesh, but a finer abrasive such as No. 120 might be used for smoother surface finishes.
In waterjet cutting, the edge quality of the cut material is defined as quality numbers Q1 through Q5. Lower numbers indicate a rougher edge finish, while higher numbers are smoother. Q1 is the fastest cut and is described as a separation cut, Q2 a through cut, Q3 a clean cut, Q4 a good finish, and Q5 an excellent finish. By programing variable speeds into the job, a part can have multiple finishes, which can save on costs for large parts.
Unlike plasma cutting, waterjet cutting can cut materials that don’t easily melt or are destroyed by melting, such as laminates. It is also considered more environmentally-friendly, since no fumes or gases are released during the process, and there is no heat affected zone. While plasma cutting is typically more affordable than waterjet cutting, a waterjet cut is more precise and accurate.