What is Waterjet Cutting?

Waterjet cutting may be a simple machining method, but it packs a powerful punch. To learn more about this cutting process, keep on reading.

Waterjet Mechanics

All waterjet machines have a pump that pressurizes the water before delivery to the cutting head, where it’s converted to a supersonic stream. However, there are two types of pumps that exist: direct-drive based pumps and intensifier-based pumps. Each of which perform the same job, but the method of doing so is slightly different.

Direct-drive pumps act like a pressure washer, with a triplex pump that triggers three plungers directly from the electric motor. The maximum continuous operating pressure is around 10 to 25% lower than intensifier pumps, though this still puts them between 20,000 and 50,000 psi.

As for intensifier-based pumps, they make up the majority of pumps over 30,000 psi. These pumps contain two fluid circuits, one for water and one for hydraulics. The inlet water filters take in ordinary tap water and pass it through two different micron cartridge filters before moving the water to the booster pump. Once there, the water reaches around 90 psi before it’s moved once more to an intensifier pump–here, pressure increases to 60,000 psi.

Common Types of Waterjet Machines

Abrasive Waterjet Machines: When using an abrasive waterjet machine, the mechanism of material removal is not the stream itself. Rather, the stream accelerates abrasive particles to erode the material. With that being said, these machines can cut hard materials such as metals, stone, and ceramics. The streams of these machines measure between 0.020 and 0.050 inches in diameter–making them larger than pure waterjet streams. These larger streams make it possible to cut stacks of materials up to 10 inches thick with ease. However, in spite of their increased strength, cutting forces for abrasive streams still measure less than one pound.

Pure Waterjet Machines: These machines are the original waterjet cutters, with a history dating back to the early 1970s. They create less moisture on material, making them suitable for production of products such as automotive interiors and disposable diapers. Their streams are very thin–about 0.004 to 0.010 inches in diameter–and provide extremely detailed geometries and very little material loss.

Cutting Heads for Waterjet Machines

When considering cutting heads for waterjet machines, it’s important to remember that it’s not pressure that tears away pieces or grains of material–instead it’s stream velocity. To achieve a high velocity, pressurized water passes through a hole in a jewel that’s affixed to the end of the nozzle. Sapphires, rubies and diamonds are some of the most common choices.

Each choice however, has different specialties in waterjet cutting. Sapphires are the most common choice for both methods of waterjet cutting and last for approximately 50 to 100 cutting hours. Rubies on the other hand are unsuitable for Pure Waterjet Cutting, but are excellent for abrasive cutting. During abrasive cutting, rubies last about 50 to 100 cutting hours. Diamonds are more expensive than sapphires and rubies, but are far more durable when it comes to usage. In some circumstances diamond orifices can be ultrasonically cleaned and reused. Outside of those circumstances, diamonds typically last between 800 and 2,000 cutting hours.

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