Water jet cutting is a subtractive manufacturing process that uses a narrow, high-pressure stream of water to cut material along a computer-controlled path. For harder materials such as metal, stone, and engineering plastics, an abrasive—typically garnet—is mixed into the stream to increase its cutting power; pure water jets are used for softer materials. The jet removes material by erosion, producing a narrow cut known as a kerf. Because the process does not rely on heat, it avoids the heat-affected zone associated with thermal cutting methods. Cut quality and accuracy depend on factors such as water pressure, abrasive flow, nozzle condition, material thickness, and cutting speed.

Water jet cutting is a good choice when a custom plastic component is cut from sheet or plate, especially if the material is thick or sensitive to heat. It follows a programmed outline without needing a mould, so it works well for prototypes and small batches. Because the cut is cold, it avoids melting or heat distortion at the edge; it can also cut reinforced plastics without the tool-clogging problems of conventional machining.

It is best suited to profile cutting—for example, custom panels, gaskets, or blanks. If the part needs pockets, threads, or precise three-dimensional features, it will generally need a further machining step.

Water jet cutting is usually used for components whose shape can be cut from a flat sheet or plate, such as:

• Custom panels, covers, and machine guards
• Gaskets, seals, and foam inserts
• Spacers, washers, and mounting plates
• Liners and wear pads
• Blanks for composite brackets or other parts that will be finished by machining

For plastic components, it is especially useful when the material is thick, reinforced, or sensitive to heat. The result is mainly a cut outline with through-holes; features such as pockets and threads need another process.