Water jet machines cut with a hair-thin stream of water moving at very high speed. They’re used for cutting soft materials where the low cutting forces minimize deflection and those with low melting points but can also cut ceramics, stone, glass, and steel.

Machine Structure and Components

A CNC water jet machine looks similar to a CNC laser or plasma cutter. The cutting head is on a gantry that moves over a table holding the sheet-form workpiece. The CNC system coordinates X and Y axis motion to enable the cutting of complex contours.

The other key element is the water delivery system. This comprises a pump and a cutting head. The pump delivers water at high pressure, (up to 90,000 psi), to the cutting head. Here it passes through an orifice some 0.010” in diameter which accelerates it to supersonic speeds. As a general rule, the higher the jet velocity the faster the machine can cut.

Five other things you should know are:

1. Add abrasive to cut hard material

Water jets can cut soft material like automotive interior panels and headliners quickly. Cutting hard materials requires the addition of an abrasive, usually garnet, to the water stream. Grit size influences cutting speed and edge quality.

2. Water jet consumables need frequent replacement

While garnet can be recovered and recycled, for costing purposes it should be considered consumable. Other notable consumables include:

  • The jewel that forms the orifice in the cutting head – rubies last up to 100 hours, diamonds up to 2,000
  • The mixing tube inside the cutting head – brittle and easily damaged, typical life is 150 hours
  • Water filters – clean water is essential for process consistency so filters must be replaced frequently

3. Two types of pump

It takes a special kind of pump to create the pressures needed in a water jet machine. Machines with up to 50,000 psi typically use a direct drive pump, similar to those found in power washers. The really high-power machines use a reciprocating pump where the output is coupled to a shock attenuator that smooths out the pulses.

4. Available in a wide range of sizes

CNC water jet machines are available in sizes to meet every need and shop. The smallest have a bed of 2’ x 3’ while the largest are 30’ x 100’. Most shops will probably find a bed around 6’ x 8’ that optimizes output and productivity.

5. Create high-quality edges

Edge quality is related to grit size, but smooth edges are achieved even with coarse grit. Unlike laser or plasma cutting, there’s no heat-affected zone because the water cuts without heat. In addition, the kerf is usually less than 0.050”, which can improve material utilization.

Accuracy diminishes with increase cut depth. On materials less than 1” thick it’s usually possible to maintain tolerances better than 0.005”. Accuracy falls slightly on thicker materials as the jet has more opportunity to deviate.

2D Cutting Capabilities

A CNC water jet machine can be a valuable addition to any shop that cuts 2D profiles from sheet or plate. Water jet cutting is especially effective for both very soft materials and hard non-metallics like ceramics and composites. If you’re looking to add a water jet machine to your operation, The Equipment Hub can help.

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