Water Jet Machining (WJM)

In Water Jet Machining (WJM) process, water jets alone (without abrasives) can be used for cutting. Thin jets of high pressure and high velocity have been used to cut materials such wood, coal, textiles, rocks, concrete, asbestos.
The mechanism of material removal rate is by erosion. When high-pressure water jet emerges from a nozzle, it attains a large kinetic energy.
High-velocity jet strikes the workpiece, its kinetic energy is converted into pressure energy including high stresses in the work material.
When the induced stress exceeds the ultimate shear stress of the material, rupture takes place.

Schematic illustration of water jet machining

Characteristics:

The pressures normally used in WJM are 1500 to 4000 MPa.
The nozzle is made of sintered diamond and exit nozzle is about 0.05 to 0.35 mm in diameter.
No moving parts in the system, so less operating and maintenance costs and safe process.
No thermal damage to work and intricate shapes can be cut.
The process is convenient for cutting soft and rubber-like materials because teeth will get clogged in conventional methods.

Limitations:

Initial setup cost for WJM process is very high and hard materials cannot be cut.
Cutting of hard materials have been overcome by introducing abrasives in water in WJM also called Abrasive Water Jet Machining (AWJM).

In AWJM abrasives below 0.45-micron size is mixed with water and compressed to 420 MPa with this machine a 25 mm thick Aluminium has been cut for 100 mm/min.

On zinc-nickel steel of 25 mm thick the rate of cutting is 35.5 mm/min, but on the same work, Electric Discharge Machining (EDM) can cut 2.5 mm/min.

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