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 as wood, coal, textiles, rocks, concrete, asbestos.
• The mechanism of material removal rate is by erosion. When a high-pressure water jet emerges from a nozzle, it attains considerable kinetic energy.
• A 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.

Characteristics of Water Jet Machining:

• The pressures generally used in WJM are 1500 to 4000 MPa.
• The nozzle is made of sintered diamond and the exit nozzle is about 0.05 to 0.35 mm in diameter.
• There are no moving parts in the system, so there are fewer operating and maintenance costs and a 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 of Water Jet Machining:

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

In AWJM, abrasives below 0.45-micron size are 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 cutting rate is 35.5 mm/min, but on the same work, Electric Discharge Machining (EDM) can cut 2.5 mm/min.