- 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 of a nozzle, it attains a large kinetic energy.
- High velocity jet strikes the work piece, 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 of Water Jet Machining (WJM):
- The pressures normally used in WJM are 1500 to 4000 MPa.
- Nozzle is made by sintered diamond and exit nozzle is about 0.05 to 0.35 mm.
- 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 of Water Jet Machining:
- Initial setup cost for Water Jet Machining process is very high and hard materials cannot be cut.
- Cutting of hard materials have been over come 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 Al has been cut for 100 mm/min.
On zinc-nickel steel of 25mm thick the rate of cutting is 35.5 mm/min, but on the same work EDM can cut 2.5 mm/min.