Page 141 - Module DMV20173

7.0 NON CONVENTIONAL PROCESSES

7.5 WATER JET MACHINING

1. Water jet machining (WJM) uses a fine , high-pressure, high-velocity stream of

water directed at the work surface to cause cutting of the workpiece.
2. A variety of materials can be cut using WJM.
3. Example of those materials are plastics, fabrics, rubber, wood products, paper,
leather and composite materials.
4. A water jet machining operation is shown in Figure 7.6.

5. The typical nozzle opening diameter is 0.05 to 1 mm.
6. The water pressure level of 400 MPa is generally used in machining operation.
7. The water jet velocity reaches 900 m/s.
8. The nozzle unit consists of a holder made of stainless steel and a jewel nozzle

made of sapphire, ruby, or diamond.
9. Cutting fluids used in WJM are polymer solutions.
10. Important process parameters include standoff distance, nozzle opening
parameter, water pressure, and cutting feed rate.
11. A smaller standoff distance is desirable in order to minimize dispersionof the fluid

stream.
12. A typical standoff distance is 3.2 mm.
13. Among the advantages of WJM process are:

 No heat is produced.
 No environmental pollution.
 No deflection of the workpiece.
 The burr produced is minimal.

14. A limitation of WJM is that the process is not suitable for cutting brittle materials
because of their tendency to crack during cutting.

7.5.1 ABRASIVE WATER JET MACHINING

1. Abrasive particles are added to the jet stream when cutting metallic, nonmetallic
and advanced composite materials workpiece.
2. This process is known as abrasive water jet machining (AWJM).
3. Typical abrasive particles used are aluminum oxide, silicon dioxide, and garnet.
4. The typical grit size of the particles are between 60 to 120.

5. The nozzle orifice diameers are in the range 0.25 – 0.63 mm which is slightly
larger than in WJM.
6. Standoff distance in AWJM is about ¼ and ½ of those in WJM.

BPLK 173 DMV 20173