Mumbai University > Mechanical Engineering > Sem 5 > Production process 3

Marks: 5 M, 6 M

Year: Dec 2014, May 2015

• Water Jet Machining (WJM) is a mechanical energy based non-traditional machining process used to cut and machine soft and non-metallic materials.
• It involves the use of high velocity water jet to smoothly cut a soft workpiece. It is similar to Abrasive Jet Machining (AJM).
• In water jet machining, high velocity water jet is allowed to strike a given workpiece. During this process, its kinetic energy is converted to pressure energy. This induces a stress on the workpiece. When this induced stress is high enough, unwanted particles of the workpiece are automatically removed.

Construction of Water Jet Machining (WJM):

The apparatus of water jet machining consists of the following components:

• Reservoir: It is used for storing water that is to be used in the machining operation.
• Pump: It pumps the water from the reservoir.
• Intensifier: It is connected to the pump. It pressurizes the water acquired from the pump to adesired level.
• Accumulator: It is used for temporarily storing the pressurized water. It is connected to the flow regulator through a control valve.
• Control Valve: It controls the direction and pressure of pressurized water that is to - Flow regulator: It is used to regulate the flow of water.
• Nozzle: It renders the pressurized water as a water jet at high velocity.

Working of Water Jet Machining (WJM):

• Water from the reservoir is pumped to the intensifier using a hydraulic pump.
• The intensifier increases the pressure of the water to the required level. Usually, the water is pressurized to 200 to 400 MPa.
• Pressurized water is then sent to the accumulator. The accumulator temporarily stores the pressurized water.
• Pressurized water then enters the nozzle by passing through the control valve and flow regulator.
• Control valve controls the direction of water and limits the pressure of water under permissible limits.
• Flow regulator regulates and controls the flow rate of water.
• Pressurized water finally enters the nozzle. Here, it expands with a tremendous increase in its kinetic energy. High velocity water jet is produced by the nozzle.
• When this water jet strikes the workpiece, stresses are induced. These stresses are used to remove material from the workpiece.
• The water used in water jet machining may or may not be used with stabilizers. Stabilizers are substances that improve the quality of water jet by preventing its fragmentation.
• For a good understanding of water jet machining, refer the schematic diagram above.

Advantages of Water Jet Machining (WJM):

• Water jet machining is a relatively fast process.
• It prevents the formation of heat affected zones on the workpiece.
• It automatically cleans the surface of the workpiece.
• WJM has excellent precision. Tolerances of the order of ±0.005″ can be obtained.
• It does not produce any hazardous gas.
• It is eco-friendly.

Disadvantages of Water Jet Machining:

• Only soft materials can be machined.
• Very thick materials cannot be easily machined.
• Initial investment is high.

Applications of Water Jet Machining:

• Water jet machining is used to cut thin non-metallic sheets.
• It is used to cut rubber, wood, ceramics and many other soft materials.
• It is used for machining circuit boards.
• It is used in food industry.