The machining process in which a water jet is used to remove material from the workpiece is called Water jet machining(WJM).
In this process, a water jet is used which acts as a tool in the form of water saw.
In this process water is greatly accelerated and further concentrated on the target workpiece.
This water jet at a high velocity and pressure is able to slice material and some metals using some abrasive particles mixed in it.
In some processes, no abrasives are used and these processes are known as pure water jet machining processes.
The water pressure used in this machining process is from 200 MPa to 400 MPa. The pressure is varied according to the workpiece whose material is to be removed.
This process resembles the water erosion phenomenon existing in nature.
It is mainly used to remove material from soft and non-metallic workpieces like plastic, rubber, glass, etc.
A high velocity water jet is used in this process to remove material from the workpiece.
The basic principle of this process is that the Kinetic energy of the water jet should be changed into pressure energy so that it removes material from the workpiece.
When water jet with kinetic energy collides with a workpiece then this kinetic energy will be changed into pressure energy.
This pressure energy will induce stress to the workpiece and due to this stress material will start removing from the workpiece.
Parts of Water Jet MachiningProcess:
The reservoir is used to store water which will be used as a jet. From the reservoir, the water is supplied for the water jet machining process.
This pump will suck water from the reservoir and it will transfer the water to the intensifier. The pump is used to create pressure in the water from 1500 to 4000 bars. For achieving this pressure,50 to 100 HP electric motor is used.
The intensifier is used to increase the water jet pressure and produces high pressure liquid jet. This intensifier is connected to the accumulator. It accepts the water at low pressure and expels it through an accumulator at high pressure. It works through a hydraulic reciprocating mechanism.
The accumulator is used to temporarily store the water according to requirements. This accumulator is connected to the control valve. It maintains the continuous flow of high pressure water and eliminates pressure fluctuation.
5) Control Valve:
This control valve controls the pressure of water as well as the quantity of water to be pass and directs it towards the flow regulator. This is where the pressure energy will be changed into kinetic energy.
6) Flow Regulator:
The flow of water that reaches from control valve is regulated using the flow regulator. After regulating the flow regulator pass the water to the nozzle i.e high pressure of water will change into high velocity water.
This nozzle will covert the pressure of high pressure jet into kinetic energy. The kinetic energy is increased because the area reduces at the end of the nozzle. After that the water jet from the nozzle is directed towards the workpiece.
The water which is directed from the nozzle will come out from this orifice.
9) High Presure Tubes:
High Pressure Tubes are required for the flow of high pressure water. They are nearly 6 to 14 mm in diameter. It also allows flexible movement of the cutting head.
10) Catcher or drain:
The catcher or drain is used to collect the water after it cuts the workpiece. From here the water is sent for further purification or may be recirculated.
Working of Water Jet Machining:
- At first, the water is transferred to the intensifier using a pump.
- The intensifier accepts the water at low pressure and then transfer it to the accumulator at high pressure of nearly 3800 bar.
- The accumulator temporarily stores the high pressure water.
- From the accumulator the high pressure water is transferred to the control valve which controls the direction of the water. In the control valve, the pressure energy of water is changed into kinetic energy i.e high pressure water changes to high velocity water and this high velocity water is sent to flow regulator.
- Flow regulator regulates and controls the flow rate of water and directs it toward the nozzle.
- In the nozzle, the kinetic energy of water is increased tremendously and high velocity water is produced from the nozzle. Then the water comes out from the orifice and is directed towards the workpiece.
- When the water jet reaches the workpiece, the Kinetic Energy again changes into pressure energy and whole pressure will be applied to the workpiece. This pressure due to water jet will cause some fractures in part of the workpiece where water jet stikes and some cracks will be initiated in the workpiece surface and as the water jet continuously strikes the workpiece surface for a longer period, the initiated crack will get deepen and therefore material will be removed from the workpiece.
- The material which is removed is carried away by the water along with it.
- After the material is removed the water which cuts the material is collected for further use. This water will contain some parts of the chips of the material which is cut using this process.
- This water will be sent for further purification or may be recirculated through the whole process of water jet machining.
1) Unlike other metal cutting methods, this method does not generate high heat affected zones (HAZ). Heat affected zone is present near the cutting zone.
2) This process is free from fabrication induced defects.
3) This process is also environment friendly.
4) The cut edges produced using this process are clean because there is no heat involved.
5) The weldability of material is not reduced in this process.
1) Some water mist may be created in the environment which can cause some harm to sensitive equipments.
2) It will be not easy to cut very thick material using this process.
3) The initial cost is high.
1) It is used in the fabrication.
2) It is also used in the manufacturing of machinery parts.
3) It is used in the mining industry where rocks and hard materials are cut easily without causing any chemical disturbance to mild materials.
4) It is also used in aerospace industries for cutting, shaping, carving, etc.