Operation, advantages, disadvantages and applications of abrasive jet machining
Construction-
In Abrasive Jet Machining, the gases used are generally air and nitrogen. The abrasives used are aluminum oxide, silicon carbide, glass powder and sodium carbonate. The main size varies from 10 meters to 50.
Smaller sized particles are used to obtain good surface finish and precision, while larger sized particles provide fast material removal rate. The nozzles are made of hard material such as tungsten carbide or ceramic to withstand a high degree of abrasive wear. The abrasive gas mixture, jet pressure, abrasive particle size, and hardness are primarily responsible for the metal removal rate. The metal removal rate for this type of process is generally 16 mm^3/min in glass cutting and the jet speed varies from 150 to 300 meters per minute.
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Abrasive jet machining work
Abrasive jet machining work
When abrasive particles hit the workpiece at high speed, this impact causes a fracture. There are many parameters that influence the material removal rate.
1. Abrasives-
The metal removal rate depends on the composition, strength, size and mass flow rate of the abrasive particles. The material removal rate increases with increasing mixing ratio. A further increase in the mixing ratio decreases the Metal Removal Rate. The mass flow rate of the abrasive particle depends on the gas pressure. The material removal rate increases linearly with increasing mass flow rate.
2. Gas-
Since the velocity pressure depends on the gas composition, the material removal rate is mainly affected by the gas composition.
3. Mouthpiece-
In a nozzle, abrasive grains flow continuously at a very high speed. Thus, the nozzle is the most important element for controlling the process characteristics. The important parameter is the distance between the work surface and the nozzle tip, known as nozzle tip distance. When the distance from the nozzle tip increases, the speed of abrasive particles colliding with the workpiece also increases. The increase in abrasive speed not only affects the rate of metal removal, but also the shape and size of the hole or cavity produced in the workpiece. The metal removal rate increases with increasing distance from the nozzle tip up to a maximum value. Further increase in distance from the nozzle tip decreases the rate of metal removal as the velocity will be reduced due to drag from the atmosphere.
Advantages of abrasive jet machining-
1. This method makes it easy to machine complex holes and intricate cavities from harder materials into the desired shape.
2. Brittle metals which are very difficult to machine in conventional machining process are easily machined by this process with better precision.
3. Machining can be carried out easily for thin section brittle materials.
4. Capital investment is very low.
5. There is no direct contact between the workpiece and the tool.
6. The heat generated in this process is very less.
Disadvantages of abrasive jet machining
1. The material removal rate is very slow.
2. This process is not applicable for ductile materials.
3. Low machining precision.
4. Abrasive dust cannot be recycled or recovered.
5. Cleaning the work material is necessary after operation, as there is a danger of abrasive particles adhering to the material.
Abrasive jet machining applications-
1. This method is used in microwelding, fine drilling and aperture drilling for electron microscope.
2. Used in machining complex profiles in brittle and hard metals.
3. Used for semiconductor machining.
4. This method is also employed to perform cleaning and cutting operations on materials such as silicon, germanium, quartz, mica and many more.
5. Abrasion and freezing of fragile materials such as glass, ceramics, refractories and many more.
