ABRASIVE JET MACHINING
Abrasive jet machining is mechanical energy based unconventional machining process used to remove unwanted material from a given work piece.
|ABRASIVE JET MACHINING|
CONSTRUCTION OF ABRASIVE JET MACHINING:
It consist of Compressor ( To pressurize the gas ), Filter, mixing chamber, Hopper, Vibrator, Nozzle, Pressure gauge and flow regulator.
The nozzle is made of a hard material like tungsten carbide.
Abrasive used are aluminum oxide, Silicon carbide, or Sodium bicarbonate.
The gases commonly used are air, N2, CO2.
Hopper is placed above mixing chamber for feeding purpose.
Vibrating device placed below mixing chamber to vibrate mixture of abrasive and gas.
In Abrasive Jet Machining (AJM), abrasive particles are made to impinge on the work material at a high velocity.
The high velocity abrasive particles remove the material by micro- cutting action as well as brittle fracture of the work material.
In AJM, generally, the abrasive particles of around 50 μm grit size would impinge on the work material at velocity of 200 m/s from a nozzle of I.D. of 0.5 mm with a standoff distance of around 2 mm.
The kinetic energy of the abrasive particles would be sufficient to provide material removal due to brittle fracture of the work piece or even micro cutting by the abrasives.
WORKING ABRASIVE JET MACHINING
First dry air or gas is filtered and then it compressed by compressor.
A pressure gauge and flow regulator control the pressure and regulate the flow of the compressed air. Compressed air entered into the mixing chamber where it mixed with abrasive particles.
Then mixture passes through nozzle where high velocity fine abrasive jet is produced. The nozzle increases velocity about 200 to 400 m/s at the expense of it’s pressure.
Process Parameters and Machining Characteristics
APPLICATIONS OF ABRASIVE JET MACHINING
1. Drilling, Cleaning, and polishing of hard surface.
2. To machine intricate shapes which is difficult to machine.
3. Aircraft fuel system, Medical appliances and Hydraulic valves.
Advantage of Abrasive Jet Machining:
1. No heat is generated in work. So it is suitable for heat sensitive materials.
2. No physical contact between tool and work.
3. Thin and fragile materials also machined.
4. Low investment.
5. Smooth surface finish.
Disadvantage of Abrasive of Jet Machining
1. Low MRR.
2. Abrasive powder cannot be reused.
3. Nozzle life is less and maintenance of nozzle required.
Factors affecting performance of AJM:
1. Abrasive grain size and It’s mass flow rate
2. Mixing ratio.
3. Velocity of abrasive particles.
4. Gas pressure.
5. Nozzle tip distance.
Modeling of material removal
Material removal in AJM takes place due to brittle fracture of the work material due to impact of high velocity abrasive particles.
Modeling has been done with the following assumptions:
(i) Abrasives are spherical in shape and rigid. The particles are characterized by the mean grit diameter
(ii) The kinetic energy of the abrasives are fully utilized in removing material
(iii) Brittle materials are considered to fail due to brittle fracture and the fracture volume is considered to be hemispherical with diameter equal to choral length of the indentation
(iv) For ductile material, removal volume is assumed to be equal to the indentation volume due to particulate impact