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Abrasive Jet Machining (AJM) Case Studies. Some Studies on Abrasive Jet Machining Authors P.K. Ray and Dr. A.K. Paul Department of Mechanical Engineering Regional Engineering College Rourkela Journal of the Institution of Engineers (India) Volume 68, 1987. Introduction. - PowerPoint PPT Presentation
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Abrasive Jet Machining (AJM)
Case Studies
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Some Studies on Abrasive Jet Machining
Authors
P.K. Ray and Dr. A.K. PaulDepartment of Mechanical Engineering
Regional Engineering CollegeRourkela
Journal of the Institution of Engineers (India)Volume 68, 1987
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An AJM setup may be of two types:
(i) Using a vortex type mixing chamber – abrasive particles are
carried by the vortex motion of the carrier gas.
(ii) Using a vibratory mixing chamber – abrasive particles are
forced into the path of carrier gas by vibratory motion.
The erosion phenomenon may be considered as two phases.
(i) Transportation problem - flow rate, direction and velocity of the
impinging particles.
(ii) Problem of determining material removal rate or erosion rate.
Introduction
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Erosion is a function of
(i) Speed and angle of impact
(ii) Ductility and/or brittleness of material as well the particles
(iii) Elasticity of the material
(iv) Shape and geometry of impinging particles
(v) Impinging particle diameter to material thickness ratio
(vi) Average flow stress
(vii) Materials density
(viii)Stand-off distance.
Introduction
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According to Finnie (1960), MRR
Where, M & V - Mass flow rate and velocity of abrasives
- Angle of impingement
C, n - Constants
- Minimum flow stress of
the materials
Sheldon & Finnie (1966) optimized ‘’ for max MRR. (For brittle - 90
and for ductile – 20 - 30)
Pandey (1977) and Bhatacharya (1976) studied the effect of
abrasive flow rate (AFR) and stand-off distance (SOD) on MRR.
Authors - studied the effect of gas pressure on MRR, AFR and
MRF (Material Removal Factor) during experimentation on an
indigenous AJM setup developed in their lab.
Literature
nMVCf )(
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AJM Nomenclature
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Experimental Setup
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Nozzle & Mixing Chamber
SS Nozzle life – 2 hrNozzle dia - 1.83 & 1.63 mm
Abrasives – SiC (60 & 120 µm)Workpiece – porcelainProcess – hole drilling
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Effect of Pressure on MRR
MRR increases with pressure.
There is a threshold pressure
below MRR is negligible.
MRR increases with increase in
nozzle diameter, grain size and
SOD.
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Effect of SOD on MRR
They also stated as found by other
researchers that MRR increases
initially and remains constant for a
small range.
Then it falls with further increase in
SOD.
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Effect of Pressure on AFR
It is found that AFR is proportional to the pressure.
As pressure increases, AFR increases.
Also, higher the grain size of abrasive particles, AFR is
higher for the given pressure.
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Effect of Pressure on MRF
MRF = MRR / AFR
MRF decreases with increase in pressure.
Quantity of material removed per gram of
abrasive at a higher pressure is less than that
at a lower pressure.
At higher pressure, AFR is higher – meaning
more number of abrasive particles.
This reduces gas flow rate and affects the
removal of debris (tiny particles from work).
Higher AFR – inter particle collision – loss of
energy.
Cushioning effect of trapped abrasive
particles.
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Conclusion
AJM with SiC – suitable for hard and brittle materials like porcelain.
Use of SS nozzle is justified by its low cost, though it has a very low
life.
Nozzle changeover time – less than half a minute.
MRF – maximum for the pressure range of 2 – 3 kgf/cm2
Increase in MRF beyond 4 kgf/cm2 pressure is marginal.
MRF & MRR – higher for higher SOD.
Thus, higher SOD is preferable where MRR is of prime importance.
In precision work, a higher pressure and a lower SOD may be
adopted for better accuracy and penetration rate.
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