The document summarizes abrasive jet machining (AJM), an unconventional machining process. In AJM, a high velocity jet of abrasive particles carried by compressed air or gas is directed at a workpiece to remove material. Key aspects of AJM include the gas propulsion system, abrasive feeder, machining chamber, AJM nozzle, and abrasives used. AJM is useful for machining brittle materials and provides better surface finish than conventional machining. The document outlines the various components and process of AJM.

1. DRAFT REPORT
ABRASIVE JET MACHINING
ADARSH S
LADR19ME091
S7 ME A

2. ABSTRACT
Abrasive Jet Machining is an unconventional machining
method in which, a jet of high velocity air-abrasive particles is
directed onto a work piece to remove material from it. The
AJM process is especially useful in machining brittle materials
and is seldom employed for machining ductile materials. Early
researches in the field had mostly been experimental
investigations. The few attempts to theorize the mechanics of
material removal used very crude models. The present
research work is aimed mainly at proposing a suitable theory,
which explains the mechanics of AJM. To do this the
established theories of elasticity and fluid flow have been
employed. It is widely recognized that the impact of abrasive
particles and the consequent transfer of energy to the work
medium is the cause for material removal. The impact is
modelled as an impulse resulting in transient stress and strain
field in the medium. The standard equations of elasticity
theory (Navier's formulation) are solved to determine the
stress and strain field. For ascertaining fracture, a criterion
based on strain energy density is employed and a material
property (SED) is introduced. The process parameters are
introduced at this stage, through the analysis of the air-
abrasive flow. The governing equations for the flow are the
adaptations of the Navier - Stokes equations for the fluid and
equations of motion for the particles

3. INTRODUCTION
Abrasives are costly but the abrasive jet machining
requires very less investment and less maintenance
cost. The carrier gas is used as coolant, the cutting
action is accurate and therefore better surface finish is
obtained. In the current day situation it is widely used in
manufacturing of electronic devices such as LCD's, PCB,
MEMS, and semiconductors. There is increase in
demand for development of micromachining
technologies for materials which are difficult-to-
machine because of their properties such as extreme
hardness, brittleness, corrosion resistance and low
melting temperatures. AJM is used to carry out
operations like cutting, cleaning, polishing, de burring,
etching, drilling and finishing the operation. The nozzle
is the most important part in the abrasive jet
apparatus/setup. The process is mainly used to cut
difficult and deep shapes in hard and brittle materials
which are sensitive to heat. The process can be easily
controlled by varying the parameters such as Velocity,
Flow rate, Pressure, Standoff distance, Grit size, and
nozzle angle. Abrasive jet machining (AJM) is a non-
traditional machining process which operates
workpiece without producing heat and shock.

4. Abrasive Jet Machining
 In Abrasive Jet Machining (AJM), abrasive particles
are made to impinge on the work material at a
high velocity. The jet of abrasive particles is
carried by carrier gas or air.
 High velocity stream of abrasive is generated by
converting the pressure energy of the carrier gas
or air to its kinetic energy and hence high velocity
jet.
 Nozzle directs the abrasive jet in a controlled
manner onto the work material, so that the
distance between the nozzle and the work piece
and the impingement angle can be set desirably.
 High velocity abrasive particles remove the
material by micro-cutting action as well as brittle
fracture of the work material.

5. Process :-
 In AJM, air is compressed in an air
compressor and compressed air at a pressure
of around 5 bar is used as the carrier gas.
 Gases like CO2 , N2 can also use. Generally
oxygen is not used as a carrier gas.
 Carrier gas is first passed through a pressure
regulator to obtain the desired working
pressure. Gas is then passed through an air
dryer to remove any residual water vapour.
To remove any oil vapour or particulate
contaminant the same is passed through a
series of filters.
 Then the carrier gas enters a closed chamber
known as the mixing chamber.
 Abrasive particles enter the chamber from a
hopper through a metallic sieve.
 Sieve is constantly vibrated by an
electromagnetic shaker.

6. Abrasive jet Machining consists of
1. Gas propulsion system
2. Abrasive feeder
3. Machining Chamber
4. AJM Nozzle
5. Abrasives

7. Gas Propulsion System
 Supplies clean and dry air.
 Air, Nitrogen and carbon dioxide to propel the
abrasive particles.
 Gas may be supplied either from a compressor
or a cylinder.
 In case of a compressor, air filter cum drier
should be used to avoid water or oil
contamination of abrasive powder.
 Gas should be non-toxic, cheap, easily
available.
 It should not excessively spread when
discharged from nozzle into atmosphere.
 Propellant consumption is of order of 0.008 m3
/min at a nozzle pressure of 5 bar and abrasive
flow rate varies from 2 to 4 gm/min for fine
machining and 10 to 20 gm/min for cutting
operation.

8. Abrasive Feeder
 Required quantity of abrasive particles is supplied
by abrasive feeder. Filleted propellant is fed into
the mixing chamber where in abrasive particles are
fed through a sieve.
 Sieve is made to vibrate at 50-60 Hz and mixing
ratio is controlled by the amplitude of vibration of
sieve.
 Particles are propelled by carrier gas to a mixing
chamber. Air abrasive mixture moves further to
nozzle.
 Nozzle imparts high velocity to mixture which is
directed at work piece surface.
Machining chamber
 It is well closed so that concentration of
abrasive particles around the working
chamber does not reach to the harmful
limits.
 Machining chamber is equipped with vacuum
dust collector.
 Special consideration should be given to dust
collection system if the toxic material (like
beryllium) are being machined.

9. AJM nozzle
 AJM nozzle is usually made of tungsten
carbide or sapphire (usually life – 300 hours
for sapphire , 20 to 30 hours for WC) which
has resistance to wear.
 Nozzle is made of either circular or
rectangular cross section and head can be
head can be straight, or at a right angle.
 It is so designed that loss of pressure due to
the bends, friction etc is minimum possible.
 With increase in wear of a nozzle, the
divergence of jet stream increases resulting
in more stray cutting and high inaccuracy.
Abrasives
 Material – Al2O3 SiC Glass beads Crushed
glass Sodium bi carbonate
 Shape – irregular/regular
 Size – 10 to 50 microns
 Mass flow – 2-20 gm/min

10. Applications
•Paintremoval
•Cutting soft materials
•Cutting frozen meat
•Textile
 Leatherindustry
•MassImmunization
•Surgery
•Peening
•Cutting
•Pocket Milling
•Drilling

11. Conclusion
 The better performance, and the applications
represented above statements confirm that
 ABRASIVE JET MACHINING is continue to expand.
 The new software's used to minimize time and
investments, there by making it possible for
more manufacturers of precision parts to install
AJM centers .
References
 Texas Airsonics, archived from the orginal on
March 4, 2012.
 Boothroyd, Geoffrey; Knight, Winston (1989),
Marcel Dekker, pp. 478–9,
 Todd, Robert H.; Allen, Dell K.; Alting, Leo
(1994),, Industrial Press Inc., pp. 2–5,
 Chastagner, Matthew W.; Shih, Albert J.
(2007), Transactions of NAMRI/SME, 35:359–366.