A brief explanation about Abrasive Jet Machining.

1. INTRODUCTION TO ABRASIVE
JET MACHINING (AJM)
DEPARTMENT OF MECHANICAL ENGINEERING
Course Coordinator: Anjan Kumar.D
Assistant Professor
Team Members:
Sheik Irfan : 1AT18ME041
Shishir.U.Shinde : 1AT18ME042
Shivaram.M : 1AT18ME043
Shyam Sunder Reddy : 1AT18ME044
Sudeep.S : 1AT18ME045
ATRIA INSTITUTE OF TECHNOLOGY

2. Content in Presentation
● Introduction to AJM
● Need for AJM
● Machining Principle
● Equipments
● Process Parameters
● Characteristics of AJM
● Advantages
● Disadvantages
● Applications
● Youtube Links

3. Introduction to Abrasive Jet Machining
● AJM is the process of impinging the high speed stream of abrasive particles like silicon
carbide by high pressure gas or air on work surface through nozzle and removal occurs due
to erosion.
● The water jet contains abrasive particles such as silicon carbide or aluminium oxide in
order to increase the material removal rate.
● Almost any type of material ranging from hard brittle materials such as ceramics, metals
and glass to extremely soft materials such as foam and rubbers can be cut by abrasive water
jet cutting.
● The narrow cutting stream and computer controlled movement enables this process to
produce parts accurately and efficiently.
● This machining process is especially ideal for cutting materials that cannot be cut by laser
or thermal cut.
● Metallic, non-metallic and advanced composite materials of various thicknesses can be cut
by this process.
● This process is particularly suitable for heat sensitive materials that cannot be machined by
processes that produce heat while machining.

4. Need for AJM
● Intricate shapes in hard & brittle materials, which are sensitive to heat, inaccessible by
ordinary machining methods, or having a tendency to chip easily can be machined
efficiently using AJM.
● This makes the process to be selected for machining.
● The fundamental principle of AJM involves the use of a high-speed stream of abrasive
particles carried by a high-pressure gas or air on the work surface through a nozzle.
● The metal is removed due to erosion caused by the abrasive particles impacting the work
surface at high speed.

5. Machining Principle

6. Machining Principle
● 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.
● The 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.
● The nozzle directs the abrasive jet in a controlled manner onto the work material, so that
the distance between the nozzle and the workpiece and the impingement angle can be set
desirably.
● The high velocity abrasive particles remove the material by micro-cutting action as well as
brittle fracture of the work material.
● 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 be used as carrier gas which may directly be issued from a gas
cylinder.
● Generally oxygen is not used as a carrier gas.

7. ● The carrier gas is first passed through a pressure regulator to obtain the desired working
pressure.
● 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.
● The abrasive particles enter the chamber from a hopper through a metallic sieve. The sieve
is constantly vibrated by an electromagnetic shaker.
● The mass flow rate of abrasive (15gm/min) entering the chamber depends on the amplitude
of vibration of the sieve and its frequency.
● The abrasive particles are then carried by the carrier gas to the machining chamber via an
electromagnetic on-off valve.
● The machining enclosure is essential to contain the abrasive and machined particles in a
safe and eco friendly manner.
● The machining is carried out as high velocity (200 m/s) abrasive particles are issued from
the nozzle onto a workpiece traversing under the jet.

8. Equipments of AJM
1. Nozzle
● In 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.
● The nozzle directs the abrasive jet in a
controlled manner onto the work material,
so that the distance between the nozzle
and the workpiece and the impingement
angle can be set desirably.
● The high velocity abrasive particles remove
the material by micro-cutting action as
well as brittle fracture of the work
material.

9. 2. Abrasives
● Aluminium Oxide
● Silicon Carbide – Preferred only when the w/p is very hard.
● Sizes : 10-20µm.
● Smaller Size : Cleaning, Polishing.
● Larger Size : Cutting & peening operations.
● Should remain suspended in the carrier gas.
● Should have excellent flow characteristics.
● Air – must be filtered.
● Nitrogen
● Carbon Dioxide
● Pressure required : 2-8kg/cm².
● High pressure – leads to nozzle wear.
● Low pressure – Low MRR.
3. Carrier Gas

10. 4. Metering System
● It includes mixing chamber, regulator, valves & other devices.
● System must inject a uniform, adjustable flow of abrasives of abrasive
particles into the gas stream.
● Powder Hopper – feeds into the vibrating chamber.
● Chamber turns causes the powder to be metered uniformly into the Jet
stream.
● Amplitude of Vibration of the Mixing chamber controls it.
● Mixing chamber consisting of carrier gas and the abrasive grains, vibrates at
a frequency of 50 Hz

11. Process Parameters
● Abrasive Flow Rate
● Velocity
● NTD (Nozzle Tip Distance) or SOD (Stand-Off Distance)
● Abrasive Grain Size.
● Mean Number of abrasive particles per unit volume of the carrier
gas.
● Nozzle Design.

12. 1. Abrasive Flow Rate
2. Mean number of Abrasive per
unit volume of the carrier gas
● AFR ∝ MRR.
● When exceeds 14g/min, Velocity decreases, thereby reduces MRR.
● Minimum Velocity : 150m/sec.
● Mixing Ratio, M = (Volume flow rate of the abrasive per unit
time)/(Volume flow rate of the carrier gas per unit time)
● Large M – Higher MMR.
● Large abrasive flow rate sometimes may evn clog the nozzle.

13. 3. NTD or SOD
● It refers to the distance between the tip of the nozzle & the workpiece.
● NTD also affects the shape & size of the cavity produced.
● A large NTD results in the flaring up of the Jet, it spreads over a wide area, decreasing its
intensity....leading to poor accuracy.

14. 4. Abrasive Grain Size
● Size : 10-15µm.
● Larger size removes material faster.
● Coarse grains recommended for cutting.
● Fine Grain abrasives for polishing & deburring etc.
A burr is a raised edge or small piece of material that remains attached to a workpiece
after a modification process. It is usually an unwanted piece of material and is removed
with a deburring tool in a process called ‘deburring’.
Deburring

15. 5.Nozzle Design
● Subjected to abrasive wear.
● Wear resistant materials like Tungsten, Sapphire.
● Should be carefully designed so that pressure loss due to bends, friction.. Is minimum.
● It can be either in circular or rectangular in cross section.
● Nozzle Tip : ID 0.18-0.8mm.

16. Process Capabilities or Characteristics of AJM
1. MRR:
● 16mm³/min in cutting glass.
● A minimum width of about 0.1mm can be cut using a rectangular nozzle with an orifice of
0.075x1.5mm placed at a distance of 0.08mm from the workpiece

17. 2. Accuracy:
● Under optimum machining conditions, a tolerance in the region of ±0.05mm can be
obtained.
● Under normal production work, the tolerance value exceeds to 0.1mm.
3. Surface Finish: 0.4-1.2µm.
4. Corner Radius: Limited to 0.1mm.
5. Taper: 0.05mm per 10mm penetration. (metal removal)

18. Advantages of AJM
● High surface finish can be obtained depending upon the grain sizes.
● Depth of damage is low (around 2.5 microns).
● It provides cool cutting action, so it can machine delicate and heat sensitive material.
● Process is free from chatter and vibration as there is no contact between the tool and
workpiece.
● Capital cost is low and it is easy to operate and maintain AJM.
● Thin sections of hard brittle materials like Germanium, Mica, Silicon, Glass and
Ceramics can be machined.
● It has the capability of cutting holes of intricate shape in hard materials.

19. Disadvantages of AJM
● Abrasives cannot be reused.
● Short NTD when used for cutting may damage to nozzle tip.
● The major disadvantages of abrasive jet is high noise levels during operation.
● Resilient materials such as rubber & some plastics cannot be processed by AJM.
● MRR is Low.
● High impinging velocity of the abrasives results in embedding in the workpiece.

20. Applications of AJM
● AJM is useful in manufacture of electronic devices, drilling of glass wafers, deburring of
plastics, making of Nylon and Teflon parts permanent marking on rubber stencils, cutting
titanium foils.
● Used for cutting thin fragile components like Germanium, Silicon, etc.
● Used for Cleaning of metallic smears on ceramics, oxides on metals, resistive coating,etc.
● Deflashing small castings, engraving registration numbers on toughened glass used for car
windows.
● Used for Brittle & heat sensitive materials like Glass, Quartz, semiconductor materials,
mica etc.
● Used in drilling holes, cutting slots, deburring, trimming & removing oxides & other
surface films on the workpiece.
● Used in Laboratories to prepare surfaces for strain gauge applications, and to create
artificial flaws in materials for calibration & testing equipments.
● Removing glue & paint from paintings & leather objects.

21. Reference Links
● https://youtu.be/6ERbGtJFcBw
● https://youtu.be/6tXUzECrxjI
● https://youtu.be/dmHv42wda9k
● https://youtu.be/EqpdPc7urGQ
● https://youtu.be/JlHKJpS9ZPo