Abrasive Jet Machining(AJM) is a Non-conventional machining process, Where a nozzle is used to remove the metal from the surface.
Here, you are going to get a complete guide of the AJM machining process, From stretch to the end.
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Abrasive Jet Machining Definition-
Abrasive jet machining(AJM) uses a stream of fine grained abrasive mixed with air or some other carrier gas at high pressure directed by nozzle on the work surface, where metal removal occurs due to erosion caused by the abrasive particle impacting the work surface at the high speed.
In abrasive jet machining, the material is removed by the erosive action of a high-velocity stream of fine abrasive particles transmit on the work surface.
This is the main principle behind the AJM machining process and this process lies in its ability to machine brittle materials with thin sections, especially in areas that are inaccessible by ordinary methods.
Fig.- Schematic diagram of Abrasive Jet machining
Parts and construction-
Here are several parts and construction of the Abrasive Jet Machining-
- Air compressor
- Air Filter
- Pressure Gauge
- Flow Regulator Valve
- Mixing Chamber
(I) Air compressor-
An Air compressor is used to draw air and pressurize it at High pressure.
(II) Air Filter-
The function of the air filter is to clean the impurities present in the atmospheric air.
(III) Pressure gauge-
The pressure gauge is used to show the exact air pressure coming from the air compressor.
(IV) Flow regulator Valve-
The work of the flow regulator valve is to regulate the flow rate of the abrasive jet.
(V) Mixing Chamber-
The mixing chamber is used to mix the compressed air as well as abrasive particles.
Hoper is generally used to feed the abrasive particles into the mixing chamber.
The vibrator presents below the mixing chambers that control the abrasive powder feed rate into the mixing chamber.
The nozzle basically increases the velocity of the mixer.
After knowing the various parts of AJM, I would like to head you towards the Working principle of the AJM machining process.
Working principle of Abrasive Jet Machining-
Step by Step guide of abrasive jet machining working-
- Firstly, Air is drawn to the air compressor, where the air is pressurized in between 25-130psig.
- After the compressor, pressurized air goes to the filter, Where the air is filtered from any atmospheric impurities in the air.
- Now, Pressure is monitored with the help of a Pressure gauge and the next Abrasive jet flow is regulated through a regulator valve. And then, Air passes to the mixing chamber, where the abrasive particle is fed with the help of hoper to the mixing chamber.
- Here to note that The size of abrasive particle should be 0.001 inches or 0.025mm.
- Abrasive power and compressed air are thoroughly mixed in the mixing chamber, where the vibrator controls the feed rate of abrasive particles, placed beneath the mixing chamber.
- Now, Pressurized air mixed with abrasive particles sends to the nozzle. Here nozzle increases the velocity of the mixer and expands its pressure.
- All the pressure energy of the jet is converted into velocity outside the jet and the High-velocity jet hits the work surface to remove the unwanted materials from the workpiece.
This is how Abrasive jet machining works.
Fig.- Diagram of Abrasive jet machining
The parameters that influence the rate of metal removal rate(MRR) and accuracy of the machining in this process are-
- Carrier gas
- Types of abrasive
- Size of abrasive grain
- Velocity of abrasive jet
- Work material
- Nozzle design
(I) Carrier gas-
The carrier gas, to be used in AJM, must not flare excessively when discharged from the nozzle into the atmosphere. Further, the gas should be non-toxic, cheap, easily available and capable of dried and cleaned out without difficulty.
The gas used in the abrasive jet machining is generally- air, carbon dioxide or nitrogen. Air is most commonly and widely used owing to easy availability and little cost.
(II) Types of abrasive-
The choice of abrasive depends on the type of machining operation. For example, roughing, finishing, work material and cost.
In the abrasive jet machining process, the abrasive particles should have a sharp and irregular shape and be fine enough to remain suspended in the carrier gas and should have also flow characteristics.
The abrasives used for cutting are aluminium, oxide and silicon carbide, whereas sodium bicarbonate, dolomite, glass beads, etc. are used for cleaning, etching, deburring and polishing.
Re-use of abrasives is not recommended because it decreases the ability to cut.
(III) Size of abrasive grain-
The rate of metal removal depends on the size of the abrasive grain. Finer grains are less irregular in shape, and hence, have lesser cutting ability. Moreover, finer grains tend to stick together and choke the nozzle.
(IV) Velocity of abrasive jet-
The kinetic energy of the abrasive jet is utilized for metal removal by erosion. The jet must touch the work surface with a certain minimum velocity.
The minimum jet velocity has been found to be around 150 m/s.
(V) Work Material-
AJM is recommended for the processing of brittle materials, such as glass, ceramics, refractories, etc. Most of the ductile materials are practically un-machined by AJM.
(VI) Nozzle design-
The nozzle has to resist the erosive action of abrasive particles, and hence, must be made of materials that can provide high resistance to wear.
The common materials for the nozzle are sapphire and tungsten carbide.
Metal Removal Rate-
Taking into consideration the fact that metal removal is due to the chipping of the work surface brought about by the impacting abrasive particle.
The metal removal rate(Q) of AJM can be obtained by the following equation or formula, Given below-
Are you there?
After going through various topics of AJM, Now it’s time to move to the Advantages, disadvantages and applications of AJM.
So, are you ready?
If so, Then here we go…
Advantages of Abrasive jet machining-
Here are some advantages of AJM. Given below-
- Hard and brittle materials machining
- Negligible surface damage
- Little or no heat generation
- Low capital investment
- Low power consumption
Disadvantages of Abrasive jet machining-
Here are some disadvantages of AJM. Given below-
- Poor machining accuracy
- High nozzle wear rate
- Restricted to hard and brittle materials
- Additional operation of cleaning sometimes
- Environment pollution
Applications of Abrasive jet machining-
Here are some Applications of AJM. Given below-
- Removing flash and parting lines from injection moulded parts.
- Deburring and polishing plastic, nylon and Teflon components,
- Cleaning metallic mould cavities which otherwise may be inaccessible.
- Cutting thin sectioned fragile components made of glass, refractories, ceramics, mica, etc.
- Producing high-quality surfaces.
- Removing glue and paint from paintings and leather objects.
- Reproducing designs on a glass surface with the help of masks made of rubber, copper, etc.
- Frosting interior surface of glass tubes.
- Etching markings on glass cylinders.
The abrasive jet machining process can be used to remove excess material from hard and brittle materials. Ductile materials have a lower machining rate through AJM, However, I discussed in detail above.
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Abhishek Tiwary is a blogger by passion and a Quality Engineer by profession. He has completed his B.Tech degree in the year of 2017. Now working in a reputed firm and He loves to share his knowledge with others.