ABRASIVE JET MACHINING(AJM)
As explained non traditional machining process involves machining action by indirect contact between tool and work piece. It is a non conventional machining process that performs machining without any contact between tool and work piece.
BASIC IDEA OF ABRASIVE JET MACHINING (AJM)
Abrasive used:-
silicon carbide
aluminium oxide
beads of glass
Diameter of abrasive is about 0.025 mm.
Nozzle made
- Tungsten carbide having life expectancy (12-35 hours).
- synthetic sapphire having life expectancy (up to 300 hours).
Also called as pencil blasting, this process involves projecting high velocity abrasives (silica carbide, aluminium oxide) on the work piece. This high velocity abrasives at speed up to 300 m/s strike the work piece and erodes it. Continuous abrasive action of such abrasives causes continuous deformation of work piece and required shape is obtained.
PROCESS:-
- Highly compressed air or inert gas enters into the filter chamber and impurities are separated.
- There after it is compressed by compressor up to high pressure (170-1000 kpas).
- The pressure gauge and flow regulators check the required pressure and flow of air/inert gas.
- Now the gas enters the mixing chamber, where it gets mixed with abrasives.
- The required pressure is checked and the mixture enters the nozzle.
- The nozzle converts the high pressure mixture to high velocity mixture.
- This high velocity mixture is directed on workpiece and erosion of work material takes place.
ADVANTAGES
- Less heat produced
- Used for non ductile materials.
- Good surface finish.
WATER JET MACHINING
ABRASIVE USED (WATER+GARNET/ALUMINIUM OXIDE)
NOZZLE MADE WITH SINTERED BORIDE
It is another non traditional machining process where there is no contact between tool and the work piece. Water is used as abrasive in such machining .
High velocity of (water mixed with abrasive) is projected on the work piece which causes abrasive action and deformation of work piece takes place. This is basic of water jet machining (WJM).
WATER ALONE CAN BE USED TO CUT SOFT MATERIALS.
BUT WHEN WATER MIXED WITH ABRASIVES IS USED, THIS CAN CUT METALS AND GRANITE ALSO.
FIG:-Diagram of WJM
WORKING PROCESS DESCRIPTION - The water is collected from reservoir by the pump.
- The high pressure pump are capable of producing pressure of 276 MPa to 700 MPa.
- The intensifier and accumulator increases the pressure of the water to the desired limit. Up to (30000-60000 psi).
- The control valve and flow regulator allows desired water to enter the nozzle.
In the nozzle, the abrasive and compressed water is mixed in the nozzle in the mixing chamber. The focusing pipe directs the mixture towards work piece and finally erosion of work piece takes place.
ULTRASONIC MACHINING
BASIC PROCESS:-
- It is process where there is a vibrating tool which oscillates at various frequencies, where further helps to remove material from work piece. This is helped by abrasive slurry which is present between tool and work piece.
ABRASIVE USED
- DIAMOND
- CUBIC BORON NITRIDE (CBN)
- SILICON CARBIDE
- ALUMINIUM OXIDE
TOOL MATERIALS
Tough and ductile materials are generally used as tool material. Tool material should reduce fatigue failure.
- NICKEL
- SOFT STEELS
SLURRY
- Water+abrasive
- Oil+abrasive
A abrasive slurry is concentration of water or oil with abrasive material which is present between the work piece and the tool. It occupies a narrow section between the vibrating tool and work piece. The vibrating tool applies force on the abrasive slurry and abrasive having sharp edge in turn applies force on the work piece which erodes the work piece material. It also carries away the eroded material from cutting section and also keeps the temperature low by carrying away heat.
PROCESS OF MACHINING:-
- The outer source provides power to the transducer and oscillator up to 40 kHz.
- This system provides tool to get directed towards the work piece.
- The amplitude of vibration varies from 0.013 to 0.10 mm.
- The pump sucks the abrasive slurry from reservoir and directs it to cutting action point.
- The high amplitude of vibration or high frequency oscillation creates rapid too and fro motion of tool which pressurizes the abrasive slurry against work piece.
- This causes wear or deformation of work piece.
- Accuracy up to 5 micron can be obtained.
ADVANTAGES:-
- Irregular shapes can be machined.
- Brittle material can be machined
- Good surface finish is obtained.
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