ELECTRICAL DISCHARGE MACHINING
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ELECTRICAL DISCHARGE MACHINING
DIAGRM OF EDM
WORKING PRINCIPLE OF EDM

 In electrical discharge machining , metal is removed by producing powerful electrical spark discharge between the tool (cathode) and the work material 9anode). It is also known as spark erosion machining or electro-erosion machining….
CONSTRUCTION AND WORKING OF EDM
 Construction:
 The main components are the electrical power supply ,dielectric medium , work piece , tool and a servo control mechanism.
 The work piece and the tool are electrically connected to a d.c supply .
 The work piece is connected to the positive terminal of the electric source, so that it becomes anode. The tool is connected to the negative terminal of the electric source so that it becomes the cathode.
 The tool and work piece are submerged in a dielectric fluid medium such as paraffin, white spirit or transformer oil having poor electrical conductivity.
 the function of the servo mechanism is to maintain a very small gap known as ‘spark gap’ range of 0.005 to 0.05 mm between the work piece and the tool.
WORKING
 When the d.c supply is given to the circuit , spark is produced across the gap between the tool and the work piece.
 When the voltage across the gap becomes sufficiently large (more than 250v), the high spark is produced.
 This spark occur in interval of 10 to 30 microseconds and with a current density of 15-500A per mm^2 approximately . Which results in increasing temperature of about 10,000 deg centi.
 At this high pressure and temperature , work piece metal is melted , eroded and some of it is vaporized. In this way the metal is removed from the work piece .
 The removed fine material particles are carried away by dielectric fluid circulated around it.
 The metal removal rate depends on the spark gap maintained. If anode and cathode are made of same material , it has been cathode are made of same material ,it has been found that the greatest erosion takes place and anode.
 When the voltage drops to about 12 volts ,the spark discharge extinguishes and the dielectric fluid once again becomes deionizer .
DIELECTRIC FLUID
 A dielectric fluid is a medium that dose not conduct electricity. In electrical discharge machining process ,the tool and work piece are submerged in a dielectric fluid medium. The fluids generally used are petroleum based hydrocarbon fluids, paraffin , white spirit, transformer oil , mineral ail or mixture of these..
 Dielectric fluids must not be hazardous to operators or corrosive to equipment.
 The choice of any dielectric fluid depends upon the work piece size, type of shape , tolerance , metal removal rate and surface finish. White spirit is best suited for machining tungsten carbide .
 The dielectric fluid should not be changed frequently on a machine ,and it is chosen according to the most frequently application to be carried out in the machine .
 The dielectric fluid must circulate freely between the tool and work piece.
 The eroded particles should be flushed out the earliest since it reduces the further metal removal rate.
 The various methods of flushing are pressure flushing suction flushing and side flushing which are shown in.
 The dielectric fluid should be filtered before reuse so that chip contamination of the fluid will not affect machining accuracy.
 The dielectric fluid should be easily available at reasonable price.
FUNCTION OF DIELECTRIC FLUIDS
 It acts as an insulating medium.
 It cools the spark region and helps in keeping the tool and work piece cool.
 It carries away the eroded metal particles along with it.
 It maintains a constant resistance across the gap.
 It remains electrically non conducting until the required breakdown voltage has been reached.
 It breakdown electrically in the shortest possible time once the breakdown voltage has been reached.
Advantages of edm process
 It can be used for machining various materials such as tungsten carbides, electrically conductive materials, and other hard materials.
 It gives good surface finish.
 Machining of very thin section is possible.
 It does not leave any chips or burrs on the work piece.
 it is well suited for complicated components.
 Since there is no cutting forces act on the job, error due to elastic deformation is eliminated.
 High accuracy is obtained.
 Fine holes can be easily drilled.
 It us a quicker process. So, harder materials can also be machined at much faster rate than conventional machining.
 The process once setup does not need constant operators.
Disadvantages of edm process
 It is only used for machining electrically conductive materials. So non- metallic such as plastics, ceramics or glass can not machined by EDM.
 It is suitable only for machining small work pieces.
 Electrode wear and over cut are serious problems.
 Perfectly square corners cannot be made by EDM process.
 Metal removal rate is slow.
 Power requirements is very high.
 In many cases, the surface machined has been found to have micro cracks.
applications
 Production of complicated and irregular shaped profiles.
 Thread cutting in jobs.
 Drilling of micro holes.
 Helical profile drilling.
 Curved hole drilling.
 Resharpening of cutting tools and broachers.
 Remachining of die cavities without annealing.
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http://studentbank.in/report-electrical-...-machining

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