Electric Dischage Machining, Working Principle, Neat diagramme, Advantages, limitations, applications, Process parameters

1. Electric Discharge Machining
J. Hemwani. GPC, Betul

2. J. Hemwani. GPC, Betul

3. J. Hemwani. GPC, Betul
EDM -- Process
▪ (EDM) is an electro-thermal non-traditional machining
process, where electrical energy is used to generate
electrical spark and material removal mainly occurs due to
thermal energy of the spark.
▪ In EDM, a potential difference is applied between the tool
and work piece. Both the tool and the work material are to be
conductors of electricity.
▪ The tool and the work material are immersed in a dielectric
medium. Generally kerosene or de-ionised water is used as
the dielectric medium.
▪ A gap is maintained between the tool and the work piece.

4. J. Hemwani. GPC, Betul
EDM -- Process
▪ Generally the tool is connected to the negative terminal of
the generator and the work piece is connected to positive
terminal.
▪ Thus due to electrostatic forces tool emmitts the free
electrons. These electrons are accelerated toward the work
piece through dielectric.
▪The kinetic energy of the electrons impact with the surface
of the work piece and converted into thermal energy or heat
flux.
▪ This heat flux rises the local temperature. Hence Material
removal occurs due to instant melting and vapourisation of
the work piece material.

5. J. Hemwani. GPC, Betul
EDM -- Process
▪ In EDM, a constant voltage is not applied. But the
generator is used to apply voltage pulses between the tool
and the job.
▪ The material of the work piece metal is partially removed
due to voltage shock waves.
▪Only sparking is desired in EDM rather than arcing because
arcing leads to localised material removal at a particular
point whereas sparks leads to distributed material removal.
▪ Electrons strikes the work piece and positive ions impinge
on the tool leading to tool wear.
▪In EDM, geometry of the tool is the positive impression of
the geometric feature to be machined.

6. J. Hemwani. GPC, Betul

7. J. Hemwani. GPC, Betul

8. J. Hemwani. GPC, Betul
https://www.youtube.com/watch?v=GinrpIvwR
RE&list=PLO5JJ-
e4NcX_1oRnyHTxasz7HvaeFeR80&index=19
Video on EDM 1:44 m

9. Advantages of EDM
✓Any materials that are electrically conductive can be
machined by EDM.
✓ Materials, regardless of their hardness, strength, toughness
and microstructure can be easily machined/cut by EDM
process.
✓ The tool (electrode) and workpiece are free from cutting
forces.
✓ The tool making is easier as it can be made from softer and
easily formable materials like copper, brass and graphite
J. Hemwani. GPC, Betul

10. Advantages of EDM
✓The process produces good surface finish, accuracy and
repeatability.
✓ Hard die materials with complicated shapes can be easily
finished.
✓ Due to the presence of dielectric fluid, there is very little
heating of the bulk material.
J. Hemwani. GPC, Betul

11. Limitations of EDM
▪ Material removal rates are low, making the process
economical only for very hard and difficult to machine
materials.
▪ The EDM process is not suitable for non-conductors.
▪ Rapid electrode wear makes the process more costly.
▪ The surfaces produced by EDM generally have a matt type
appearance, requiring further polishing to attain a glossy
finish.
J. Hemwani. GPC, Betul

12. Applications of EDM
➢ Hardened steel dies, stamping tools, wire drawing and extrusion
dies, header dies, forging dies, intricate mould cavities and such
parts are made by the EDM process.
➢The process is widely used for machining of exotic materials that
are used in aerospace and automotive industries.
➢ EDM is very well suited for making fragile parts like washing
machine agitators, electronic components, printer parts.
➢ It is useful for difficult to machine features such as the
honeycomb shapes.
➢Micro-EDM process can successfully produce micro-pins, micro-
nozzles and micro-cavities.
J. Hemwani. GPC, Betul

13. Process Parameters
➢ Current 0.5 to 400 amp.
➢Voltage (D.C.) 40 to 300 volts
➢ Spark gap 0.0126 to 0.125 mm
➢Di-electric pressure 2 Kg/cm2
➢ Surface Finish Rough 3 to 10 microns and finish 0.8 to 3
microns
J. Hemwani. GPC, Betul

14. J. Hemwani. GPC, Betul