ELECTRICAL DISCHARGE MACHINING

1. Electric Discharge Machining
SUBMITTED BY
Name- Jagabandhu Sahoo
Branch – Manufacturing Engineering

2. Introduction
• Electrothermal process
• machines hard material which are electric conductive in nature
• Machines material using spark discharge
• Also called as Spark erosion ,Die sinking

3. Process Principles

4. Working principle
• positive terminal of power supply is connected to workpiece and the
negative terminal is applied to the tool or electrode.
• a potential difference is applied an electric field is established
between the tool and workpiece which will pluck the free electrons
from the tool in large number and they are accelerated towards the
workpiece because of large electrostatic force of field .Thus there will
be collision of electron with dielectric molecules.
• As the electrons are highly energetic they will ionise the dielectric
molecule. After the primary collision the electrons are again
accelerated which leads to the more and more collision and creates a
plasma channel between tool and workpiece

5. Working principle
• workpiece will be continuously impinged by electrons and on
impingement the associated kinetic energy get changed into thermal
energy causing localised melting leading to material removal in form
of debris which is continuously being flush off by the dielectric.

6. Equipment
1. D.C POWER SUPPLY
2. Dielectric System
3. Electrode
4. Servo system

7. Power supply
• Transforms AC from main utility electric supply to pulsed dc.
• Senses the voltage between the electrode and workpiece
• It controls pulse voltage ,current,pulse duration,duty cycle ,pulse
frequency and electrode polarity
• Cutoff or fault protection circuit is there in power supply to protect
against short circuit between the electrode and workpiece due to
over voltage ,overcurrent

8. Dielectric system
• Consists of Dielectric fluid, delivery device, pumps and filters
• High viscosity and high electrical resistance fluid is used electrolyte
• acts as insulator between the electrode workpiece
• Acts as coolant to draw away the heat generated by the sparks
• As a flushing medium to remove the metal byproduct from the
gap.

9. Flushing techniques

10. Requirements of electrode material
• Readily available
• Machinable
• Low wear
• Electrically conductive
• Good surface finish n w/p
Common Materials
1.Copper
2.Brass
3.graphite

11. Servo system
• Controls the feed of electrode or workpiece
• Touch off sensing ,break through sensing
• Electrode refeed

12. Characteristics of EDM
• Mechanism of process Controlled erosion (melting and evaporation)
through a series of electric spark
• Spark gap 0.010- 0.500 mm
• Spark frequency 200 – 500 kHz
• Peak voltage across the gap 30- 250 V
• Metal removal rate (max.) 5000 mm3/min
• Specific power consumption 2-10 W/mm3/min
• Dielectric fluid EDM oil, Kerosene liquid paraffin, silicon oil, deionized
water etc.
• Tool material Copper, Brass, graphite, Ag-W alloys, Cu-W alloys
• MRR/TWR 0.1-10
• Shapes Micro holes, narrow slots, blind cavities.
• Limitations High specific energy consumption,
non-conducting materials can’t be machined.

13. Process parameter
Effect of current

14. Effect of pulse on time on mrr and surface roughness

15. Effect of frequency on surface roughness

16. Effect of electrode and
w/p gap
• Gap is determined b the sark
voltage and current
• Gap values : 0.012 to 0.050 mm
• Smaller the gap ,better accuracy
,surface finish and slower the
mrr
On increasing the pulse duration
of the sparks .
• increases the mrr
• Increases surface roughness
• Decreases electrode wear
Effect of pulse duration
of sparks

17. Process capabilities
• Drilling o irregularly shaped hole ,slots and cavities
• drill holes of multiple dia simultaneously
• Precision process with accuracies of +_0.025 - +_0.127mm can
achieved
• Drilling holes up to aspect ratio 30:1 ,
• Angle as shallow as 20 degree can be drilled
• Volume mrr is 0.016-16cm³/hr.

18. Application
• Drilling of micro holes, thread cutting ,helical profile milling ,curved
hole drilling
• Cooing holes in super alloy turbine blades
• Machining of fragile and slender work without any distortion
• Deep cavities ,slots and ribs can be easily made by EDM for collets ,jet
engine blade slots
• Micro EDM process can produce micro pins micro nozzles and micro
cavities

19. Advantages
• No cutting force
• Burrless
• High hole drilling aspect ratios
• High accuracy
• Intricate cavity
• Any hard material can be
machining
Disadvantages
• Low removal rates
• Electrode consumable
• Limited to electrically
conductivity material
• Produce recast and heat affected
zone
• Complex electrodes can require
long lead time for fabrication

20. Conclusion
In the metal cutting, EDM has been a viable machining option for
producing highly complex parts, independent of the mechanical
properties of work piece material.
The capacity of machining hard and difficult to machine
parts has made EDM as one of the most important machining
processes. Absence of mechanical stresses via the nonexistence of
direct contact between tool and work piece makes it more prominent
machining operation especially for brittle structures.

21. References
[1] Singh S, Maheshwari S, Pandey P C (2004) Some investigations into the electric
discharge machining of hardened tool steel using different electrode materials. Journal of
Materials Processing Technology, 149:272-277.
[2]Ramani V, Cassidenti M L (1985) Inert gas Electrical discharge machining, Nasa Technical
brief number NPO 15660
[3] Luis C J, Puertas I, Villa G (2005) Material removal rate and electrode wear study on the
EDM of silicon carbide. Journal of Materials Processing Technology, 164–165:889–896.
[4] Bojorquez B, Marloth R T, Es-Said O S (2002). Formation of a crater in the workpiece on
an electrical discharge machine. Engineering Failure Analysis, 9:93–97.
[5] Ho K H, Newman S T (2003) State of the art electrical discharge machining (EDM).
International Journal of Machine Tools & Manufacture, 43:1287–1300.
[6] Rajurkar K P (1994) Handbook of Design, Manufacturing and Automation, Non-
traditional Manufacturing Processes, Wiley, USA.

22. THANK YOU