ELECTRICAL ENERGY BASED PROCESSES

1. RAMCO INSTITUTE OF TECHNOLOGY
Mr.M.LAKSHMANAN
Assistant Professor (Senior Grade)
Department of Mechanical Engineering

2. UNIT III
ELECTRICAL ENERGY BASED
PROCESSES

3. Principle
The heat energy available in the electric spark is
used to remove the material from the
workpiece.
Whenever a spark is developed between two
electrical contacts a small amount of material
is removed from each contact.
• Electrical Discharge Machining (EDM)
• Wire cut Electrical Discharge Machining
(WC EDM)

4. Electrical Discharge Machining
(EDM)
PRINCIPLE:
EDM / spark erosion machining / Electro
erosion machining , metal is removed by
producing powerful electric spark discharge
between the tool(Cathode) and the work
piece (Anode).

7. Characteristics
• Voltage – Greater than 250V
• Spark Interval – 10 to 30 Microseconds
• Current Density – 15 to 500A/mm2
(1000 spark discharge occurs per seconds.)
• Temperature during process – 10,000˚C.
• Dielectric Fluid – Petroleum based
Hydrogen fluids, paraffin, white spirit,
Transformer oil, Kerosene, Mineral oil, etc.,

8. DIELECTRIC FLUID
• It’s a medium that does not conduct
electricity.
• Its must circulate freely between tool and
work piece.
• The eroded particles should be flushed out
at the earliest since it reduces the further
metal removal rate.

9. Types of Flushing
1. Pressure Flushing:

10. 2. Suction Flushing:

11. 3. Side Flushing:

12. Function of Dielectric Medium
• Its acts as an insulating medium.
• It cool 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.

14. Tool Material (Electrode) and
Tool Wear
• Metallic Materials – Copper, Brass, copper-
Tungsten
• Non metallic materials – Graphite
• Combination of Metallic & Non metallic –
Copper-Graphite
Wear Ratio = Volume of work material removed
Volume of electrode consumed

15. • Brass Electrode – 1:1
• Copper – 2:1
• Copper Tungsten – 8:1
• Non Metallic (graphite) – 5:1 to 50:1

16. MRR and Surface Finish
• MRR up to 80mm3/s.
• Surface Finish 0.25micro meter
• Rough Process = +/- 0.05 to 0.13mm
• Fine Process = +/- 0.003 to 0.013mm

17. Factors Affecting MRR
• MRR increases with forced circulation of
dielectric fluid.
• It increases up to optimum value of work –
tool gap, after that it drops suddenly.
• MRR is maximum when the pressure is
below the atmospheric pressure.

18. Power Generation Circuits / Spark
Generating Circuits
• Resistance – Capacitance Circuit (RC Circuit)
or Relaxation Circuit
• R-C-L Circuit
• Rotary Pulse Generator Circuit
• Controlled Pulse Generator Circuit

19. Relaxation Circuit
Energy Released per spark = E = ½ C.Vd 2
Where
C= Capacitor Value
Vd= Discharge Voltage
= Vo [1-exp[-t/Rc]]
Vo = D.C source voltage

20. Relaxation Circuit

21. R-C-L Circuit

22. Rotary Pulse Generator

23. Controlled Pulse Generator Circuit

24. Process parameters
• Operating Parameters
• Taper
• Surface Finish
• Current Density

25. 1.Operating Parameters
• MRR = ɸ(E) f
= ɸ ʃvi dt
Where
ɸ - Function
E – Electrical Energy
V – Voltage
i – Instantaneous current
dt – Time interval
f – Torque
ῑp – Pulse width
Tool Wear rate (TWR) = Ѱ (E)f = Ѱ ʃvi dt
ῑp

26. MRR and TWR Based on
• Energy content of the pulse
• Rate of energy supplied
• Servo sensitivity
• Gap width
• Dielectric parameters

27. Types of Wear in Tool
• End Wear
• Corner Wear
• Side Wear

29. 2.Taper

31. 3.Surface Finish
Surface finish of the material depends upon
the following factors
i. Energy of the pulse
ii. Frequency of operation

32. 4.Current Density
• It is affected by either changing current or
changing the electrode (tool) – work piece
gap.
• When the current is increased, each
individual spark removes a larger piece of
metal from the work piece. But its also
increases surface Roughness.

34. • Electrical Discharge Machining
https://www.youtube.com/watch?v=L1D5DLW
WMp8
• Electro discharge machine (EDM)
https://www.youtube.com/watch?v=2W4xZYRk
WGo
• Electrical Discharge Machining EDM
https://www.youtube.com/watch?v=k646HE6M
xE4

35. Advantages of EDM Process
• It can be used for machining various
materials like, Tungsten Carbides,
Electrically conductive materials and other
hard materials.
• It gives good surface finish.
• Machining of very thin section is possible.
• It is well suited for complicated
components.
• There is no cutting forces act on the job.

36. • High accuracy is obtained.
• Fine holes can be easily drilled.
• Its quicker process.
• The process once setup does not need
constant operators attention.

37. Disadvantages
• Its only used for machining electrically
conductive materials.
• Its suitable only for machining small work
pieces.
• Electrode wear and over cut are serious
problems.
• Perfectly square corners cannot be made by
EDM process.
• Power requirement is very high.

38. Applications
• Production of complicated and irregular
shaped profiles.
• Thread cutting in jobs.
• Drilling of micro holes.
• Helical profile drilling.
• Curved hole drilling.
• Re sharpening of cutting tools.

40. • Electrical discharge machining - Video
Learning - WizScience.com
https://www.youtube.com/watch?v=7Ln_l5bXx6
U

41. WIRE CUT ELECTRO DISCHARGE
MACHINING (WCEDM) or TWEDM
• A very thin wire (0.02 to 0.3mm) made of
brass or molybdenum having circular cross
section is used as a electrode (Tool).
• The wire is stretched and moved between
two rollers.
• The part of wire is eroded by the spark.
• Complicated cutout can easily machined.

42. Construction of WCEDM
It consist of,
i. Work piece movement control unit.
ii. Work piece mounting Table
iii. Wire drive section
iv. Dielectric fluid supply
v. Power supply unit

44. Characteristics of WCEDM
• Material Removal Technique: By using
Powerful electric spark
• Work material : Electrically conductive
materials and alloys
• Tool Material : Copper, Yellow Brass,
Alloy of Zinc, Copper
Tungsten, molybdenum
• MRR : 15 to 80 mm3/s
(2 to 400mm3/min)
• Spark Gap : 0.005 to 0.05mm

45. • Spark Frequency : 200 to 500 KHz
• Spark interval : 10 to 30 microseconds
• Volts : 30 to 250 V
• Current : 5 to 60A
• Current density : 15 to 500A/mm2
• Temperature : 10,000˚C
• Dielectric Fluid : Petroleum based
hydrocarbon fluids, Parafin,
White spirit, etc.,
(Distilled water)
• Wire feed : 10 to 30mm/s
• Surface Finish : 0.05 to 12.5 microns

46. Process parameters
• Spark on time
• Spark off time
• Spark Gap
• Discharge current
• Voltage

47. S.
No.
Wire cut EDM EDM
1. Very thin wire made of
molybdenum or brass is
used as the electrode (tool).
Alloy of silver and Tungsten
is used as the electrode
(tool).
2 Whole workpiece is not
submerged in dielectric
medium.
Whole workpiece is
submerged in dielectric
medium.
3 Its easy to machine complex
two dimensional profiles.
Its difficult to cut complex
two dimensional profiles.

48. • Wire EDM NC test cutting a cat, part 2
https://www.youtube.com/watch?v=vYiPRm-
HBWM
• How Wire EDM Works
https://www.youtube.com/watch?v=pBueWfzb7P0
• Wire EDM Animation.flv
https://www.youtube.com/watch?v=RFm9V-NtC3w
• Wire EDM
https://www.youtube.com/watch?v=IewSHORZTJ8