Chemical machining and Electro-Chemical machining (CHM and ECM)- Etchants – Maskant - techniques of applying maskants - Process Parameters – Surface finish and MRR-Applications. Principles of ECM- equipments-Surface Roughness and MRR Electrical circuit-Process Parameters- ECG and ECH - Applications.

1. UNIT-3
ELECTRICAL ENERGY BASED
PROCESSES

2. WORKING PRINCIPLE
• Metal is removed by producing powerful
electric spark discharge between the tool
(cathode) and the work material (anode).

3. MAIN COMPONENTS
• Electric power supply
• Dielectric medium
• Work piece
• Tool
• Servo control mechanism

4. CONSTRUCTION
• Electric power supply (D.C power supply)
• Dielectric medium (paraffin, white spirit or
transformer oil) – poor electrical conductivity
• Work piece - Submerged in a dielectric medium
• Tool
• Servo control mechanism (maintain “spark gap”
ranges of 0.005 to 0.05 mm)

5. WORKING
• D.C supply is given to the circuit.
• Spark is produced across the gap b/w the tool and the
workpiece.
• Voltage across the gap is more than 250 V
• Dielectric breaks down and electrons are emitted from
cathode and the gap is ionized.
• Spark occurs in an interval of 10 to 30 microseconds.
• Current density 15-500 A per mm2
• Temperature raises upto 10,000° C

6. • At this high pressure and temperature, workpiece metal is
melted, eroded and some of it is vaporised.
• If Anode and cathode are made of same material greatest
erosion takes place at the anode.
• To remove maximum metal and have minimum wear to tool,
the tool is made as cathode and the workpiece as anode.

7. .

8. SPECIFICATIONS
Voltage = 250 V
GAP = 0.005 – 0.05 mm
Temperature = 10000 degree celcius
Spark occur = 10 – 30 micro seconds
Current density = 15 – 500 A

9. DIELECTRIC FLUID
• It is a medium that does not conduct electricity.
• In EDM process the tool and workpiece are submerged
in a dielectric fluid medium.
• Dielectric fluids are petroleum based hydrocarbon
fluids, paraffin, white spirit, transformer oil, kerosene,
mineral oil or mixture of these.
• Dielectric fluids must not be hazardous to operators or
corrosive to equipment.
• Dielectric fluids is chosen depends upon the workpiece
size, type of shape, tolerance, MRR and surface finish.

10. • White spirit is best suited for machining tungsten
carbide.
• The dielectric fluids must circulate freely b/w the tool
and workpiece.
• The eroded particles should be flushed out at the
earliest since it reduces the further MMR.

11. Dielectric Fluid
Petroleum Products
Paraffin
White sprit
Transformer oil
Kerosene
Mineral oil
Mixture of all
Dielectric Fluid Requirements
•Should not be toxic
•Should not be corrosive
•Should not be hazardous
•Should be circulate freely
•Should be flushed out
•Should be act as coolant
• Should be filtered before use
•Should be less cost

12. Di electric Fluid – Flushing Method
1. Pressure Flushing
2. Suction Flushing
3. Side Flushing

13. Pressure Flushing
Di electric Fluid – Flushing Method

14. Suction Flushing
Di electric Fluid – Flushing Method

15. Side Flushing
Di electric Fluid – Flushing Method

16. Functions of Dielectric Fluid

17. TOOL MATERIAL AND TOOL WEAR
 Tool materials classified as
 Metallic materials (Copper, Brass, Copper-
tungsten)
 Non – metallic materials (Graphite)
 Combination of metallic and non-metallic (copper
- graphite)
 Copper for fine machining, aluminium for die-
sinking and cast iron for rough machining.

18. BASIC REQUIREMENT OF ANY TOOL
MATERIAL
• It should have low erosion rate.
• It should be electrically conductive.
• It should have good machinability.
• Melting point of the tool should be high.
• It should have high electron emission.

19. TOOL WEAR
Wear ratio =
Volume of work material removed
Volume of electron consumed
• For brass electrode is 1:1
• For copper electrode is 2:1
• For copper tungsten is 8:1
• Non metallic (graphite) vary from 5:1 to 50:1

20. POWER GENERATING CIRCUITS
SPARK GENERATING CIRCUITS
OR
AC Current DC Current
Rectifier is used to convert AC to DC

21. Types

22. 1. Relaxation Circuit
• Commonly used
• Simplicity
• Less cost

24. Dis-advantages

25. 2. R-C-L Circuit
• MRR increases with the decrease of R
Capacitor charging
time is the problem
in R-C circuit.
So to overcome this
, inductance (L) is
introduced in the
circuit

26. Rotary Pulse Generator
• R-C and R-C-L yield low MRR
• Rotary Pulse Generator over come Drawback
of above to circuits
• It give high MRR
• It give good Surface finish
• It give low tool wear
• It provide better control in all Parameters

27. Rotary Pulse Generator
• Here Capacitor is discharged through the diode during first half
cycle.
• In the next half cycle sum of voltages is given with charged
capacitor to the circuit.
• So high spark produced
• It results high MRR
Draw Back
•Poor Surface Finish

28. Controlled Pulse Generator Circuit
• All above three circuits not having any safety
incase of Short circuit in the circuit
Here in this a vacuum tube
(Transistor) is provided as an
automatic control

29. PROCESS PARAMETERS
.
EDM

30. 1. Operating Parameters
2. Taper
3. Surface finish
4. Current Density
PROCESS PARAMETERS

31. • Operating Parameters
PROCESS PARAMETERS
Tool Wear Rate
Tooling cost
Accuracy
Working Time
Used to calculate

32. • Operating Parameters
PROCESS PARAMETERS
Types of wear
1.End Wear
2.Corner Wear
3.Side wear

33. • Taper
PROCESS PARAMETERS
Due High dielectric Pollution , side sparks are more than
front spark. So Tapering Occur in Hole

34. • Surface Finish
PROCESS PARAMETERS
It Depend on
i) Energy of Pulse
ii) Frequency of operation

35. • Current Density
PROCESS PARAMETERS
Current
Density
(More
Spark)
= MRR + Surface
Roughness
Current
Density
(Less
Spark)
= MRR + Surface
Roughness
Good Surface Finish
Poor Surface Finish

36. Advantages
of EDM

37. Dis-advantages of EDM

38. Applications of EDM

39. Wire – Cut EDM (WEDM)
Travelling Wire Cut EDM (TWEDM)
0.02 – 0.3mm dia wire
Wire - Brass or Molybdenum
10 – 30 micro second sparking
15 – 500 Amp / mm²
30 - 250 V
10,000 ̊C - Temperature
10 – 30 mm/ sec wire Feed
15 – 80 mm³ / sec MRR
Petroleum Based Hydrocarbon
Fluids – Paraffin, white Sprit ..

40. Features of WCEDM
i) Manufacturing Electrode
ii) Electrode Wear
iii) Surface Finishing
iv) Complicated Shapes
v) Time Utilization
vi) Straight Holes
vii) Rejection
viii)Economical
ix) Cycle Time
x) Inspection Time

41. Disadvantages of WEDM
• High Capital cost
• Cutting Rate is slow
• Not suitable for large work pieces

42. Applications of WEDM
• In the manufacturing of
Gears
Tools
Rotors
Turbine Blades
Cams

43. Wire Cut EDM Vs EDM

44. APPLICATIONS