UCM-UNIT-3-CHEMICAL AND ELECTRO-CHEMICAL ENERGY BASED PROCESSES

1. UNIT -III
CHEMICAL AND ELECTRO-CHEMICAL
ENERGY BASED PROCESSES

2. TOPICS
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.

3. INTRODUCTION
• The metal is removed from the work piece
through controlled etching or chemical attack
of the work piece material in contact with a
chemical solution

4. CHEMICAL MACHINING
In this method , the metal is removed by ion
displacement of the work piece material in
contact with a chemical solution

5. Examples
1. Electro-chemical machining (ECM)
2. Electro-chemical Grinding (ECG)
3. Electro-chemical Honing (ECH)
4. Electro-chemical Deburring (ECD)

6. Chemical Machining

7. Processes in ECM
Maskant coating
Cleaning
Drying
Dipping in chemical solution
Stirring & Heating – For uptain Uniform Depth
washing

8. Maskant Coating
Selective Machining
The selective portions (un-machining areas)
covered by resistant material. called maskants

9. CLEANING
• Trichloroethylene vapour
Or
• Solution of mild alkaline at 85 – 90 degree
celcius
The above solutions are used to remove oil and dust
from the work piece

10. Drying
After cleaning the work piece is dried in air

11. Dipping in Chemical solution
• Caustic soda - for Aluminium
• Hydrochloric acid and nitric acid – for steel
• Iron chloride – for stainless steel
The metal is removed by the chemical conversion of
metal into metallic salt
Dipping time will varies from amount of material to
removed from work piece

12. Stirring & Heating
For obtain uniform depth of metal removal ,
temperature control and stirring of chemical
reagent is important

13. washing
• To prevent further reaction after require
shape obtained, the metal is cleaned properly

14. ETCHANT (CHEMICAL SOLUTION)

15. MASKANTS

16. • Scribed and Peeled Maskants
• Photo resists Maskants
METHODS OF MASKANTS

17. Scribed and Peeled Maskants
For ordinary work piece a paint like material
sprayed or dipped or brushed over the metal

18. Maskant
.

19. Photo resists
Maskants
• For close tolerance and
dimensional accuracy
needed places
• Paint spray type work is
done for preparing
master copy
• The master drawing is
photographed and it
reduced to the size of
the finished part

20. Photo resists
Maskants
• Then the material is
placed over the work
piece.
• And it exposed to UV
light to harden
• Then its dipped in
organic solution for
maskanting.
• Finally it dipped in
chemical solution for
machining

21. .
.

22. .
Electro-chemical Machining (ECM)

23. Principle
Faraday,s Law of Electrolysis
FIRST LAW
Amount of metal deposited directly
proportional to quantity of electricity
SECOND
LAW
Amount of Change in metal is directly
proportional to its electrochemical
equivalent of the material

24. Basic electroplating concept
• So work piece Negative terminal (Cathode)
• Things to be coated is connected to positive Terminal
(Anode)

25. ECM – REVERSE OF
ELECTROPLATING
Our objective is - Metal should be removed
from the work piece
So work piece positive terminal (Anode)
Tool is connected to Negative Terminal (Cathode)
When current is passed , the work piece loses metal
and the dissolved metal is carried out by circulating
an electrolyte between them

26. .
TOOL
- Titanium , stainless steel,
brass and copper
ELECTROLYTE
-Sodium Nitrate
SERVO MOTOR
- To Control Tool Feed
Rate
Tool and Work piece
Gap 0.05 – 0.5mm

27. Electrochemical Machining (ECM)
• Reverse of electroplating
• Work material must be a conductor
• Material removal by anodic dissolution
• Electrical energy + chemical energy
Voltage 5-30 volts
Tool Velocity 30 – 60 m/s
Current 20 -300A/cm2

28. During process -------
• Due to applied voltage, the current flows through
the electrolyte with positively charged ions and
negatively charged ions.
• The positive ions move towards the tool (Cathode)
while negative ions move towards work piece (Anode)
So , Electro-chemical Reaction takes place due to this flow.

29. ELECTRO-CHEMICAL GRINDING (ECG)
OR
ELECTROLYTIC GRINDING
.

30. PRINCIPLE
Machining operation by the combined
action of Electro-chemical effect and
conventional grinding operation
90 % - Metal removed by chemical Action
10 % -Metal removed by Grinding Action

31. Electro-chemical Grinding (ECG)
Work Piece
+Ve Terminal
Grinding Wheel
- Ve Terminal
D.C.Voltage 3 – 30 V

32. Gap 0.025mm
ELECTROLYTE
Sodium Nitrate
Sodium Chloride
Potassium Nitrate
+ Water
Grinding Wheel – Fine Diamond Particle
Grinding Wheel speed – 900 -1800 m/min

33. PROCESS PARAMETERS
1. Current Density
100 – 200 A / cm2
The MRR increases with the Increase of Current
Density – which results high Surface Finish

34. PROCESS PARAMETERS
2. Electrolyte
Sodium Nitrate
Sodium Chloride
Potassium Nitrate
The MRR increases with the correct composition
of electrolyte with water – which results high
Surface Finish
Maintained at a Temperature
of 15 – 30 Degree Celcius

35. PROCESS PARAMETERS
3. Feed Rate
Slow feed Poor Surface Finish
High feed Excess Tool Wear –
Poor Surface Finish
Optimum feed Good Surface Finish

36. ADVANTAGES OF ECG
1. Life of the grinding wheel is high (because 90% material
removed by chemical process)
2. No heat is produced in the process so the work surfaces
are free from cracks.
3. Less cutting force only required
4. Good surface finish is obtained.
5. Work material not subjected to any structural changes
6. Burr free and stress free components are made.
7. No Frequent dressing of grinding wheel required.

37. DIS -ADVANTAGES OF ECG
1. High initial cost
2. Power consumption is high
3. MRR is lower than conventional method
4. Non – conducting material cannot be machined.
5. Need safety things for acid usage in process.
6. Maintenance cost is high

38. Applications of ECG
Its best suited for
1. precision grinding on hard materials
2. Cutting of hard material with thin sections
without any damage

39. ELECTRO-CHEMICAL HONING
for Internal grinding
Combined action
of electro-
Chemical attack
and Honing stone
effect

40. MRR is 10 times faster than conventional internal
Grinding
Less tool Wear
Less Pressure is required between Honing tool and
work piece
Burr Free and Stress free Components are produced
Tolerance 0.012mm

41. Work Piece + Ve Terminal (Anode)
Tool -Ve Terminal (Cathode)
Gap = 0.075 to 0.125 mm
Electrolyte Supply = 112 lit /min
Voltage = 25 V

42. Advantages of ECH

43. Problem -1

44. GIVEN DATA

47. PROBLEM-2