Abrasive flow machining, chemo-mechanical polishing, magnetic abrasive finishing, magneto rheological finishing, magneto rheological abrasive flow finishing their working principles, equipments, effect of process parameters, applications, advantages and limitations.

1. UNIT -4
CHEMICAL AND ELECTRO-CHEMICAL
ENERGY BASED PROCESSES

2. 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

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

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

5. Chemical Machining

6. Processes in CM
Cleaning
Drying
Maskant coating
Dipping in chemical solution
Stirring & Heating – For Uniform Depth
washing

7. 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

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

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

10. Dipping in Chemical solution
• Caustic soda - Aluminium
• Hydrochloric acid and nitric acid – steel
• Iron chloride – 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

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

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

13. ETCHANT (CHEMICAL SOLUTION)

14. MASKANTS

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

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

17. Maskant
.

18. 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 working material

19. 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

20. .
.

21. CLASSIFICATION OF CHEMICAL MACHINING
PROCESSES
CONTOUR MACHINING
• Material is etched entirely on the workpiece
• Used for cutting parts from thin sheet metals or foil
sheets
• Material is etched selectively on the workpiece
• Used for removing metal from thicker workpiece

22. ADVANTAGES OF CHM
• Burr-free components are produced.
• Most difficult to machine materials can be
processed.
• High surface finish is obtained.
• Stress free components are produced.
• Hard and brittle materials can be machined.
• Complex contours can be easily machined.
• Any metal can be machined.
• There is no need of skilled labour.
• Both faces of workpiece can be machined
simultaneously.

23. DISADVANTAGES OF CHM
• Since the process is slow, metal removal rate is
low.
• Manufacturing cost is high.
• Large floor area is needed.
• It is not possible to produce sharp corners.
• Workpiece thickness can be machined, is limited.

24. APPLICATIONS OF CHM
• Chemical machining process is applied in great
number of usages where the depth of removal is
critical to a few microns and the tolerances are
close.
• The major application of chemical machining is in
the manufacture of burr free components.

25. Electro-chemical Machining (ECM)

26. 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

27. Basic electroplating concept
• Things to be coated to Negative terminal (Cathode)
• Electrode is connected to positive Terminal
(Anode)

28. ECM – REVERSE OF
ELECTROPLATING
Our objective is - Metal should be removed
from the work piece
So work piece to 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

29. .
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

30. 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

31. Analysis of Metal Removal
• Electrolysis Process

32. Anodic Dissolution

36. FACTORS AFFECT THE CURRENT FLOW
• Gas evolution (H2) at the electrode surface may reduce
the current flow.
• Polarizes ionic layers may build up at electrode, causing
large voltage drop neat the surfaces.
• When electrolyte is heated more, it results in boiling.
It automatically reduces the electrolytic action.

37. ECM tool material properties

38. ELECTROLYTE
• It carries the current between tool and the
workpiece.
• It cools the cutting zone which becomes hot
due to the flow of high current.
• It removes products of machining from the
cutting zone.

39. ELECTROLYTE USED

40. ADVANTAGES OF ECM PROCESSES

41. ADVANTAGES OF ECM PROCESSES

42. DISADVANTAGES OF ECM PROCESSES

43. APPLICATIONS OF ECM

44. DEFFERENCE BETWEEN EDM AND ECM

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

46. 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

47. Electro-chemical Grinding
Work Piece
+Ve Terminal
Grinding Wheel
- Ve Terminal
D.C.Voltage 3 – 30 V

48. Gap 0.025mm
ELECTROLYTE
Sodium Nitrate
Sodium Chloride
Potassium Nitrate
+ Water

49. Grinding Wheel – made up of fine Diamond
wheel
Grinding wheel speed
900 – 1800 m/min

50. Process Parameters
• Current density
– 100 to 200 A/cm², DC voltage= 3 to 30V
• Electrolyte
– 0.150 to 0.300 kg/litre of water, Temp= 15°C to 30°C
• Feed rate
– Maximum depth of cut for grinding wheel = 2.5mm
• Grinding wheel speed
– 900 – 1800 m/min

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

56. Work Piece + Ve Terminal (Anode)
Tool -Ve Terminal (Cathode)
Gap = 0.075 to 0.125 mm
Electrolyte Supply = 112 lit/min, Pressure=1.05 N/mm²
Voltage = 25 V
Tolerance = 0.012 to 0.005 mm

57. 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

59. Electrochemical Deburring:

60. Process
• Designed to remove burrs or to round sharp
corners on metal workpieces by anodic
dissolution method.
• The hole in the work part has a sharp burr of
the type that is produced in a conventional
through-hole drilling operation.

61. • The electrode tool is designed better to focus
the metal removal action on the burr.
• Surface portions of the machining tool not
being used for machining are insulated.
• The electrolyte material flows through the
hole to carry away the burr particles.