CHEMICAL AND ELECTROCHEMICAL ENERGY BASED PROCESSES

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

2. UNIT IV
CHEMICAL AND
ELECTROCHEMICAL ENERGY
BASED PROCESSES

3. CHEMICAL MACHINING (CHM)
Principle:
The metal is removed from the workpiece
through controlled etching of the workpiece
material in contact with a chemical solution.

4. Procedure
1. The workpiece to be machined is first cleaned
in Trichlorethylene vapour or in a solution of
mild alkaline at 85 to 90 ˚C, followed by
washing in a clean water. This removes dust
and oil from the workpiece.
2. After cleaning, workpiece is dried and coated
with the maskant material.
3. The workpiece is then immersed in a chemical
reagent. So chemical reaction takes place and
the metal is removed from the workpiece.

5. 4. The time of immersion of the workpiece depends
upon the amount of material removed by
chemical action.
5. Caustic soda is used as etching reagent for
aluminium, Solution of Hydrochloric and Nitric
Acids for steel and iron chloride for Stainless
steels.
6. Uniform depth of metal removal based on
Temperature control and stirring of chemical
reagent.
7. After Machining, workpiece should be washed
thoroughly to prevent reaction with any chemical
etching reagent residues.

7. ETCHANTS
The chemical Reagent (Etchant) is used to
remove the metal from the workpiece. The
metal is removed by the chemical
conversion of the metal into metallic salt.

8. Maskant / Resistant
If selective machining is desired the areas of
the workpiece which are not to be machined
are covered with a resistant material called a
Resistant / Maskant.

9. Methods of Masking
• Scribed and Peeled Maskants
• Photoresists Maskants

10. Scribed and Peeled Maskants
• Maskant (Paint) is applied to the entire
surface of the workpiece by dip, spray or
brush.
• After the maskant hardens, its removed
unwanted surfaces by scribing with knife
and peeling away the desired surfaces.
Templates can be used to assist in scribing.
• This method is not suitable for critical
dimensional tolerances.

11. Photoresists Maskants
• Its an excellent method of masking, its used
for complex work in thin surfaces with
closed dimensional tolerances.
1. Cleaned metal is dried and photoresist
material is applied to the workpiece by
dipping, spraying, Brushing or roller
coating.
2. Coating is then dried and hardened by
heating in an oven upto 125˚ C.

12. 3. Master photographic negative is placed
over the dried photoresist coated surface of
the workpiece and exposed to ultraviolet
light, which hardens the exposed areas.
4. After exposure, the workpiece is then
developed by immersing it into a tank
which contains an organic solvent bath
solution. The unexposed portions are
dissolved out during the developing
process, While the exposed portions
remains on the workpiece.

13. 5. Finally the treated workpiece is dipped into
the etching solution. After 5 to 15 minutes
the unwanted metal is removed from the
workpiece and the finished part is washed
thoroughly to eliminate all chemical
residues.

14. • Photo Chemical Machining - Photo Chemical
Etching - Kemac
• https://www.youtube.com/watch?v=xTFqHst
Q42s
• Photo Chemical Machining Process -
Northwest Etch
• https://www.youtube.com/watch?v=NDp3OPI
6dgo
• PCMI - A look into Photo Chemical Machining
• https://www.youtube.com/watch?v=zJmPgA_
aj-k

15. • Chemical Etching Process Video
https://www.youtube.com/watch?v=2HR7qtbXM_4
 Chemical Machining
https://www.youtube.com/watch?v=yG_ZeAEiZ_g
• Photo Chemical Machining Process - Northwest
Etch
https://www.youtube.com/watch?v=NDp3OPI6dgo
&list=PLAXPptxu31u4De78l2eXlat22ibtIbjlA

16. ELECTRO-CHEMICAL MACHINING
(ECM)
This process is based on the principle of
Faraday’s laws of electrolysis which may be
stated as follows:
• The first law states that the amount of any
material dissolved or deposited, is
proportional to the quantity of electricity
passed.
• The second law proposes that the amount of
charge produced in the material is
proportional to its electrochemical
equivalent of the material.

18. CONSTRUCTION

19. 1. Workpiece
2. Tank
3. Tool (Cathode)
4. Servomotor for controlled tool feed
5. D.C. power supply
6. Electrolyte
7. Pump
8. Motor for pump
9. Filter
10.Reservior

21. • Tool Materials are stainless steel, Titanium,
Brass and Copper.
• Electrolytes are Sodium Nitrate, Sodium
Chloride in water, Sodium Hydroxide, Sodium
Sulphate, Sodium Flouride, Pottasium Nitrate
and Pottasium Chloride.
• Tool and work piece are controlled by servo
motor. The gap between work piece is 0.05 to
0.5mm.
• Electrolyte velocity 30 to 60m/s.

22. • D.C. Voltage about 5 to 30 Volts is applied
between the tool and workpiece.
• Current Density 20 to 300A/cm2.
• The electrochemical reaction takes place
due to this flow of ions and it causes the
removal of metal from the workpiece in the
form of sludge.

23. ELECTROLYSIS PROCESS

25. Reaction at cathode (Tool)
Reaction at Anode (Workpiece)

26. W = EIt
F
W – Mass of ions dissolved in Kg
E – Equivalent weight of a substance
dissolved or deposited
I – Current flowing through the
electrolyte cell in Ampheres
t – Time in sec
F – Faraday’s constant = 26.8 Amp.hr
(96,500Columbs)

27. MRR = W
Apt
A – Machined area in m2
P – Density of the workpiece in Kg/m3
MRR = EI/ FAp

28. • The feed rate of electrode
f = V/Psh X E /F P
V = machined voltage in volts
Ps = Specific resistance of electrolyte in
ohm.m
h = Tool work gap in m

29. Factors affecting Current Flow
• Gas evolution (H2) at the cathode surface
may reduce the current flow.
• Polarized ionic layers may build up at
electrode, causing large voltage drops near
the surfaces.
• When electrolyte is heated more, it results
in boiling. It automatically reduces the
electrolytic action.

30. ECM Tool Materials

31. Shape of Tool

32. Tool Design
• Determine the tool shape, so that the
desired shape of the job is obtained under
existing machining conditions.
• Design the tool by considering the
electrolyte flow, insulation strength.

33. ELECTROLYTE
• It carries the current between tool and
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.
• Sodium and potassium salts are commonly
used electrolyte.

35. Characteristics of Electrolyte
• Good conductor of electricity
• Non corrosive property
• Non – Toxicity and chemical stability.
• Low viscosity and high specific heat.

36. Factors affecting Surface Finishing
• Machining Voltage
• Tool Feed Rate
• Temperature of electrolyte
• Concentration of electrolyte
Surface finish 0.2 to 0.8 micron with a
tolerance of 0.005mm.

37. Advantages of ECM Process
• MRR by this process is high compared to
conventional machining.
• Wear and tear of tool is negligible.
• Machining is done at low voltage.
• Intricate and complex shapes can be machined
easily through this process.
• The machined work surface is free of stresses.
• No cutting forces are involved in this process.

38. • High surface finish (0.2 to 0.8microns)
• Very thin sections, such as sheet metal can
be easily machined without any damage.
• Its an accurate process and close tolerances
of the order 0.005mm can be easily
obtained.
• No burrs are produced and this process can
be easily automated.

39. Disadvantages
• Non conducting materials can not be machined.
• Consumption of power is nearly 100 times
more than in turning or milling the steel.
• Machining process is comparatively slow.
• Initial investment is high.
• More space is required.
• To vary the tool feed rate and supply of
electrolyte, constant monitoring is needed.
• Difficulty in designing a proper tooling system.

40. • Sharp internal corners cannot be obtained.
• Post machining cleaning is needed to reduce
the corrosion of the workpieces.

41. Applications of ECM
• Machining complicated profiles such as jet
engine blades, turbine blades, turbine
wheels etc.,
• Drilling small deep holes (Nozzles)
• Machining of cavities and holes of irregular
shapes.
• Machining of forging dies.
• Machining of hard materials and heat
resistant materials.

42. Characteristics of ECM
• Material Removal Technique: Based on
Faraday’s laws of
Electrolysis and
reverse
electroplating.
• Work material: Conducting materials
• Tool Material: Copper, Brass or steel
• Voltage: 5 – 30V
• Current : 50 – 40,000A
• MRR : 27mm3/s

43. • Electrolyte: 20% Nacl solution in water,
Mixture of brine and H2SO4
• Surface finish : 0.2 to 0.8Micrometre
• Tolerance : 0.005mm

46. • ElectroChemical Machining (ECM)
• https://www.youtube.com/watch?v=pI1QGpmKq
ow
• Electro-Chemical Machining(Explain)
• https://www.youtube.com/watch?v=WufD41ww
96E
• How Electrochemical Machining Works
• https://www.youtube.com/watch?v=Ej-
GWNPYFVM
• Electro chemical machining EMAG ECM/PECM -
EMAG Videos
• https://www.youtube.com/watch?v=VzmVrJAIhe
w

47. • Electrochemical machine ECF-A1
• https://www.youtube.com/watch?v=iwbhZab-
iNg
• https://www.youtube.com/watch?v=4ybj-
mS3jRM

48. S.No. EDM ECM
1 Workpiece is submerged in
dielectric fluid
Workpiece need not be
submerged in electrolyte.
2 Tool wear takes place There is no tool wear
3 Control system is required
to maintain constant gap
between tool and
workpiece.
Control system is not
required.
4 Machining can not be done
at low voltages
Machining can be done at
low voltages
5 MRR is slow MRR is high
6 Energy consumed is less Huge amount of energy is
consumed.

49. Problems

52. ELECTRO CHEMICAL GRINDING
(ECG) OR ELECTROLYTIC GRINDING
This work is machined by the combined action
of electrochemical effect and conventional
grinding operation. But major portion of the
metal (90%) is removed by electrochemical
effect.

53. • Sodium nitrate, sodium chloride and potassium
nitrate with a concentration of 0.150 to 0.300
kg/litre of water are usually used as electrolyte
with temperature of 15˚C to 30˚C.
• A constant gap of 0.025mm is maintained
between the grinding wheel and workpiece.
• Grinding wheel is made of fine diamond
particles.
• Grinding wheel runs at a speed of 900 to
1800m/min.
• The workpiece is connected to positive
terminal (Anode) of battery and grinding
wheel is connected negative terminal
(cathode). (Voltage -3 to 30V)

55. Process Parameters
• Current Density
• Electrolyte
• Feed Rate
• Grinding Wheel speed

56. Advantages of ECG
• Tool wear is negligible.
• Work is free of surface cracks and distortion
because heat is not generated in the
process.
• Good surface finish is obtained. (0.2 to
0.4micrometre)
• Burr free stress free components are
produced.

57. Disadvantages
• MRR is lower than conventional machining.
• Non conducting materials can not be
machined.
• Power consumption is high.
• Initial cost is High.
• Maintenance cost is high.
• Preventive measures are needed against
corrosion by electrolyte.

58. Applications
• Very precision grinding of hard metals
Tungsten Carbide tool tips, High speed steel
tools.
• Cutting thin section of hard materials
without any damage or distortion.

60. • VG1000 CNC Electrochemical Vertical Grinde
• https://www.youtube.com/watch?v=9fR1cZ2d
0mQ
• UG824 Ultragrind CNC Electrochemical
Surface Grinder
• https://www.youtube.com/watch?v=fHSUWz
NI96I

61. ELECTROCHEMICAL HONONG (ECH)
• Electrochemical honing is similar to
electrochemical grinding. The work is
machined by the combined action of
electrochemical effect and conventional
grinding operation.
• Uses rotating and reciprocating, non
conducting bonded honing stones instead of
a conducting grinding wheel.
• Most of the metal is removed by
electrochemical effect.

62. • Workpiece is connected to positive terminal
(Anode) and Tool is connected to negative
terminal (Cathode).
• Gap between tool and workpiece is usually
maintained between 0.075 to 0.125mm at
the start of the cycle. It increases by the
amount of stock removal per cycle upto
0.50mm.
• Electrolyte is passed between tool and
workpiece through several rows of small
holes in the tool body.

63. • Electrolyte is supplied about 122 lit/min
under the pressure of upto 1.05 N/mm2
depending upon the workpiece size.
• Bonded abrasive honing stones are inserted
in slots in the tool and these stones are
fed out with equal pressure in all direction,
So that cutting faces are in constant contact
with the cylinder surface.
• Its suitable for internal cylindrical grinding
with a size tolerance of 0.012mm on the
diameter.

65. ADVANTAGES
• MRR is faster with reduced tool wear, its
about 10 times faster than conventional
honing and 4times faster than internal
grinding.
• Burr free stress free components are
produced.
• Less pressure is required between honing
stones and workpiece.
• Noise and distortion are reduced when
honing thin walled tubes.

66. • Cylinder Bore Honing - Engine Building Video
- Hone Piston Wall
• https://www.youtube.com/watch?v=HQfh6AZ
xL08
• Electrochemical Honing of helical Gears
• https://www.youtube.com/watch?v=qaECkm
w4vqY