3. Principle of Electrochemical Machining (ECM)
In ECM workpiece forms the anode, and a properly
insulated tool having shape similar to that desired in
the workpiece forms the cathode part of the
electrical circuit.
The tool and the workpiece are positioned closer to
each other with a conductive electrolyte flowing
through a small gap between the workpiece and the
tool
3
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4. Cont…
When the current is passed, dissolution of the
workpiece occurs.
The chemical properties of the electrolyte are such
that, the constituents of the workpiece material
dissolve into the solution during electrolysis, but do
not plate on the tool.
The shape obtained in the workpiece material is
exactly similar to the shaped tool.
4
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5. Cont…
Uses an electrolyte and electrical current to ionize
and remove metal atoms
Can machine complex cavities in high-strength
materials
Leaves a burr-free surface
Not affected by the strength, hardness or toughness
of the material
5
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7. Elements of ECM Process
The elements of ECM process include:
• Cathode tool, shape similar to the desired in the w/p
• Anode workpiece which is a good conductor of
electricity
• DC Power supply of sufficient capacity so that high
current density can be maintained b/t tool and
workpiece
• Electrolyte , a liquid that carries electric current and
also acts to complete the circuit between the tool and
workpiece metal
7
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8. Need for ECM
• Hard and complicated shape cannot be easily
machined by conventional methods.
• Some of the NTM are not suitable for mass
production
8
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9. ECM Equipment
• ECM is special purpose machine, it is tool oriented
Followings are the important equipments of ECM
1. Tool
2 .Electrolyte
3. Filters
4. Source of Power
9
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10. Tool
• Tool forms the negative terminal ( cathode)
• Shape of the tool must be similar to the shape desired
in the workpiece
• Tool should be smaller than the required dimension
• The difference in tool size and required size is
known as overcut
• The tool material should be
• Easy to machine,
• Good stiffness to resist high stiffness,
• Resist to chemical reaction of the electrolyte
• Good thermal and electrical conductor 10
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11. Cont…
• Tool should be insulated to prevent machining action
on its side by the electrolyte as it flows around the
tool .
• The insulator is usually applied to the tool by
spraying or dipping process.
• Insulator must remain firmly fixed to the tool while
resisting the turbulent flow of the electrolyte, its heat
and abrasive action.
• Porcelain, vinyl, phenolic enamel, teflon and epoxy
etc are the insulting materials
Too Materials: Bronze, copper, stainless steel ,
reinforced plastic, titanium 11
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12. Electrolyte
Functions of Electrolyte
• Complete the electric circuit between the tool and
workpiece
• Act as a conductor to carry current
• Remove the products of electrochemical reaction
from the gap between the tool work interface.
• Carry the heat generated from the machining zone
Eg: sodium chloride, Potassium chloride, sodium
nitrate and sodium chlorate etc…
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13. Cont…
Characteristics of Electrolyte
• High electrical conductivity
• Low viscosity
• High specific heat
• Chemical stability
• Resistance to formation of passivating film on the
work surface
• Non corrosive and non toxic
• Inexpensive and easily available
13
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14. Cont…
Sl.
No
Electrolyte Workpiece materials
1 Sodium Chloride (NaCl)
Potassium Chloride (KCl)
Sodium nitrate (NaNO3)
Steel, iron bases alloys
and steel alloys with
nickel and cobalt base
2 Sodium Chloride (NaCl)
Potassium Chloride (KCl)
Sodium Hydroxide (NaOH )
Aluminum and
aluminum alloys,
copper and copper
based alloys
3 Sodium Chloride (NaCl)
Sodium nitrate (NaNO3)
Gray cast iron
4 Sodium Chloride (NaCl)
Potassium Chloride (KCl)
Titanium alloys
14
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15. Filters
15
• Filters are placed in the system to clean the
contamination electrolyte
• A wire mesh filter of 75µm size made from monel
metal are used
• Periodically mesh need to clean to avoid clogging of
chips
• Some time centrifugal separator can be used
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16. Power supply
16
• The power needed to operate the ECM is obviously
electrical.
• The current density must be high.
• The voltage must below to avoid a short circuit.
• The electric current is of the order of 50 to 40000
Ampere at 5 to 30 V D.C. for a current density of 20
to 300 Ampere/Square cm, across a gap of 0.05 to
0.70 mm between the tool and the work piece.
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19. Cont…
19
• The tool should have shape similar to the desired in the
workpiece is fed towards workpiece maintaining a small
gap of 0.25 mm
• The tool movement is controlled by servo drive
• A high current low voltage DC power supply is
connected between the tool and workpiece
• The tool is connected to negative terminal ( cathode)
• Workpiece is connected to positive terminal (anode)
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20. Cont…
20
• The electrolyte is pumped at a high pressure through the
small gap between the tool and the workpiece, thus
providing the necessary path for electrolysis.
• When the current is passed, dissolution of the
workpiece occurs
• Flowing electrolyte washes the metal ions away from
the workpiece before they have a chance to plate onto
the tool
• As the tool moves downwards to maintain a constant
gap, the workpiece is machined to the same shape as
that of the tool.
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22. Cont…
• During ECM, there will be reactions occurring at the
electrodes i.e. at the anode or work piece and at the
cathode or the tool along with within the electrolyte.
• For electrochemical machining of steel, generally a
neutral salt solution of sodium chloride (NaCl) is
taken as the electrolyte.
• The electrolyte and water undergoes ionic
dissociation as potential difference is applied
22
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23. Cont…
NaCl ↔ Na+ + Cl-
H2O ↔ H+ + (OH)-
As the potential difference is applied between the work
piece (anode) and the tool (cathode), the positive ions
move towards the tool and negative ions move
towards the work piece.
Thus the hydrogen ions will take away electrons from
the cathode (tool) and from hydrogen gas as
2H+ + 2e- = H2 ↑ at cathode
23
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24. Cont…
Similarly, the iron atoms will come out of the anode
(work piece) as: Fe = Fe++ + 2e-
Within the electrolyte iron ions would combine with
chloride ions to form iron chloride and similarly
sodium ions would combine with hydroxyl ions to
form sodium hydroxide
Na+ + OH- = NaOH
In practice FeCl 2 and Fe(OH) 2 would form and get
precipitated in the form of sludge.
24
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25. Cont…
In this manner it can be noted that the work piece
gets gradually machined and gets precipitated as
the sludge.
Moreover there is not coating on the tool, only
hydrogen gas evolves at the tool or cathode.
As the material removal takes place due to atomic
level dissociation, the machined surface is of
excellent surface finish and stress free.
25
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26. Cont…
Cathode Reaction
Na+ + e- = Na
Na+H20 = Na(OH)+H+
2H++2e- =H2 ↑
It shows that there is no deposition on tool but only gas
is formed, whereas, in cathode in machining an iron.
26
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28. Process Parameters
• Current density
• Tool feed rate
• Gap between workpiece and tool
• Velocity of electrolyte flow
• Type of electrolyte, its concentration and
temperature
28
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29. Current density
• Current density is the current that can be passed into
a square inch of work area.
• The electric current is of the order of 50 to 40000
Ampere at 5 to 30 V D.C. for a current density of 20
to 300 Ampere/Square cm, across a gap of 0.05 to
0.70 mm between the tool and the work piece
• At low current densities MRR is small
• The current density must be high.
• The gap between the tool and the work piece must
be low for higher accuracy. 29
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31. Tool feed rate
• Tool feed rate is directly proportional to current
density
• If the feed rate is increased, the electrical resistance
of the tool work gap reduces to allow more current
to flow resulting in high MRR and surface finish
will increases
31
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32. Gap between workpiece and tool
• The tool and workpiece are positioned as close
together to encourage efficient electrical
transmission.
• Small gap results in high current densities hence
high MRR
• The gap size varies from 0.25 – 0.76 mm
• Optimized gap size is 0.25mm
32
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33. Velocity of electrolyte flow
• Optimum flow velocity of electrolyte flow is 15 –
16 m/sec.
• If electrolyte flow is too low, the heat and by
products of electrolytic reaction, build in the gap
causes non uniform metal removal.
• Too high velocity causes cavitations, this also
leads non uniform metal removal
33
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34. Type of electrolyte, its concentration and
temperature
• Type of electrolyte selected is depends on the tool
and the workpiece material.
• Sodium chloride is cheap and have good
conductivity.
• NaCl is corrosive it is not suitable for tungsten
carbide , molybdenum materials.
34
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35. Cont…
• Sodium nitrate is also have good conductivity and
less corrosive in nature.
• Sodium Nitrate does not produce a good surface
finish as that of NaCl.
• Sodium Nitrate is costlier and it is suitable for
machining aluminum and copper.
35
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36. Cont…
• The electrolyte concentration with water affect the
surface finish.
• Low concentration decreases the equilibrium
machining gap , it leads to better surface finish
and good tolerance control.
• Electrolyte temperature seriously affects the
overcut
36
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37. Cont…
• The power loss in the electrolytic reaction gives
rise to an increase in the temperature of the
electrolyte.
• This heat must be carried away from the cutting
area to maintain stable and study condition.
• Low temperature of electrolyte is conductive to
better surface finish and tolerance.
37
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38. ECM Tooling Techniques
• The tool used in ECM process is approximately the
mirror image of the shape to be machined in the
workpiece.
• Hence the tool is properly designed in size and
shape
38
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44. Electrolyte Flow
• Proper electrolyte circulation is essential for
accurate machining in ECM process.
•
• The tool must be properly designed to permit a
uniform electrolyte flow in all machining areas.
• Insufficient or excessive flows produce
undesirable effects during machining
44
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45. 1. Divergent flow
• Electrolyte flows from the inside of the tool
• Then Around the cutting edges and up through the
machined hole.
• This method is simple, inexpensive
45
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46. 2. Convergent flow
• The electrolyte is admitted through a chamber
pressurize the area outside the work and tool
• Through the valve fluid flow can be controlled
46
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47. Advantages of ECM
• There is no cutting forces therefore clamping is
not required except for controlled motion of the
work piece.
• There is no heat affected zone.
• Very accurate.
• Relatively fast
• Can machine harder metals than the tool.
47
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48. Disadvantages
• More expensive than conventional machining.
• Need more area for installation.
• Electrolytes may destroy the equipment.
• Not environmentally friendly (sludge and other
waste)
• High energy consumption.
• Material has to be electrically conductive.
48
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49. Applications
• The most common application of ECM is high
accuracy duplication. Because there is no tool
wear, it can be used repeatedly with a high degree
of accuracy.
• It is also used to make cavities and holes in
various products.
• It is commonly used on thin walled, easily
deformable and brittle material because they
would probably develop cracks with conventional
machining.
49
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50. Economics
• The process is economical when a large number of
complex identical products need to be made (at least
50 units)
• Several tools could be connected to a cassette to make
many cavities simultaneously. (i.e. cylinder cavities in
engines)
• Large cavities are more economical on ECM
50
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51. Products
• The two most common products of ECM are
turbine/compressor blades and rifle barrels. Each of
those parts require machining of extremely hard
metals with certain mechanical specifications that
would be really difficult to perform on conventional
machines.
• Some of these mechanical characteristics achieved by
ECM are:
– Stress free grooves.
– Any groove geometry.
– Any conductive metal can be machined.
– Repeatable accuracy of 0.0005”.
– High surface finish.
– Fast cycle time.
51
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52. Electro Chemical Grinding (ECG)
• ECG also known as Electrolytic grinding
• In ECG material removal of the electrically
conductive work material takes place through the
combined effect of electrochemical process and
mechanical action of the abrasive particles on the
work material.
52
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55. Cont…
• The process makes use of a metallic grinding wheel
which is embedded with insulating abrasive particle
such as aluminum oxide or diamond, set in a
conducting binding material.
• The grinding wheel acts as a cathode, while
workpiece acts an anode.
• The electrolyte usually sodium nitrate in water is
supplied through a nozzle on to the grinding wheel
near workpiece.
• Wheel carries it through the cutting process thereby
resulting an electrochemical action.
55
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56. Cont…
• Contact wire brushes are used on the spindle of the
grinder to supply current into the spindle from
which it then flow to the grinding wheel.
• When a DC voltage of about 5-15 V is applied
between the workpiece and the grinding wheel
• Suitable current densities are created, removing
material from the work surface by electro chemical
action coupled with abrasive action of the grinding
wheel.
56
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57. Cont…
• 10% volume of the work material is removed by
abrasive action and 90% by electrochemical action.
• The workpiece metal goes into solution as metal ions
( anodic dissolution) and bubbles of hydrogen are
generated at the wheel.
57
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58. Cont…
• Inorganic salts ( sodium/ Potassium salts)
• For ferrous, nickel and cobalt alloys – Nacl
• For copper silver – Sodium Nitrite
• KoH is less corrosive , cost is more
58
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59. Types of grinding wheels
• Grinding wheels are made of abrasive materials
and bonding agent.
1. Diamond wheel
For carbide tool/ materials/ HSS whose HRC > 65
Bonding agent – copper alloys
2. Non diamond face wheel
For Steel and steel alloys
Bonding agent - Aluminum oxide with brass
59
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60. Advantages
• Ability to grind any electrically conductive
material regardless of hardness.
• MRR are 5 to 10 times greater than Broaching,
milling or conventional m/cing
• Frequent grinding dressing is unnecessary.
• Long wheel life and low cost
• Accuracy and surface finish are comparable
• High production rates are possible
• No distortion of thin and fragile part
• No heat affected zone
60
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61. Disadvantages
• Workpiece must be electrically conductive
• High equipment cost
• Not suitable for graining low hardness metals
• Post cleaning of work and equipment parts is
necessary in order to avoid corrosion effects of
the electrolytes used
61
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62. Cont…
• The space b/t the grinding wheel and workpiece
must be filled with electrolyte at all times during
ECG otherwise it effects on MRR
• Sharp corners are difficult to obtain
62
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63. Electro Chemical Honing (ECH)
In Electrochemical honing material from electrically
conducting workpiece is removed by the
combined effect of anodic dissolution of work
metal and mechanical abrasion action.
63
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65. Cont…
• The process makes use of a hollow stainless steel
tool that acts as a cathode
• Workpiece acts a anode
• The tool is rotated and reciprocated on a rigid
spindle for precise metal removal from internal
cylindrical hole of the workpiece.
• Bonded abrasive stones protrude/ extend from at
least three locations around the circumference of
the tool
65
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66. Cont…
• The length of the honing stone is about half the
length of the bore to be honed.
• The stones are non conductive
66
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67. Advantages of ECH
• Ability to grind any electrically conductive
material regardless of hardness
• Burr free action
• Surface finish and accuracy are far comparable to
conventional honing
• Reduced noise and distortion
• High production rates are possible
• Stress free ( less conventional m/cing)
67
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68. Disadvantages of ECH
• Workpiece must be electrically conductive
• High equipment cost
• Post cleaning of work and equipment parts is
necessary in order to avoid corrosion effects of the
electrolytes used
68
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69. Chemical Machining (CHM/CM)
• Chemical Machining is a process used to remove
material by dissolution in a controlled manner,
from the workpiece by application of acidic or
alkaline solution (i e etchant).
• The working principle of chemical machining is
based on chemical etching
• The part of the workpiece metal where material is
to be removed is brought into contact with a
strong corrosive chemical called etchant.
69
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70. Cont…
• The etchant reacts with the work material in the
area to be cut and causes the solid work material
to be dissolved.
• Metal is removed by chemical attack of etchant
• The portion of the work material where material
is not to be removed is protected from chemical
attack by means of special coating called
maskants.
70
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71. Maskants (chemically resistant coatings):-
• Used to cover the surfaces which are not to be
machined.
• Maskants are the materials which do not allow
etchants to penetrate through, to reach the work
material to dissolve.
71
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72. Need for CHM
• Chemical Machining technique is quite useful for
producing complex configurations in delicate
parts, otherwise would get damaged by the
application of forces in case of the conventional
machining processes.
• This process is used in many industries, like
aviation industries for making aircraft wing
panels, printed circuit boards (PCB), jewelry, etc.
72
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73. Elements Of Chemical Machining Process
1. Etchants
2. Resists or Maskants
73
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74. 1. Etchants
• Etchants are acid or alkaline solutions maintained
within a controlled composition and temperature
• The workpiece materials to be removed is
sprayed or immersed in a suitable etchant.
• The etchant reacts with the work material in the
area to be cut and causes the solid work material
to be dissolved in it.
74
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75. Selection of etchant
• Type of workpiece metal that is being etched
• Depth of etch required
• Rate of metal removal
• Surface finish required
• Type of maskant used
• Un harmful to human operator
• Ability to regenerate the etchant solution, readily
neutralize, dispose of its waste product
• Availability and low cost
75
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76. Etchant Characteristics
Sl No Work Material Chemical
Etchant
Etching
Temperature °C
Etch rate
(mm/min
1 Aluminum
& Alloys
FeCl3 49 0.013-
0.025
2 Copper &
Alloy
FeCl3
CuCl2
49
54
2
1
3 Steel FeCl3 54 0.025
4 Nickel FeCl3 49 0.13-0.38
5 Magnesiu
m
HNO3 32-49 1
6 Titanium HF -
7 Glass HF /
HF +
HNO3
-
76
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77. 2. Resists or Maskants
• Maskants are polymer or rubber based materials,
used to protect portion of the workpiece material
where chemical dissolution action is not needed.
• The maskant can be applied on the work material
by various methods like dip, brush, spray, roller,
electro coating and adhesive tapes.
• Multiple coats of maskant are frequently used to
increse the etchant resistance and avoid the
formation of pinholeson the machined surface
77
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78. Selection of Maskants
• Chemical resistance required
• Be inert to the chemical reagent used
• Be tough enough to witstand handling
• Adhere well to the workpiece surface
• Allow itself to be scribed easily
• Be removed easily and inexpensively after etching
• Be able to withstand the heat generated by etching
• Availability and low cost
78
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79. Etchant Characteristics
Sl No Work Material Maskant Material
1 Aluminum &
Alloys
Polymer, Butyl rubber and
neoprene
2 Copper &
Alloy
Polymer
3 Iron based
alloys
Polymer, poly vinyl
chloride, polyetilien butyl
rubber
4 Nickel Neoprene
5 Magnesium Polymer
6 Titanium Polymer
79
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80. Chemical Blanking Process
• Chemical blanking is a process of producing a
part from thin sheet metal by chemically etching
the periphery of the desired shape.
• The material removed by chemical dissolution
Application of CBP
- Burr free etching of pcb
- decorative panels
- Thin sheet metal stamping
80
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81. Process
• Step 1 Workpiece pre cleaning process
• Step 2 Masking
• Step 3 Etching
• Step 4 De masking
81
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82. Cont…
Workpiece pre cleaning process:
• Pre cleaning is of utmost importance in order
to remove oil, grease, dirt, rust or any foreign
substance for the work surface so as to produce
a good adhesion of the masking material
82
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83. Cont…
Masking :
Masking involves covering the portions of the
workpiece metal where material is not to be
removed by the chemical action of the etchant.
Suitable maskant like polymer, rubber or any other
materials based on the w/p material.
Method : dip, brush, spray, roller, electro coating etc
83
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84. Cont…
Etching :
Removal of metal from the w/p takes place by
etching process.
The workpiece materials to be removed is sprayed or
immersed in a suitable etchant.
The etchant reacts with the work material in the area
to be cut and causes the solid work material to be
dissolved in it.
84
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86. Cont…
De Masking :
• When etching is completed, the mask is removed
either through mechanical or chemical means
• Any etchant on the material is also removed with
a wash or clear, cold water
• A deoxidizing bath may also be required in order
to remove the oxide films left on the surface of
the work material
86
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87. Chemical Milling / Contour Machining
• Chemical milling is a process used to produce
shapes by chemically etching selective portion of
material from relatively large surface area of work
metal.
• The main purpose is to produce shallow cavities
with complex profiles on plates, sheets, forgings
generally for the overall reduction of weight
87
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88. Process
• Step 1 Workpiece pre cleaning process
• Step 2 Masking
• Step 3 Etching
• Step 4 De masking
88
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91. Cut and peel method
In this method , the maskant is initially applied on a
large surface area and then scribed or cut with a
sharp knife followed by careful peeling of the
mask from the selected areas to be etched
This method is used for those applications where
thick maskants are laid on work surface due to
the necessity for withstanding high exposure to
the etchant for extended periods.
91
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92. Cont…
Since scribing the maskant is done with a knife, this
method of maskant is used where accuracy of the
surface generated is not a critical factor
92
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93. Photographic Resist Method
In this method the mask is applied on the work
surface using photographic techniques.
The masking material contains photosensitive
chemicals, which are exposed to light through a
negative image of areas to be etched.
These area are then removed using photographic
developing techniques, while the remaining
areas are exposed for etching.
93
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94. Cont…
This method is suitable for small parts and mass
production
Fabrication of integrated circuits and pcbs
94
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95. Screen resist method
Screen resists are materials that can be used on the
w/p through normal silk screening techniques.
The maskant is pained through a silk or stainless
steel mesh, which has areas blocked off to allow
selective passage for maskant.
The blocked pattern corresponds to the image that is
etched.
95
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96. Cont…
The screen is pressed against the work surface and
maskant is rolled on.
When the screen is removed, the maskant remains
on the part in the desired pattern.
The image accuracy is better than that achieved by
other methods
96
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97. Process Characteristics of CHM
• - Type of etchan, Concentration of etchant,
Operating temperature and circulation, Type of
maskant and its application method
Affect on the MRR, Accuracy, Surface finish
97
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98. Advantage
• Suitable for mass production
• No burr are formed
• No stress induced
• Low capital investment
• Design changes can be implemented quickly
• Less skilled operator
• Good surface finish
98
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99. Disadvantage
• Limited depth of cut
• Difficult to produce sharp radius
• Handling and disposal of chemical is difficult
• Hydrogen absorption leads to brittlness
• Inter granular attack on some materials changes
the structure
• Homogeneity of the material will change
99
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100. Applications
• Shallow cuts in large thin sheets for weight
reduction in pre formed aerospace components
100
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