Electrochemical Machining

Prepared by
M.USHA RANI
Assistant Professor of M.E
SRIT.
Introduction
 Non-conventional machining system in which
metal is removed by electrochemical process.

 Characterized as ‘Reverse Electroplating’ means it

removes metal instead of adding it.

Normally used for mass production and for hard

materials that are difficult to machine using
conventional processes.

Both external and internal geometries can be

Machined.
Concept
 Metal removal is achieved by electrochemical dissolution of an anodically
polarized workpiece which is one part of an electrolytic cell in ECM.

 when an electric current is passed between two conductors dipped into a

liquid solution named as Electrolysis .

 Electrolytes are different from metallic conductors of electricity in that the

current is carried not by electrons but by atoms, or group of atoms, which
have either lost or gained electrons, thus acquiring either positive or
negative charges. Such atoms are called ions.
Electrolytic dissolution of iron.
Principle
Faraday’s law of electrolysis :
The Weight of the substance produced during
electrolysis process is directly proportional to
1.The current which passes
2.The length of time of process
3.The equivalent weight of the material
Two dissimilar metals are in contact with an
electrolyte and anode loses metal to cathode.
Working Principle
Continue..
 the workpiece and tool are the anode and cathode, respectively, of
an electrolytic cell, and a constant potential difference, usually at
about 10 V, is applied across them.

 A suitable electrolyte, for example, aqueous sodium chloride (table

salt) solution, is chosen so that the cathode shape remains
unchanged during electrolysis.
 The electrolyte is also pumped at a rate 3 to 30 meter/second,
through the gap between the electrodes to remove the products of
machining and to diminish unwanted effects, such as those that
arise with cathodic gas generation and electrical heating.
 The rate at which metal is then removed from the anode is
approximately in inverse proportion to the distance between the
electrodes
Schematic diagram
ECM Components (Power)
 The power needed to operate the ECM is obviously electrical. There
are many specifications to this power.
 The current density must be high.
 The gap between the tool and the work piece must be low for higher
accuracy, thus the voltage must be low to avoid a short circuit.
 The control system uses some of this electrical power.
ECM Components
(electrolyte circulation system)

 The electrolyte must be injected in the gap at high speed (between

1500 to 3000 m/min).

 The inlet pressure must be between 0.15-3 MPa.

 The electrolyte system must include a fairly strong pump.

 System also includes a filter, sludge removal system, and treatment

units.

 The electrolyte is stored in a tank.

ECM Components (control system)

 Control parameters include:

 Voltage
 Inlet and outlet pressure of electrolyte
 Temperature of electrolyte.

 The current is dependant on the above parameters and the feed

rate.
Advantages
 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
 Faster than EDM
 No tool wear at all.
 No heat affected zone.
 Better finish and accuracy.
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.
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.

 Sinking operations (RAM ECM) are also used as an alternative to RAM

EDM.

 It is commonly used on thin walled, easily deformable and brittle

material because they would probably develop cracks with
conventional machining.
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 and can be processed

in 1/10 the time of EDM.
ELECTROCHEMICAL GRINDING
 Concept
 The main feature of electrochemical grinding (ECG) is the use of a
grinding wheel in which an insulating abrasive, such as diamond
particles, is set in a conducting material. This wheel becomes the
cathode tool .
 The non conducting particles act as a spacer between the wheel and
workpiece, providing a constant inter electrode gap, through which
electrolyte is flushed.
 Accuracies achieved by ECG are usually about 0.125 millimeter
 A wide application of electrochemical grinding is the production of
tungsten carbide cutting tools. ECG is also useful in the grinding of
fragile parts such as hypodermic needles
Concept
 Combines electrochemical machining with conventional grinding.

 The equipment used is similar to conventional grinder except that the

wheel is a rotating cathode with abrasive particles.

 The wheel is metal bonded with diamond or Al oxide abrasives.

 Abrasives serve as insulator between wheel and work piece. A flow of

electrolyte (sodium nitrate) is provided for electrochemical machining.

 Suitable in grinding very hard materials where wheel wear can be very
high in traditional grinding
Sample ECMed parts
Chemical machining
Local melting of material by suitable diluent.

 Machining of metal materials,

 Removing speed of material independence on
hardness and on toughness,
 Surfaces with complicated shape with high
accuracy and quality,
 Here is no originated heat and mechanical
influence area,
 Large areas – more economical than milling
Chemical machining
1 – base material,
2 – mask,
3 – holes carved out of
mask,

In the place of holes the

material is melted by
influence of diluents.
Material machinability
Four groups of materials by chemical machinability:

 Copper, bronze – easy they are melted, good

machinability by chemical machining,
 nickel, zinc, aluminium
 manganese, molybdenum,
 chrome, gold, wolfram – they are hard melted,
bad machinability by chemical machining
Diluents for chemical machining

 Ferrous metals – different acids,

 copper, alloys of copper, heavy metals –

chloride of ferrum FeCl3,

 Aluminium, alloys of aluminium, light metals –

caustic soda NaOH
Workpiece preparation for
chemical machining
 Grease removal and surface cleaning –
removing the allochemicals from surface and
oxidic coats too (Al alloys – AL2O3 coat), dipping
into 5% medium NaOH and next into 30%
medium of acid of nitride,
 steeping – increasing of mask adhesion, dipping
into medium H2SO4
 masking – coating resisted on influence of
diluent (resin, enamel) thickness till 2 mm.
Workpiece preparation for
chemical machining
 Mask drying – mask coating is drying 6 to
8 hours, it can be accelerated in the furnace
(small workpieces),

 Engraving of mask – into drying mask are

created holes (hand engraving, engraving
by laser ...),
Time needed for machining

 It is independence on the size of the machined

surface,

 It is depend on depth of machining only,

 Speed of outline 0.01 till 0.5 mm/min.,

 mask resisted to outlining approximately 8 hours.

Mask undercutting
Speed of outline in homogenne material is the
same in all directions. Rate of undercutting is
approximately the same as depth of outlining.
Mask undercutting
 Is not possible to make shape rims,
 In immersion into etching pool is needed to
assure that origin gas is not to mass in the place
of undercut (scaling of mask, non-constant speed
of undercutting....), side long immersion,
mixturing,
 Mixturing of etching pool:
 Washing off etching impurities,
 Asked concentration of etchant in the place of etching,
 Outflow of gas bubbles.
Spraying of etching solution
Kinds of chemical machining
 Chemical clipping,
 chemical milling (deeping),
 Chemical engraving
 chemical sharping,
 Chemical polishing,
 Machining by active substance,
 Photochemical machining,
 termic removing of burrs.
Chemical clipping
 Thin plates,
 Completely component is sinking,
 Small, shape difficult components

Example:
 Plotters of shavers
Chemical milling
Accuracy shaping of difficult big shape surfaces.
Speed of removing is moving round 0.025 mm/min.
Originated undercutting, is necessary to speculate
with undercutting in the mask production.
Dimensions accuracy is given by thickness of
removing layer. Roughness is between Ra=0,75
to Ra=3,8.
Chemical milling
Using of chemical milling:
 aerial and cosmic industry – local releasing
of casts and forgings of light and high
strength alloys,

 Small metal components of high strength

material when is not economical to produce
dies.
Chemical engraving, grinding,
polishing
 engraving – dimension of picturing is small for
using of mechanical engraving – matrixs of post
marks,

 grinding – very accurated shapes (accuracy

under 1mm), low roughness (Ra 0,01),

 polishing – still softer than grinding, using in

small and shape difficult components that by
mechanical kind is not possible to polish.
Machining by active substance
Machining shape difficult surfaces.
Semi-solid substance of cellulose (electro gel)
impregnated by acid is attach to the workpiece
surface. In the place of contact the workpiece is
melted.
Is possible to achieve step by step removing until
depth 10 mm. Dimension accuracy is from 0,02 to
0,07 mm.
For acceleration of process is possible to connected
electric voltage until 10V.
Machining by active substance
Photochemical machining
Mask is created by photographic kind.

Using in production:
 Masks of TV set and screening,
 Code disks,
 Optical divider,
 gasket,
 Ornamental object,
 Semiconductor components.
Photochemical machining
 Patern of production – laser beam creating
the sign in the photographical film. This picture
(master) is frequently applied to photo tool.
(patern).
 Preparation of surface – surface must be
cleaned, grease removing, eventually to pickle,
 Coating of photoresist – it is polymer sensitive
to ultraviolet emission is necessary to dry him.
 Processing of photoresist – through the
pattern is photoresist emissed by light of
suitable wave length (UV) and is created mask
(positive, negative).
Photochemical machining
Advantage of photochemical machining:

 Low costs of tools,

 Low costs of modification,
 Simply transmission to series production,
 Properties of the base material are not damages,
 No originated burrs.
Thermic removing of burrs
Burrs are removed by influence of thermic
wave (by explosion).
Thermic wave has temperature more than
3000°C and lasted particular s.
Burrs are melted or evaporated but workpiece
is not in time to absorbing a lot of heat.
Burrs are verily removed from inaccessible
places.
 UNIT III ESSAY QUESTIONS
1.Explain the fundamentals of electro machining and process of
metal removal.
2.Expain the electro chemical grinding process with neat sketch.
3.Describe the tooling, process variables and its applications in
electro chemical machining process.
4.Decribe the applications and economic aspects of ECM.
5.Describe the principle of metal removal, fundamentals of
chemical machining.
6.Describe the process variables, advantages of chemical
machining process.
7. Explain the applications and advantages of chemical machining
process.
8.Explain the description of equipment, process parameters of ECM
with neat sketch.