2. INTRODUCTION
• ECM is one of the recent and most useful machining process.
• In this process, electrolysis method is used to remove the metal from
the workpiece.
• It is best suited for the metals and alloys which are difficult to be
machined by mechanical machining process.
•This machining process is based Michael Faraday’s classical laws of
electrolysis, requiring basically twoelectrodes, an electrolyte, a gap and a
source of D.Cpower of sufficient capacity.
3. What is ECM ?
• Electrochemical machining (ECM) is a method of removing metal
particules by an electrochemical process instead of standard machining
methods.
• It gives a new perspective to machining process and being an initiator
of new tecnologies.
4. Elements of ECM
Important elements of ECM are:
1. Electrolyte
2. Tool (cathode)
3. Work-piece (anode)
4. D.C power supply
Electrolyte:
Common electrolytes used are sodium chloride, sodium nitrate,
sodium hydroxide, sodium fluoride, sodium chlorate, potassium
chloride and sulphuric acid.
These solution on reaction produce an insoluble compound in the form
of sludge.
5. The essential characteristics of electrolyte includes:
1. Good electrical conductivity.
2. Non-toxicity and chemical stability.
3. Non-corrosive property.
4. Low viscosity and high specific heat.
High velocity flow over the electrode surface is one of the key factors
of ECM. It is necessary to prevent crowding of hydrogen gas and debris
of machining.
The main functions of an electrolyte in ECM are:
1. It carries the current between tool and work-piece.
2. It removes the products of machining and other insoluble products
from the cutting region.
3. It dissipates heat produced in the operation.
6. Tool (cathode):
The most commonly used tool material are copper, brass, titanium,
copper tungsten and stainless steels when electrolyte is made of salts of
sodium and potassium.
The other tool materials are aluminium, graphite, bronze, platinum and
tungsten carbide.
The general requirements of tool material in ECM are:
1. It should be conductor of electricity.
2. It should be rigid enough to take up the load due to fluid pressure.
3. It should be chemically inert to the electrolyte.
4. It should be easily machinable to make it in the desired shape.
7. Work-piece (anode):
Work-piece should be conductor of electricity. So it is almost limited
to metals only.
Power Supply:
1.Type: direct current
2.Voltage: 2 to 35 V
3.Current: 50 to 40,000 A
4.Current density: 20 A/cm2 to 300 A/cm2
8. Electrolysis process
•In the electrolytic circuit the electron is flow from the work-piece
through the power supply to the tool.
•The electrolysis process that takes place at the cathode liberates
hydroxyl ions(OH-) and free hydrogen.
•The hydroxyl ions combine with the metal ions of the anode to form
insoluble metal hydroxides and material is thus removed from the anode.
• At cathode, the following reactions takes place:
1. M++ e- M(M denotes metal)
2. 2H++ 2e- H2(Hydrogen evolution)
9.
10. •At anode, the following reactions takes place with a halogen electrolyte:
1. M + e- (Metal dissolution)
2. 2H2O+4H+ 4e- (Oxygen evolution)
•As an example, in machining of iron in NaCl electrolyte, at the cathode
the reaction products are FeCl2, Fe(OH)2, Fe(OH)3 which forms a layer
and this is how iron is removed by electrolytic action.
•Current of 1000 A would dissolve iron at the rate of about 15 g/min and
generate hydrogen at a rate of about 300 cm3/min.
3.FeCl2+2(OH)-=Fe(OH)2+2Cl-
12. Working of ECM
In the actual process of ECM, the cathode is tool shaped(mirror image
of work-piece) and anode is the work-piece.
A gap(0.05 to 0.7 mm) is provided between the tool and work-piece and
electrolyte flows through the gap at a velocity of 30 to 60 m/s and it
completes the electrical circuit.
Electrolyte is pumped at high pressure of 20 kgf/cm2(1.96 MPa)
through the gap.
Electrolyte must be circulated at a rate sufficiently high to conduct
current between them and to carry heat.
13. The electric current is of the order of 50 to 40,000 A at 5 to 35 V D.C
for current density of 20 to 300 A/cm^2.
Power of 3 KWh is needed to remove 16 cm3 of metal which is almost
30 times the energy required in the conventional process(when the
material is readily machinable).
14. Process Parameters
• Power Supply Type -direct current
• Voltage -2 to 35 V
• Current -50 to 40,000 A
• Current density -0.1 A/mm2 to 5 A/mm2
• Electrolyte Material -NaCl and NaNO3
• Flow rate - 20 lpm per 100 A current
• Pressure -0.5 to 20 bar
• Dilution -100 g/l to 500 g/l
• Working gap -0.1 mm to 2 mm
• Overcut -0.2 mm to 3 mm
• Feed rate -0.5 mm/min to 15 mm/min
• Electrode material -Copper, brass, bronze
• Surface roughness-Ra 0.2 to 1.5 μm
15. 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 commonly used on thin walled, easily deformable and brittle material because
they would probably develop cracks with conventional machining.
It is used in machining of hard-heat-resisting alloys.
It is used in cutting cavities and holes in various products, machining of complex
external shapes like that of turbine blades, aerospace components and
machining of tungsten carbide and nozzles of alloy steels.
Any conducting material can be machined by this method.
16. Advantages
There is no cutting forces therefore clamping is not required except for controlled
motion of the work piece.
It can machine configurations which is beyond the capability of conventional
machining processes.
Very accurate (tolerance of ±0.02 mm).
Relatively fast.
Can machine harder metals than the tool.
Extremely thin materials can be easily worked without distortion.
Tool wear is nearly absent.
Better surface finish (0.2 to 0.8 micron).
17. Disadvantages
High energy consumption.
Non conducting material cannot be machined.
Corrosion and rust of ECM machine can be hazardous but preventive
measures can help in this regard.
