Download 39146132-Electrochemical-Machining-ECM

Electrochemical
Machining (ECM)
Dr. Lotfi K. Gaafar
13/05/2002
AUC - MENG
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Electrochemical Machining
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AUC - MENG
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Electrochemical Machining
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
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Electrochemical Machining
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Operating Principle
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As the tool approaches
the work piece it erodes
the negative shape of it.
Thus complex shapes are
made from soft copper
metal and used to
produce negative
duplicates of it. This
process is called
electrochemical sinking
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Operating Principle
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The tool may also be connected to a CNC machine to
produce even more complex shapes with a single tool.
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Operating Principle
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Several tools may be joined to provide a fast
broaching technique on hardened material.
Conventional machines may be easily changed to
an ECM and is a common practice.
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Main Subsystems
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The power supply.
The electrolyte circulation system.
The control system.
The machine.
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ECM Components
(Power)
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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.
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ECM Components
(electrolyte circulation system)
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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.
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ECM Components
(control system)
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Control parameters include:
Voltage
 Inlet and outlet pressure of electrolyte
 Temperature of electrolyte.
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The current is dependant on the above
parameters and the feed rate.
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ECM Components
(Machine)
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The machine is a major subsystem of the ECM.
It includes the table, the frame, work enclosure
(prevents the electrolyte from spilling), the work
head (where the tool is mounted)
The tools (electrodes) are also part of the
machine system
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Advantages
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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.
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Advantages over EDM
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Faster than EDM
No tool wear at all.
No heat affected zone.
Better finish and accuracy.
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Disadvantages
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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.
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Applications
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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.
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Economics
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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.
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Products
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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:
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Stress free grooves.
Any groove geometry.
Any conductive metal can be machined.
Repeatable accuracy of 0.0005”.
High surface finish.
Fast cycle time.
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Safety Considerations
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Several sensors are used to control short circuit,
turbulence, passivation, contact and overcurrent
sensors. In case of contact, immense heat would
be generated melting the tool, evaporating the
electrolyte and cause a fire.
The worker must be insulated to prevent
electrocution.
The tool and the work piece must be grounded
before any handling is performed.
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Safety Consideration
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Hydrogen gas emitted is very flammable, so it
should be disposed of properly and fire
precautions should be taken.
The waste material is very dangerous and
environmentally unfriendly (metal sludge) so it
must be recycle or disposed of properly.
Electrolyte is highly pressurized and worker
must check for minor cracks in piping before
operating.
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Pulsed Electrochemical
Machining
A form of electrochemical machining; the current
is pulsed to eliminate the need for high
electrolyte flow
Improves fatigue life of the part
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Electrochemical Grinding
Uses a rotating cathode embedded with abrasive
particles for applications comparable to milling,
grinding and sawing
Most of the metal removal is done by the
electrolyte, resulting in very low tool wear
Adaptable for honing
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Electrochemical Grinding
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