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P Saha IITKGP
Micro Electrodischarge Machining
also called
Micro-EDM
or
µ-EDM
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P Saha IITKGP
Scheme of EDM
Potential difference between
the two electrodes A series of sparks Intense heat
Melts and
evaporates the
materials
Dielectric fluid mech14.weebly.com
P Saha IITKGP
Attribute EDM µ-EDM
Feature size
(minimum)
500 micron 5 micron
Max. surface
roughness
2 micron 0.1 micron
The most common size for Micro-EDM
ranges from 20 µm to 250 µm.
EDM to Micro EDM
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Reduce the energy per pulse
Provision for making micro tools in-situ
Requirements: to Micro EDM
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Provision for making micro tools in-situ(i.e. making the EDM tool in the same set up)
What may happen if you do not make the
tool in-situ?
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P Saha IITKGP
Micro Electro-discharge grinding (µEDG) is a non-
contact process by which micro tools are
manufactured by machining the rotating work piece
(commercially available tool mounted on the spindle) :
3 ways:
(i) against a sacrificial block, or
(ii) against a rotating sacrificial disk, or
(iii) by Wire Electro-Discharge Grinding (WEDG).
Micro-tools Manufacturing by Micro-EDG
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P Saha IITKGP
(a) Stationary
sacrificial block as tool
Electric
discharge
Collet
Micro-tool
(getting
fabricated)
Limitations
Maintaining parallelism between the axis of the tool and interacting face
of the sacrificial block may be difficult results in non-uniform gap
along length of the tool
Dimensional control of gap between rod and the block/disk is problematic
due to continuous wear of the block and debris build-up.
(b) Rotating sacrificial
disk as tool
Electric
discharge
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(c) by Wire Electro-Discharge Grinding (WEDG)
A fresh cathode surface (traveling wire) is
exposed for each discharge job (micro
tool-in-making) can be advanced towards
the wire in steps by an amount decided by
its desired diameter (amount of reduction
needed).
Wire travel
Spindle rotation
Z-movement
Electrode diameter down to 5 µm is possible. This may be used for
producing micro holes or other shapes in thin electrically conductive
materials.
(c) Guided running wire as tool
Electric
discharge
Collet
Micro-tool
(getting
fabricated)
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Schematic of a full Set Up
(In-situ Micro tool making by Wire Electro Discharge Grinding (WEDG)
Uses WEDG for electrode preparation with a wire of 200 µm diameter
Deionised water is used as dielectric
Water jet is applied at machining point using fine injection needle
Deep micro-holes with an aspect ratio around 10 can be machined
In-situ
Micro tool
WEDG
Job for
Micro Hole
Drilling)
All
movements
are
precision
CNC
controlled
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Micro Hole Drilling in Micro-EDM Set UP
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Micro shaft
Diameter 6 µm, length 300 µm,
WC alloy (its smallness compared
with that of a tiny insect)
Micro tool
Diameter 300 µm, length 600 µm, helix
angle 300, WC alloy
This is what we
may achieve
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Few Shapes that may be produced by Micro Electro Discharge Grinding
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Requirement: EDM to Micro-EDM
Provision for making micro tools in-situ
Reduction the energy per pulse
How to achieve the 2nd requirement?
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Requirements
Micro–EDM requires less than 10-7 J per pulse.
Typical pulse width 1 micro-second or shorter
Energy per pulse (approximately) E = ½ C V2, where C = capacitance and V = applied voltage (for R-C type power supply)
Hence value of C has to be substantially lower than conventional EDM brought down to 10
to 100 pF
The stray capacitance existing in the set up has to be minimized
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A Typical Relaxation Circuit Showing Stray Capacitances
Stray capaciatance between electrode and work tank: C1
Stray capaciatance between electrode and work holder: C2
Stray capaciatance between work holder and work tank: C3
The total stray
capacitance
consists of different
individual stray
capacitances
existing between
the different parts
of the micro-EDM.
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Considering series-parallel arrangement of the three capacitances,
The discharge energy (E) generated in the discharge circuit :
where, C is the capacitance of capacitors C’ is the total stray
capacitance and V is the discharge voltage.
Since all the condenser values are very small (in the order of Pico
Farads), the total stray capacitance (C’) in the circuit plays a
significant role.
To reduce stray capacitance, the micro-EDM is designed in such a
way, so that the processing tank is perfectly insulated.
This means that C1 = 0 and C’ = C2.
Replacing metallic mechanical components around the discharge circuit
with ceramic components does further reduction.
1 32
1 3
'CC
C CC C
= ++
2( ')
2
C C VE
+=
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Material of any hardness can
be cut provided it should be
conductive
High aspect ratio is achieved
Perfect round hole/ Concentric
and accurate holes
No material alteration
Without entrance and exit
deformation/ taper is controlled
No angle limit
No contact between tool and
work-piece
No cutting forces
High precision and good
surface quality
High order of repeatability
Burrless machining
Complicated geometries and
complex 3D contours can be
machined
Advantages of Micro EDM
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Micro EDM Systems
Micro EDM System from Panasonic,
Japan
Capabilities down to 5µm (.0002").
Typical holes boring drilled are sized at 10µm +/-
m (.0004") and 50µm +/- 3 (.002") thru 250µm
(.010")
Thick Tantalum and Tungsten tool on Silicon job.
Micro EDM System from Sarix,
Switzerland
3D Multi-Axis Micro EDM Milling
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Applications of Micro EDM
Micro Molds, Cores for
mould inserts, Dies
Micro-systems for the watch
industry
Medical implants (Tools for
ophthalmic surgery, living
cell manipulations)
Micro-gears, Micro-shafts
Micro-springs
Milling tools for micro cutting
of cavities (micro-milling)
Sharp pointed emitter
Electrode in Ion-beam
equipment for focusing
Micro-Punches (A punch of
diameter 70µm is required in
mass production of ink-jet
printer heads)
Inkjet printer Nozzles (micro-
nozzles)
Precision holes for
applications as: Audiovisual
components, Computer
peripherals
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Applications
EDM Micro Boring
EDM Micro Lathe
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Micro mold Micro gear
Optical fiber connector mech14.weebly.com
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Air Slit of width 200 micron in brass
Micro Slots manufactured by Micro EDM mech14.weebly.com
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How it is done in actual manufacturing?
Example: Micro nozzle fabrication
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Steps of Micro nozzle fabrication
a. Core preparation by µ-WEDG
b. Parting film formation by spraying
silicon oil
f. Finished nozzle
c. Metallic deposition by electroforming
d. Forming outside by µ−WEDG
e. Parting
Parting Film
Deposited Metal
Wire movement
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Thank You
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