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Micro Electrodischarge Machining

also called

Micro-EDM

or

µ-EDM

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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

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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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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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(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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