Electric discharge machining (EDM) is a machining process that uses electrical discharges to remove material from a conductive workpiece. There are two main EDM processes - die sinking and wire cutting. Die sinking involves an electrode progressively eroding a workpiece cavity to its shape. Wire cutting uses a continuously fed wire electrode to cut complex profiles. EDM can machine all conductive materials regardless of hardness and produces parts with good accuracy and surface finish.

1. Electric
Discharge
Machining

2. Electric
Discharge
Machining

3. EDM
• The EDM process we know today started
with the observations of Joseph Preistly in
1770. He noticed that electrical discharges
had removed material from the electrodes
in his experiments. This is also known as
electro-discharge erosion.
In the 1940's Soviet researchers developed
a machining process that formed the
foundation for modern EDM.

4. Principle
• EDM is a machining process which
consists in removing material from a
workpiece, using electrical discharges as
the means of machining. This technique
is characterized by its aptitude for
machining all materials that conduct
electricity (metals, alloys, carbides,
graphite, etc. whatever their hardness
may be. To machine with this process, 4
items are required:

5. EDM

6. Die electric fluid
• The purpose of the dielectric (water or
mineral oil) is to lower the temperature
in the machining area, remove the
residual metallic particles, and enable
sparks to be created

7. Electrical discharge
machining
• Produced by a spark generator, the
sparks at regular intervals create a
succession of craters in the work piece.
Each spark produces a temperature
between 8,000 and 12,000° C. The size of
the crater depends on the energy turned
out by the spark generator. The range of
the sparks varies from a few microns to 1
mm.

8. The EDM process takes place
in 6 stages
• 1 The electrode approaches the work
piece. The two units are energized.

9. • 2 Concentration of the electrical field
towards the point where the space
between the electrode and work
The EDM process takes place
in 6 stages

10. The EDM process takes place
in 6 stages
• 3 Creation of an ionized channel
between the electrode and workpiece.

11. The EDM process takes place
in 6 stages
• 4 Breakdown of the spark. The work
piece material melts locally and
disintegrates. The electrode only wears
out slightly.

12. The EDM process takes place
in 6 stages
• 5 The current is cut off, causing
implosion of the spark.

13. The EDM process takes place
in 6 stages
• 6 Evacuation of the metallic particles by
flushing with dielectric.

14. Surface finish and
machining speed
• The surface finish depends on the
dimensions of the sparks. If they are
energetic, the surface finish will be
rough, but on the other hand the speed
of machining will be high.

15. Surface finish and
machining speed
• If the sparks are of low energy, the
surface finish will be fine, but machining
speed will be low.

16. Surface finish and
machining speed
• The finest surface finishes will be of the order
of Ra 0.10, and the visual effect is almost like
a mirror finish. Standard surface finishes, that
are easy to obtain, are equivalent to Ra 0.8/1
(N5 - N6).
• Machining speeds in EDM are moderate.
Depending on the energy of the sparks,
material removal rates range from 1 to
several thousand cubic millimeters per
minute.
• Although it uses electrical sparks, the process
entails no risk for users or the environment

17. Surface finish and
machining speed

18. Machining Type
There are two distinct EDM processes,
both using the same physical principle:
• Die sinking
• Wire cutting

19. Die sinking
• EDM die sinking reproduces, in a metallic work piece, the
shape of a tool called electrode.
• Injection molds for plastic parts are very frequently
machined by die sinking.
• The shape given to the electrode is that of the object that is
going to be molded.
• In the machining area, each discharge creates a crater in
the work piece (material removal) and an impact on the
tool (wear of the tool/electrode).
• There is never any mechanical contact between the
electrode and work piece.
• The electrode is usually made of copper or graphite.

20. Die sinking

21. Wire cutting
• EDM wire cutting uses a metallic wire
(electrode) to cut a programmed contour in a
work piece.
• Extrusion dies and blanking punches are very
often machined by wire cutting.
• Cutting is always through the entire work
piece.
• To start machining it is first necessary to drill
a hole in the work piece or start from the
edge.
• In the machining area, each discharge
creates a crater in the work piece (material
removal) and an impact on the tool (wear of

22. Wire cutting
• The wire can be inclined, thus making it
possible to make parts with taper or
with different profiles at the top and
bottom.
• There is never any mechanical contact
between the electrode and work piece.
• The wire is usually made of brass or
stratified copper, and is between 0.02
and 0.03 mm diameter

23. Wire cutting

26. Applications-Die Sinking

27. Applications-Wire EDM
.

28. Types of applications using EDM

29. Types of applications using EDM

30. Which industries use EDM?

31. Die sinking
• Die sinking is a method involving electrical discharges
between an electrode and a conductive work piece in a
dielectric fluid. Material is removed from the work piece by
a controlled electrical spark generated in the machine’s
power supply and discharged between an electrode and
work piece. The electrode progressively “erodes” the
workpiece, producing a cavity the same contour or shape
as the electrode. In fact, making die cavities was such a
common application for ram EDM in the early days that it
was often called die sinking. The machines are still often
referred to as die sinkers. Regardless of the application,
the work piece may be of any material, no matter how
hard, as long as it is electrically conductive. However,
machining speed will be determined by the material’s
melting temperature, as well as its electrical and thermal
conductivity.

32. Die sinking
• For EDM, there must always be a small space, known as the spark gap,
between the electrode and the workpiece. The gap is filled with a
circulating dielectric fluid. On a ram EDM machine, this fluid is
usually oil. The dielectric fluid becomes ionized during the course of a
discharge. As ionization occurs, positively charged ions strike the work
piece, increasing the temperature at the surface of the workpiece and
electrode. The temperature is so high at the surface, often reaching
more than 10,000° C, that it causes the work piece to melt or vaporize.
A bubble of hydrogen gas begins to form. When current flow is turned
off, the hydrogen bubble implodes. The force of this implosion forces
molten metal to be evacuated from the surface of the work piece and
flushed away by the dielectric fluid. Although most of the molten metal
created by the discharge is carried away from the work piece, a small
amount fuses onto the machined surface, creating what is called the
“recast layer.”
•

33. Die sinking
• Fine surface finishes can be achieved with current, conventional
EDM technology. The technique involves copper rather than the
more commonly used graphite electrode material. Copper lends
itself to fine finishes with conventional EDM because it does not
have the granular structure of graphite. Copper electrodes can
achieve a “mirror” or “glazed” finish (that is, 2µinch Ra) on
cavities with a surface area of 2 square inches or smaller.
• As the work area becomes larger, however, the finish will
deteriorate because a copper electrode cannot easily be contained
in the cavity. This is due, in part, to the thermal expansion
characteristics of copper. As a result, a fine finish becomes
increasingly difficult to achieve as cavity size increases.

34. Features of the Wire EDM
Process
• Low work holding forces
• Low cutting forces
• Very accurate process tolerances held +/- 0.0001"
• Complex profile capability
• No tool wear (the wire is continually replenished)
• Environmentally friendly (by products are easily
recycled)
• Hardened materials are easily machined

35. Wire EDM
• Depending on the accuracy and surface finish
needed a part will either be one cut or it will be
roughed and skimmed. On a one cut the wire
ideally passes through a solid part and drops a slug
or scrap piece when it is done. This will give
adequate accuracy for some jobs but most of the
time skimming is necessary. A skim cut is where
the wire is passed back over the roughed surface
again with a lower power setting and low pressure
flush. There can be from one to nine skim passes
depending on the accuracy and surface finish
required.

36. Wire EDM
• Usually there are just two skim passes. A skim
pass can remove as much as 0.002" of material or
a as little as 0.0001". During roughing ( i.e. the
first cut) the water is forced into the cut at high
pressure in order to provide plenty of cooling and
eliminate eroded particles as fast as possible.
During skimming (accuracy / finish cuts) the
water is gently flowed over the burn so as not to
deflect the wire.

37. What Is Small Hole EDM?
• Small hole EDM is a specialized component of electrical
discharge machining. A small hollow electrode spins about
a spindle much like a drill and drill bit (EDM drill). The
electrode is electrically charged by a servo-controlled
generator producing the spark. Water based dielectric
flushes through and around the electrode providing a
controlled environment for the spark to jump to the work
piece. The electric spark erodes the surface of the work
piece creating very small pockets. Eventually millions and
millions of these microscopic pockets create the small
hole. The size of the hole is controlled by the diameter of
the electrode. The location and depth of the holes are
driven by CNC ISO codes, reducing and eliminating
operator error. Machines shown have automatic electrode
changers for unattended machining.

38. Applications
• Small hole EDM is in many ways similar to a drilling operation but it
offers the advantages of EDM. Very low machining and work piece
hardness are not barriers to performance. A short list of common
applications follows.
• Addition of wire EDM start holes after heat treating
• Removal of broken drill bits
• Placement of holes too small/difficult for conventional drilling
• Coolant holes in hardened machine tool bits
• Taps
• End Mills
• Drill

39. Small Hole EDM

40. Advanced Wire E.D.M.

41. Advanced Wire E.D.M.

42. Advanced Wire E.D.M.

43. Advanced Wire E.D.M.