Wire electrical discharge machining (EDM) is a non-traditional machining process that uses electricity to cut conductive materials with a thin copper or brass wire electrode. It works by producing a series of electric sparks between the accurately positioned moving wire and the workpiece, eroding away tiny amounts of material. Key variables that control the process include pulse duration and interval, servo voltage, peak current, and dielectric fluid flow rate. Stratified wires with layered materials can improve cutting speeds and surface quality. EDM is used in aerospace, medical, and other industries for cutting hard metals and shaping complex tooling.

1. Presented by:
Sumaiya
17MEIM024
GE7142

2. › Wire electric discharge machining
› Working principle
› Wire EDM machines
› Wire types and their selections
› Stratified wire
› Benefits of stratified wire
› Process variables
› Process characteristics
› Applications

3. Wire electrical discharge
machining (EDM) is a non-
traditional machining process
that uses electricity to cut any
conductive material precisely
and accurately with a thin,
electrically charged copper or
brass wire as an electrode

4. › The spark theory on a wire EDM is basically is same as
that of the EDM process.
› In wire EDM, the conductive materials are machined with
a series of electric discharges(sparks) that are produced
between an accurately positioned moving wire(the
electrode) and the work piece.
› High frequency pulses of ac or dc current is discharged
from the wire to the work piece with a very small spark
gap through an insulated dielectric fluid(deionized water)

5. › The heat of electrical spark estimated at around 15,000 to
21,000 Fahrenheit, erodes away a tiny bit of material that is
vaporised and melted from the work piece(some of the
wire material is also eroded away).
› These particles(chips) are flushed away from the cut with
the stream of de-ionized water through the top and
bottom flushing nozzles.

6. 1.Computerised numerical control (CNC)
Think of this as BRAIN
2.Power supply
provides energy to the spark
3.mechanical section
worktable, work stand, taper unit, and wire drive mechanism.
4.Dielectric system
the water reservoir where filtration, condition of water
(resistivity/conductivity) and temperature of water is provided and
maintained.

8. Selection of wire in wire EDM should be done by taking
following criteria into consideration:-
› Tensile strength
› Fracture resistance
› Conductivity
› Vaporisation point(low is preferred)

9. › Copper wire
› Brass wire
› Coated or stratified wire
› Molybdenum wire

10. › “if I need the tensile strength of one material and the
conductivity or flush ability of another, why not coat or
plate one with another?”
› Stratified wires have a wire core coated with one or more
layer of different materials.
› Stratified wires usually consist of an alloy with low
vaporisation temperature, plated to a higher tensile
strength core.

11. › special coating to enhance cutting
speeds and surface quality
› Designed to operate at higher speeds
than traditional wire
› Surface quality will be much higher than
traditional brass wire
› Wire burns extremely clean and has a
very smooth wire surface.

12. › Pulse duration
› Pulse interval
› Servo voltage
› Peak current
› Gap voltage
› Dielectric flow rate
› Wire feed rate
› Wire tension

13. During the pulse on time, the
voltage is applied in the gap
between work piece and the
electrode thereby producing
discharge. Higher the pulse on
time, higher will be the energy
applied there by generating
more amount of heat energy
during this period. Material
removal rate depends upon
amount of energy applied
during the pulse on time.
1.Pulse
duration
Reducing Off Time can
dramatically increase cutting
speed, by allowing more
productive discharges per unit
time. However, reducing Off
can overload the wire, causing
wire breakage and instability of
the cut by not allowing enough
time to evacuate the debris
the next discharge.
2.Pulse
interval

14. Servo voltage acts as the reference
voltage to control the wire advances
and retracts. If the mean machining
voltage is higher than the set servo
voltage level, the wire advances, and
it is lower, the wire retracts. When a
smaller value is set, the mean gap
becomes narrower, which leads to an
increase in number of electric sparks,
resulting in higher machining rate
3.Servo
voltage
The current increases until it reaches
pre-set value during each pulse on
time, which is known as peak current.
Peak current is governed by surface
area of cut. Higher peak current is
applied during roughing operation
and details with large surface area.
4.Peak
current

15. Gap voltage, also called open
circuit voltage specifies the supply
voltage to be placed on the gap.
Greater the gap voltage, greater
will be the electric discharge. If the
gap voltage increases, the peak
current will also increase.
5.Gap
voltage Dielectric flow rate is the rate at
which the dielectric fluid is
circulated. Flushing is important
efficient machining. Flushing
pressure is produced from both
top and bottom nozzles.
6.Dielectric
flow rate

16. As the wire feed rate
increases, the consumption
wire as well as cost of
machining will increase. Low
wire speed will cause wire
breakage in high cutting
speed.
7.Wire
feed Within considerable range, an
increase in wire tension
significantly increases the
cutting speed and accuracy.
higher tension decreases the
wire vibration amplitude and
hence decreases the cut width
so that the speed is higher for
the same discharge energy.
However, if the applied tension
exceeds the tensile strength of
the wire, it leads to wire
breakage.
8.Wire
tension

17. › Surface roughness
› Material removal rate
› Kerf(width of cut)
› Wire wear ratio

18. SURFACE ROUGHNESS
Surface roughness is greatly affected
by pulse on time, peak current and
cutting speed in WEDM. Among
these pulse on time is found to be
the most significant parameter
affecting the surface roughness.
MATERIAL REMOVAL RATE
In WEDM the material erodes from the work
piece by a series of discrete sparks between
the work and the tool electrode immersed in
the liquid dielectric medium. These electrical
discharges melt and vaporize minute
amounts of the work material, which are then
ejected and flushed away by the dielectric
fluid. MRR directly increases with increase in
pulse on time (Ton) and peak current (IP)
while decreases with increase in pulse off
time (Toff) and servo voltage

19. KERF
Kerf is one of the important
performance measures in WEDM.
Kerf is the measure of the amount
of the material that is wasted
during machining. It affects the
dimensional accuracy of the
finished part. Kerf of wire EDM
work piece depends on gap
voltage, pulse on time, pulse off
time, wire feed and flushing
pressure
WIRE WEAR RATIO
As WEDM is a thermo- electrical
process in which material is eroded
by a series of sparks between the
work piece and the wire electrode,
along with the work piece material
some particles from wire also will
erode, this phenomenon is called
wire wear and this should be kept to
a minimum. Wire failure occurs in
wire-EDM process as a result of
severity in wire wear rate, which is a
function of discharge current and
discharge time

20. The process is used in the following areas:-
• Aerospace, medical, electronics and semiconductors applications
• Tool and die making industries
• For cutting hard extrusion dies
• In making fixtures, gauges and cams
• Cutting of gears, strippers, punches and dies
• Manufacturing hard electrodes
• Manufacturing micro-tooling for micro-EDM, micro-USM
and other such micro machining applications