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EElectrical lectrical DDischarge ischarge MMachiningachining

(EDM)(EDM)

Lecturer: Lecturer:

ReyadReyad MehfuzMehfuz

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OutlineOutline

1. Review

2. What is EDM?

3. Process Mechanism

4. Elements of EDM

5. Process Parameters

6. Process Characteristics

7. Branches of EDM

8. Advantages

9. Applications

10. Limitations

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ReviewReview

Two types of machining processes

1. Traditional:

• Material removal by the direct mechanical

contact of tool & workpiece.

2. Non-traditional:

• Material removal by thermal, electrical,

chemical, mechanical energies.

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Review contd.Review contd.

Grinding

Drilling

Milling

Turning Electrical Discharge m/c

Electro Chemical m/c

Electron Beam m/c

Laser Beam m/c

Ultrasonic m/c

Water Jet m/c

Traditional m/c Non- Traditional m/c

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What is EDM?What is EDM?

Workpiece material is melted and removed by the heat from high density electrical discharges

Also called Electro-discharge or spark erosion machining

Most Widely used Non-traditional machining process

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Process MechanismProcess Mechanism

1. A shaped tool and workpiece are connected to DC

supply and placed in a dielectric fluid.

2. When the applied voltage is high enough, a localized

breakdown of the dielectric occurs and sparks are

generated across the gap between tool and w/p.

w/p

tool

Spark generates

along the path of

least resistanceTool

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Process Mechanism contd.Process Mechanism contd.

3. These sparks have very high current density and

causes the formation of a plasma channel, vaporising

part of the tool and w/p.

4. The vaporisation produces a high-pressure bubble

that expands rapidly, ejecting a small amount of

material and leaving a small crater on the surface.

5. The momentary local plasma column temperature

ranges from 10,000 to 40,000 OC

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Elements of EDMElements of EDM

• Power supplies

– Pulsed DC

– 10 to 1000 amps

Example:

ONA DATIC D-2030-S.

4 axis- x, y, z & z rotation

EDM Machine

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Work MaterialsWork Materials

Any conductive materials

Elements of EDMElements of EDM

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Tool ElectrodeTool Electrode

1. High electrical

conductivity

2. Ease of fabrication

3. Resistance to wear

4. High melting point

Tm

ElementsElements of EDMof EDM

Copper, Graphite, Zinc, Brass, Tungsten are most common

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Dielectric FluidDielectric Fluid

1. Chemically neutral

2. Low viscosity

3. Absence of toxic

vapor

4. Absence of inflaming

tendency

5. Coolant

6. Flushes the eroded

particle away

ElementsElements of EDMof EDM

Kerosene & De-ionized Water are most common

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Critical Process ParametersCritical Process Parameters

1. Open Voltage (V)

2. Current (I)

3. Resistance (R)

4. Capacitance (C)

5. Discharge Voltage (Vd)

6. Pulse on-time

7. Pulse off-time

8. Spark gap

9. Flushing system2

2

1dCVE =

Energy/ spark:

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Process CharacteristicsProcess Characteristics

• Material Removal Rate (Q):

– Higher I, V, C, Pulse on-time, flushing flow

rate causes higher MRR

timeMachining

removedmaterialofWeightmingmQ =)/(

• Tool wear ratio (TWR):

– Higher I, V, C, Pulse on-time,

causes higher TWR

wearworkpieceofVolume

weartoolofVolumeTWR =

I

Q

V1

V2V3

V3> V2> V1

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Process Characteristics Contd.Process Characteristics Contd.

• Surface finish:

– High frequency spark and low I, V,C gives best

surface finish.

– Economically achievable avg. surface roughness is

0.4 µm.

• Accuracy:

– Sharp corner cannot be achieved

– Taper effect disturbs the machining accuracy

– Usual tolerance value ± 0.03 to ± 0.05 mm.

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Branches of EDMBranches of EDM

Wire EDM

EDM Milling

EDM DrillingWire EDG

Die sinking EDM

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AdvantagesAdvantages

1. High accuracy

2. Surface quality

3. Any conductive materials

4. No hardness limitations

5. Stress-Free and Burr-Free

Cutting

6. Suitable for mold making

7. Suitable to machine difficult

to cut or complex 3d shapes

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ApplicationsApplications

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LimitationsLimitations

1. High specific energy consumption

2. Low MRR

3. Limited to conductive materials

4. Formation of re-cast layer and heat affected zone

5. Difficult to produce sharp corner due to electrode wear

6. Risk of fume and skin irritation hazard to operator

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SummarySummary

• EDM is the most popular non-traditional machining

process

• Material is removed by thermo-electrical process

• Suitable for any conductive materials

• No hardness limitation

• High accuracy and surface finish

• Low material removal rate

• Sharp corner cannot be produced

• Suitable for machining intricate 3D shapes

• Popular for die & mold fabrication

2020

Any Query?