Electrodischarge Machining (edm)

Electrical Discharge Machining (EDM)

Lecturer:

Reyad Mehfuz

Outline 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 2

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Review 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. Traditional m/c Turning

Non- Traditional m/c Electrical Discharge m/c Electro Chemical m/c

Milling

Electron Beam m/c Laser Beam m/c

Drilling

Ultrasonic m/c Water Jet m/c

Grinding 4

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What is EDM? Most Widely used Non-traditional machining process Workpiece material is melted and removed by the heat from high density electrical discharges

Also called Electro-discharge or spark erosion machining 5

Process Mechanism Spark generates along the path of least resistance Tool

tool

w/p

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. 6

3

Process Mechanism contd.

3.

4.

5.

These sparks have very high current density and causes the formation of a plasma channel, vaporising part of the tool and w/p. The vaporisation produces a high-pressure bubble that expands rapidly, ejecting a small amount of material and leaving a small crater on the surface. The momentary local plasma column temperature ranges from 10,000 to 40,000 OC

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Elements of EDM EDM Machine • Power supplies – Pulsed DC – 10 to 1000 amps

Example: ONA DATIC D-2030-S. 4 axis- x, y, z & z rotation 8

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Work Materials

Elements of EDM

Any conductive materials

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Tool Electrode

Tm

Elements of EDM

1. High electrical conductivity 2. Ease of fabrication 3. Resistance to wear 4. High melting point

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

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5

Elements of EDM

Dielectric 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

Kerosene & De-ionized Water are most common 11

Critical Process Parameters 1. 2. 3. 4. 5. 6. 7. 8. 9.

Open Voltage (V) Current (I) Resistance (R) Capacitance (C) Discharge Voltage (Vd) Pulse on-time Pulse off-time Spark gap Flushing system

Energy/ spark:

E=

1 CVd2 2 12

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Process Characteristics V3> V2> V1

Q ( gm / min) =

Weight of material removed

V2

V3

• Material Removal Rate (Q): Q

Machining time

– Higher I, V, C, Pulse on-time, flushing flow rate causes higher MRR

V1 I

• Tool wear ratio (TWR): TWR =

Volume of tool wear Volume of workpiece wear

– Higher I, V, C, Pulse on-time, causes higher TWR 13

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. 14

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Branches of EDM Die sinking EDM

EDM Milling

Wire EDM

Wire EDG

EDM Drilling

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Advantages 1. 2. 3. 4. 5. 6. 7.

High accuracy Surface quality Any conductive materials No hardness limitations Stress-Free and Burr-Free Cutting Suitable for mold making Suitable to machine difficult to cut or complex 3d shapes

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Applications

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Limitations 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 18

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Summary • 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 19

Any Query? 20

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