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Electric Discharge Machining

Presented By: Srinivas Shenoy H

Reg. No: 100926007

I Semester - MTECH Manufacturing Engg.

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Introduction• Electrical Discharge Machining (EDM) is a controlled metal-removal

process that is used to remove metal by means of electric spark erosion.

• The metal-removal process is performed by applying a pulsating (ON/OFF) electrical charge of high-frequency current through the electrode to the workpiece immersed in dielectric medium.

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Types of EDM Two Main Types1. Conventional EDM or RAM Type

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Conventional EDM or RAM Type

•One of the most widely used nontraditional processes

•Shape of finished work surface produced by a formed electrode tool

•Sparks occur across a small gap between tool and work

•Requires dielectric fluid, which creates a path foreach discharge as fluid becomes ionized in the gap

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Equipment Setup1.Conventional EDM or RAM Type

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DC Pulse Generator or Spark Generator

• Supplies Adequate Voltage Current may vary from 0.5 to 400amp at 40 to 300 volts DC

Pulse Duration 2 to 2000

• Control the recurring rhythm of discharge

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Servo Mechanism

• Maintains the spark gap between tool and work by using servo motor which feeds the tool downward towards the work piece.

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Electrode / Tool Material

• Electrode Materials: Graphite, Tellurium Copper, Brass

• Basic Characteristics: • High Electrical Conductivity• High Thermal Conductivity• Higher Density• High Melting Point• Easy Manufacturability• Cost

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Dielectric Fluid• Dielectric Fluid: Paraffin or Transformer oil, mineral

oils, kerosene, distilled and deionized water etc.

• Essential Requirements: • Electrically non conductive until required breakdown voltage has

reached.• Deionise the spark after the discharge.• Provide Effective Cooling• Cheap• Good Degree of fluidity

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Work Material• Machining Materials Like: steels, super

alloys, refractories

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Equipment Setup Contd….1.Conventional EDM or RAM Type

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Finished EDM’d work pieceThe finished EDM'd workpiece can exhibit several distinct layers.

The surface layer will have small globules of removed workpiece metal and electrode particles adhering to it, which are easily removed.

The second layer is called the “white” or “recast” layer where EDM has altered the metallurgical structure of the workpiece.

The third layer is the heat-affected zone or “annealed” layer. This layer has been heated but not melted.

All of these surface conditions are affected by:• the EDM cycles of on- and off-time• the duty cycle, which is the ratio of on-time relative to total cycle time• the gap distance between the workpiece and the electrode

The electrode is fabricated with the reverse or negative image of the finishedworkpiece cavity.

When EDM'd, this workpiece cavity is measurably larger than the electrode. This dimensional difference is called the overcut or kerf. This kerf dimension is critical during the fabrication of the electrode.

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Applications1.Conventional EDM or RAM Type

•Tooling for many mechanical processes: molds for plastic injection molding, extrusion dies, wire drawing dies, forging and heading dies, and sheet metal stamping dies.

•Production parts: delicate parts not rigid enough to withstand conventional cutting forces, hole drilling where hole axis is at an acute angle to surface, and machining of hard and exotic metals.

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Types of EDM Two Main Types2. Wire EDM or Wire Type

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Wire EDM or Wire Type

• Work is fed slowly past wire along desired cutting path, like a band saw operation.

• CNC used for motion control.

• While cutting, wire is continuously advanced between supply spool and take-up spool to maintain a constant diameter.

• Dielectric required, using nozzles directed at tool-work interface or submerging work part.

• Wire is made of brass, copper or tungsten. (about0.25mm in diameter).

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Equipment Setup2. Wire EDM or Wire Type

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Applications2. Wire EDM or Wire Type

•Ideal for stamping die components .Since kerf is so narrow, it is often possible to fabricate punch and die in a single cut.

•Other tools and parts with intricate outline shapes, such as lathe form tools, extrusion dies, and flat templates

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Advantages

• It Can be applied to all electrically conducting metals & alloys

• Complicated shape can be machined.

• The machining is faster than conventional machining.

• It Can be employed for machining extremely hard material.

• No residual stresses.

• Thin fragile sections such as webs or fins can be easily machined without deforming the part.

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Disadvantages

• Excessive tool wear

• High specific power consumption.

• Machining heats the work piece considerably

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THANK YOU

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EDM Videos• Video 1

• Video 2

• Video 3