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PARIKH KRUTIK R.

ROLL NO:931

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Electrical Discharge Machining (EDM) is acontrolled metal-removal process ,that is used toremove metal by means of electric spark erosion.In this process an electric spark is used as the

cutting tool to cut (erode) the work-piece toproduce the finished part to the desired shape.The metal-removal process is performed byapplying a pulsating (ON/OFF) electrical chargeof high-frequency current through the electrodeto the work-piece.This removes (erodes) very tiny pieces of metalfrom the work-piece at a controlled rate.

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EDM spark erosion isthe same as havingan electrical shortthat burns a small

hole in a piece of metal it contacts.With the EDM processboth the work-piecematerial and theelectrode materialmust be conductorsof electricity.

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The EDM process can be used in two differentways:1. A pre shaped or formed electrode(tool),usually made from graphite or copper, isshaped to the form of the cavity it is toreproduce. The formed electrode is fed verticallydown and the reverse shape of the electrode iseroded (burned) into the solid work piece.2. A continuous-travelling vertical-wireelectrode, the diameter of a small needle or less,is controlled by the computer to follow aprogrammed path to erode or cut a narrow slotthrough the work piece to produce the requiredshape.

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The process can be used to machine any workmaterial if it is electrically conductiveMaterial removal depends on mainly thermalproperties of the work materialIn EDM there is physical tool ,and geometry of the tool is positive impression of the hole orgeometric feature machinedThe tool has to be electrically conductive as well.The tool wear once again depends on the thermalproperties of the tool material.Though there is a possibility of taper cut andover cut in EDM ,they can be controlled andcompensated

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dielectric fluid shouldprovide an oxygen freemachining environment.further it should haveenough strong dielectricresistance so that it doesnot breakdownelectrically too easily butat the same time ionizewhen electrons collidewith its molecule.Moreover, duringsparking it should bethermally resistance aswell.

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Generally kerosene and de-ionized wateris used as dielectric fluid in EDM . Tapwater cannot be used as it ionizes easilyand thus breakdown occurs due topresence of salts as impurities. Dielectricmedium is generally flushed around thespark zone. It is also applied through thetool to achieve efficient removal of molten metal.

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Electrode material should such that it wouldnot undergo much tool wear when it isimpinged by positive ions. Thus thelocalized temperature rise has to be less bytailoring or properly choosing its propertiesor even when temperature increases ,therewould be less melting . Further , the tool

should be easily workable as intricate shapegeometric features are machined in EDM

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Thus the basic characteristics of materialsare:High electrical conductivity electrons are

cold emitted more easily and there is lessbulk electrical heating.High thermal conductivity: for the sameheat load , the local temperature rise would

be less due to faster heat conducted to thebulk of the tool and thus less tool wear.

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Higher density-for the same heat load andsame tool wear by weight there would be lessvolume removal or tool wear and ths lessdimensional loss or inaccuracy.High melting point- high melting point leadsto less tool wear due to less tool materialmelting for the same heat load

Easy manufacturabilyCost-cheap

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Electrolytic oxygen free copperGraphite

Tellurium copper 99% Cu+0.5%telluriumBrass

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Dielectric reservoir ,pump and circulationsystemPost generator and control unit

Working tank with work holding deviceX-y table accommodating the working tableThe tool holderThe servo system to feed the tool

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Complex shapes that would otherwise bedifficult to produce with conventionalcutting tools

Extremely hard material to very closetolerancesVery small work pieces whereconventional cutting tools may damagethe part from excess cutting toolpressure.

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There is no direct contact betweentool and work piece. Thereforedelicate sections and weak materials

can be machined without anydistortion.A good surface finish can be obtained.

Very fine holes can be easily drilled.

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The slow rate of material removal.The additional time and cost used forcreating electrodes for ram/sinker EDM.

Reproducing sharp corners on the work-piece is difficult due to electrode wear.Power consumption is high.Excessive tool wear occurs duringmachining.

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Cutting small holes.Blanking parts from sheets.Cutting off rods from materials withpoor mach inability Machining of cavities and dies.Flat or firm grinding

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