ELECTRICAL DISCHARGE MACHINING:

The spark eroding, die sinking, wire burning or wire erosion is also called as Electrical discharge machining (EDM).

The full form of EDM or EDM Machining is electrical discharge machining.

Other than any processes this is an ideal process for machining complex shapes and contours that cannot be handled by convention cutting technology.

This process has been developed in the mid 20th century by Soviet researchers.

This an modern EDM process that we are familiar with.

Electrical discharge machining process
Fig. 1 Electrical discharge machining process

The electrical discharge created between an electrode and a workpiece is involved in this process.

The temperatures of this process ranges around 8000 to 12000 degrees Celsius.

This process has one quality, it can effectively melt almost any material.

The heat will just treat the surface of the material through localizing and controlling the spark.

It is possible to obtain desired shape using electrical discharges (sparks) through this metal fabrication process .

Material is thrown out from the work piece by a series of rapidly recurring current discharges between two electrodes, separated by a dielectric liquid and subject to an electric voltage.

The intensity of the electric field in the volume between the electrodes becomes greater, when the voltage between the two electrodes is increased.

Then it causes dielectric break down of the liquid, and produces an electric arc.

GENERALITIES:

For hard metals or those that would be very difficult to machine with traditional techniques then EDM plays important role .

Electrical discharge machining process generally works with materials which are electrically conductive.

Metal or metal alloy such as titanium, hastelloy, kovar, and incone, electrical discharge machining method were used.

Holes produced by EDM in injection nozzle
Fig. 2 Holes produced by EDM in injection nozzle

EDM is mostly included in non-traditional or non-conventional group of machining.

A series of breakdown and restoration of the liquid dielectric in between the electrodes can go through the EDM.

The control system of the electrode may fail to react quickly enough to prevent the two electrodes from coming into contact, with a consequent short circuit.

TYPES OF EDM:

SINKER EDM:

Convention EDM or ram EDM is also referred as Sinker, which is the one type of EDM.

The electrically charged electrode essentially ‘sinks’ into the metal component in the electrical discharge machining process.

The discharged electrical pulses jump to the work piece and remove particles in all EDM process.

With unique finishing capabilities of the graphite, copper tungsten or brass the electrode is made.

From any electrically conductive material sinker EDM can form parts.

The equipment can handle miniscule objects all the way to dimensions as tall as 9-feet.

WIRE EDM:

The projects which are having extremely tight tolerances, for that the latest wire EDM equipment are ideally suited.

Also it contains material with low stress thresholds, or require specific finishing or surface treatments.

Wire Electrical discharge machining process
Fig. 3 Wire electrical discharge machining process

A straight wire strand capable of cutting a linear line directly through material is used in the wire electrical discharge machining.

The cutting tolerance and surface finish are directly related to electrical discharge machining cutting processes.

Through the number of passes from the EDM machine the Wire electrical discharge machining cutter is controlled.

The material which is too brittle to be stamp cut or machined conventionally for them the Wire EDM machining can be used.

For high-volume and multi-layer cutting of material, electrical discharge machining capabilities are very important.

FAST HOLE DRILLING EDM:

For the purpose of producing fast, accurate, small, and deep holes the fast hole drilling EDM was designed.

Spiral cavity produced by EDM
Fig. 4 Spiral cavity produced by EDM

It is conceptually similar to sinker EDM but the electrode is a rotating tube conveying a pressurized jet of dielectric fluid.

It can make a hole an inch deep in about a minute and is a good way to machine holes in materials too hard for twist-drill machining.

For the purpose of producing cooling holes into aero blades and other components in the aerospace industry, the drilling type EDM is mostly used.

Also for drilling holes in industrial gas turbine blades, in molds and dies, and in bearings EDM plays important role.

ADVANTAGES OF EDM:

It has the ability to machine complex shapes otherwise it will be get much difficult to produce with conventional cutting tools.

Machining of extremely hard material to very close tolerances.

Delicate sections and weak materials can be machined without perceivable distortion as there is no direct contact between tool and work piece .

Due to the redundant finishing process there is a good surface finish.

DISADVANTAGES OF EDM:

Difficulty finding expert machinists.

The slow rate of material removal.

By use of combustible oil based dielectrics there is potential fire hazard associated .

For ram/sinker EDM it takes additional time and cost for creating electrodes.

Due to electrode wear, reproducing sharp corners on the workpiece will not get easy.

Specific power consumption is very high. Power consumption is high.

“Overcut” is formed.

Excessive tool wear occurs during machining.

Electrically non-conductive materials can be machined only with specific set-up of the process.

APPLICATIONS:

With its ability to create precise and unique shapes, electrical discharge machining process has been used by many industries in their manufacturing processes.

FOR DIE MAKING:

Dies are tools used to cut or shape materials into a solid product.

Electrical discharge machining is used to create these dies, despite the size or commoness of the shape needed.

FOR MOLD MAKING:

Molds are containers that transform liquid or substance into the shape of the container.

By using electrical discharge machining we can achieve the molds dimensions and depth.

FOR SMALL HOLE DRILLING:

Without electrical discharge machining drilling small holes will not be possible.

Creating small shapes accurately makes it ideal for drilling the exact size of holes.

In order to achieve these applications, electrical discharge machining drills and tubes are necessary.

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