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Glossary of EDM Related Terms


A class of EDM graphite characterized by a particle and pore size of less then 1 µ , very high strength, isotropy, uniform structure. The most advanced graphite material available.


Exhibiting properties whose values change when measured along different axes. Opposite of "isotropic."


A continuous flow of electricity between an electrode and workpiece. Should an arc occur in EDM, the workpiece, electrode, or both will usually be damaged. An arc is normally visually recognizable as a yellow flash.

Blind Hole

Any hole or cavity cut into the solid which does not connect with other holes.


An abundant, naturally occurring element. Often used in place of the word graphite. Graphite is an allotrope (form) of the element carbon. There are three allotropes of carbon, the other two being amorphous (having no definite form), and diamond.

Center Flow

Pumping of dielectric fluid through either the electrode or the workpiece for flushing.

Center Flushing

A method of flushing dielectric through a center hole in an electrode. For example, as when using a copper tube as an electrode.


A class of graphite characterized by a particle size of more than 100 µ , large pores and voids, a non-uniform structure, and low strength. Not recommended as an EDM electrode material.


Accumulation of debris in the dielectric fluid, causing a decrease in the fluid's dielectric strength.

Copper Graphite

A graphite EDM Electrode material infiltrated with copper.

Copper Tungsten

A porous tungsten material infiltrated with copper.

Corner Wear

In EDM, the corners of the electrode wear the most. Corner wear is the distance up the electrode corners that shows signs of wear.

Dielectric Fluid

In EDM, a light oil in which the work zone is immersed. It fills the gap between the electrode and the work piece and acts as an insulator until a specific gap and voltage are achieved. It then ionizes and becomes an electrical conductor, allowing a current (spark) to flow through it to the work piece. It also serves to cool the work and to flush away the particles generated by the spark.

Electric Discharge Machining (EDM)

A metal removal process using a series of electric sparks to erode material from a workpiece under carefully controlled conditions.


The tool in the EDM process. It must be made from an electrically conductive material. Its form or shape is a mirror image of the finished form or shape desired in the workpiece, with its dimensions adjusted to take into account the amount of overcut that occurs.

Electrode "Growth"

An electroplating action occurring at certain low wear settings which causes work piece material to plate the electrode, causing it to increase in size.

End Wear

A reduction in the length of an EDM electrode occurring during EDM'ing. Can be given as a dimension, or as a percentage of original usable length of electrode.


In EDM, removing the debris from the dielectric fluid before pumping it back into the work tank or through flushing holes in the electrode or workpiece.


Class of EDM graphite characterized by a particle size range from 11µ to 20µ.


Surface condition. Usually given in "micro-inches RMS" (U.S.).

Finish Cut

The final cut made with EDM on the workpiece. The finer the finish desired, the longer it will take for the finish cut. Therefore, roughing cuts, done with conventional equipment or with EDM, should be planned to leave only enough material to be removed by the finish cut to gain final size and surface finished desired.

Flexural Strength

The amount of force required, usually measured in pounds per square inch (psi), to break a specimen by bending it.

Flushing Hole

A hole through the workpiece or electrode used to introduce dielectric fluid to the gap for flushing purpose.

Grain Structure

Used in the graphite industry to refer to the orientation and mass of the individual graphite particles in a graphite system. Used alone, grain refers to the property known as anisotropy.


One of the three forms of carbon. In EDM, a material used for electrodes which has high heat resistance and transfers electric current very efficiently. It is the most popular electrode material and probably the easiest to machine.

Injection Flushing

External flushing method, also known as "jet flushing." Fluid is directed into the gap by means of a flexible tube.


Exhibiting properties with the same values when measured along axes in all directions. Opposite of "anisotropic."

Lateral Flushing

Same as surface, splash, or injection flushing. Directing the flow of dielectric fluid through a shallow blind cavity.


A class of EDM graphite materials characterized by a particle size from 21 µ to 100 µ, anisotropy, non-uniform performance, high porosity.

Metal Removal Rate (MMR)

The rate at which material is removed from the workpiece by EDM'ing. In the U.S., usually expressed in cubic inches/hour.

No Wear

Defined by POCO as a condition under which 1 unit or less of electrode is eroded to every 100 units of workpiece.

Off Time

The time between sparks, measured in microseconds. Too short an off time may result in DC arcing.


A sealed holder for tubular electrodes through which dielectric fluid can be pumped or sucked for center hole flushing.

On Time

The duration time of the EDM spark measured in microseconds.


An EDM cavity is always larger than the electrode used to machine it. The difference between the size of the electrode and the size of the cavity (or hole) is called overcut. When discussing or calculating overcut, be sure to specify whether you are referring to total overcut (diametral overcut) or "overcut per side." Diametral overcut is most commonly used.

Overcut Per Side

One-half of diametral overcut value. It is important to follow this procedure in designing electrodes: (1) Select surface finish setting to determine finishing cut overcut. (2) Design finishing electrode size with overcut allowance. (3) Design roughing electrode, providing for overlap which will leave proper allowance for the finish machining cut to clean up the surface left by the rough cut.

Particle Size

Average diameter of the solid graphite particles in a graphite system. Particle size is determined by the carbonaceous material from which the graphite is produced, and the method of manufacturing. Also known as grain size.

Pressure Flush

Forcing dielectric up through flush holes in the workpiece or down through flush holes in the electrode.

Pulsed Flushing

Flushing that is synchronized with the pulsator of the EDM machine. When a machine is set for this mode (Systematic Coordinated Flushing), pressure flushing takes place only when the quill retracts the electrode from the cavity.


The rapid cooling of the EDM'd surface by the dielectric fluid. Partially responsible for the metallurgical changes forming the "recast layer" or "heat affected zone (HAZ)."

Reverse Burning

The technique of mounting the electrode on the machine table or flush tank and the workpiece on the quill. Used in EDM'ing a blanking punch with female electrode.

Reverse Flushing

Flushing through the flush tank.

Side Wear

In EDM, the wear along the side walls of the electrode.

Silver Tungsten

A porous tungsten material which is infiltrated with silver.

Spark Gap

The distance between the electrode and the work piece when discharges are occurring.

Staged Electrode

A multiple electrode set designed to produce a single cavity. From rougher to finisher each electrode must have dimensions that take into account leaving sufficient metal for the last electrode to produce the required dimensions.

Stepped Electrode

An electrode constructed in such a manner as to allow the roughing and finishing of a through-hole cavity in a single set up. The smaller front section is used to rough out the cavity and the larger rear portion is used for finishing.


A class of EDM electrode materials characterized by a particle size from 6 µ to 10 µ.

Surface Flushing

The relative roughness or smoothness of the machined surface. Usually measured in microinches RMS in the U.S.

Surface Finishing

The use of nozzles or hoses to direct jets of dielectric at the cutting area to flush away the debris. Usually employed while pulsating the electrode.

Tellurium Copper

An alloy of copper and tellurium.

Through-Hole Flushing

Use of pre-drilled hole in the workpiece to inject dielectric fluid up toward the gap by injection flushing or down from the gap by suction flushing.


A metal used in pure or near pure state as an electrode material. Melting point is 3400ºC. Also infiltrated with copper or other materials to form electrode materials with various qualities.


A class of EDM graphite characterized by a particle size from 1 µ to 5 µ, uniform structure and high strength.

Wire EDM, Wirecut

The electrode is a moving metal wire usually drawn across the gap from one spool to another.


Any part on which EDM is being used to make holes or cavities.

** This information and definition list was provided by Poco Graphite, Inc.**