EDM Glossary

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A [ Words starting with A ]
Amperage (A)	The current that actually machines material in EDM.
Angstrofine	An advanced grade of EDM graphite characterized by a particle size of less than 1 micron (0.000039") and having very high tensile strength, isotropy, and uniform structure.
Anisotropic	Exhibiting properties whose values change when measured along differing axes.
Anode	Often used to describe the cutting tool (electrode) in the EDM process. The positive terminal of an electrolytic cell or battery.
Arc	A continuous flow of electrical current, visually recognizable as a yellow flash, between an electrode and workplace. An arc will damage both the electrode and workpiece.
Arc guard	Same as arc suppressor.
Arc suppressor	A circuit in the EDM power supply that reduces or suppresses an arc from occurring.
Automatic Tool (Electrode) Changer (ATC)	A device used with computer numerically controlled machine tools (EDM) to change tools automatically to provide automatic operation.
Average current	The average value of all the minimum and maximum peaks of amperage in the spark gap, as read on the ammeter.

B [ Words starting with B ]
Billet	A large, uncut block of graphite, usually the size as produced by the manufacturer.
Blind hole	Any hole or cavity cut into a solid shape which does not connect with other holes.
Breakthrough	The exit point of a through-hole cavity.
Burning	Slang term for EDM.

C [ Words starting with C ]
Capacitor	An electrical component that stores current and discharges when they become full. Traditionally used for EDM'ing tough to machine and exotic material. In some EDM power supplies, a bank of capacitors are connected across the machining gap.
Carbon	An abundant, naturally occurring element. Often used in place of the word graphite. Graphite is a form of the element carbon. There are four forms of carbon.
Catalyst	A material that causes an increase in the rate of a reaction due to its presence, but is unchanged at the end of the reaction. In EDM, catalyst refers to particulates that aid in establishing a current path in the dielectric fluid.
Cathode	In EDM, a term to denote the workpiece, or the negative terminal of a battery.
Center Flushing	A method of flushing dielectric through a center hole in an electrode or workpiece.
Circuit	A continuous path of electrical current.
Coarse	A class of graphite characterized by a particle size of more than 100 µm large pores and voids, a non-uniform structure, and low strength. Not recommended as an EDM electrode material.
Collet	A device used to hold round shank electrodes.
Colloidal Suspension	Tiny particles produced during EDM'ing form a colloidal suspension in the dielectric fluid.
Common Metals	The first group of metallic electrode materials. Includes copper, brass, and zinc.
Composite	In EDM, copper tungsten is an example of a metallic composite. The copper and tungsten do not alloy, but are simply combined together. Copper graphite is a metallic/carbon composite.
Condenser	Same as capacitor.
Conductor	Any material that will carry electrical current is a conductor.
Contamination	The accumulation of debris in the dielectric fluid, which can cause instability and a decrease in the fluid's dielectric strength.
Copper Graphite	Graphite electrode material that is infiltrated with copper. Use for very fine detail EDM'ing, but will also wear faster than standard graphite.
Copper tungsten	A porous tungsten material infiltrated with copper.
Core	The slug that remains after EDMing with an electrode that has a flush hole in it.
Coreless Machining	Refers to the Wire EDM'ing all the material from a shape by stepping from the center instead of producing a "slug". Similar to a pocketing routine in milling.
Corner Wear	In EDM, the comers of the electrode wear the most. Corner wear is the distance up the electrode corners that show signs of wear.
Crater	The small circular impressions that are formed by each individual spark as material is removed that creates the random EDM'd surface on the workpiece.
Inches Cube/Hour (in3/hr)	The units of measure used to describe the rate of metal removal from the workpiece.

D [ Words starting with D ]
DC Arcing	Same as arc.
DC (Direct Current)	Constant polarity current, as opposed to Alternating Current (AC), which changes polarity from negative to positive in cycles.
DDM	Is the Makino "Process" that produces HQSF (High Quality Surface Finishes).
Deionization	A return of the condition of the dielectric to a non-conductive state. Failure to accomplish Deionization during the off-time of the spark is responsible for DC arcing.
Depth of Craters	The distance from the peaks to valleys on an EDM'd surface.
Depth-to-diameter ratio	In small hole EDMing, the ratio of the depth of a blind hole compared to the diameter of the electrode used to make the hole.
Dielectric Fluid	In EDM, a liquid medium that fills the gap between the electrode and workpiece and acts as an insulator until a specific gap and voltage are achieved. Used to remove chips and cool the electrode/wire and workpiece. It then ionizes and becomes an electrical conductor, allowing a current (spark) to flow through it to the workpiece. It also serves to cool the work and to flush away the particles generated by the spark.
Dielectric Strength	The voltage at which the insulating qualities of a material break down. In EDM, a specification applied to dielectric fluid.
Discharge	The EDM spark.
Discharge Channel	The conductive pathway formed by ionized dielectric and vapor between the electrode and workpiece.
Discharge Dressing	The process used to dress worn electrodes prior to finishing. The machine is programmed to move the worn electrode to a dressing block in the work tank. After dressing, the electrode is returned to the cavity for the finishing cut. Often used for forming micro diameter electrodes for small hole applications.
Disintegrator	An EDM technology used for removing taps and other broken tools for salvage purposes. The original EDM application.
Dither	A slight motion in the machining axis (Z) used to improve cutting stability on manual EDM machines.
Dressing	The re-machining of the face of an electrode to sharpen its detail after it has been used to produce a cavity. Electrodes used to make a through-hole are often dressed at the worn end.
Duty Cycle	The percentage of the on-time relative to the sum of the on-time and off-time setting for a particular cut.

E [ Words starting with E ]
Edge finder	An electrically activated device on an EDM machine to aid in the accurate location of the workpiece with respect to the electrode.
EDM	See Electrical Discharge Milling or Machining.
Efficiency	A measure of EDM performance which varies with the on and off time settings for an EDM cut. Duty cycle.
Electrical Discharge Grinding (EDG)	An EDM machine resembling a surface grinder but Using a wheel made from electrode material. Can also be done with a horizontal spindle attachment (mounted on the quill of a conventional EDM machine) which has a built-in motor drive for the electrode wheel.
Electrical Discharge Machining (EDM)	A metal removal process using a series of electric sparks to erode material from a workpiece under carefully controlled conditions.
Electrical Resistance	The resistance of the flow of electricity through material. Measured in ohms.
Electrode	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 over "burn" that occurs.
Electrode Growth	A plating action occurring at certain low wear settings which causes workplace material to build up on the electrode, causing it to increase in size.
Electrode Management Technology (EMT)	Automatic management of electrodes for replenishment in flexible manufacturing environment.
Electroforming	An electroplating process used to make metal EDM electrodes.
Electrolyte	A normally conductive liquid or gas.
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 the original usable length of the electrode.
Eroding	Material removal by the EDM process.
Exit point	The point at which the electrode pieces the workpiece in through hole EDM.
Exotics	The third group of metallic electrode material types used in EDM. Includes all rarely used metals such as tantalum, nickel, molybdenum, silver and even gold.

F [ Words starting with F ]
Farad	The unit of electrical capacitance. Used to rate the energy storing capacity of a capacitor and usually rated in microfarads. One farad = the capacitance between whose plates there appears a potential of one volt when charged by one amp/second.
Filtering	Removal of chips and other debris from the dielectric fluid before re-circulating it back into the Work Zone and Spark Gap.
Fine	A class of EDM graphite characterized by a grain size from 11µ to 20 µ.
Finish	The surface texture produced by EDM'ing. Usually given in µin Aa or Ra (U.S.).
Finish or Skim Cut	The final cut made with EDM on the workpiece. 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 finish desired.
Fire Extinguisher	Used in today's advanced EDM Sinking systems to allow for safer unattended operation.
Flashpoint	The temperature at which any flammable material will burst into flame. An important factor in selecting a dielectric fluid.
Flexural Strength	A property of a solid material that indicates its ability to withstand a flexural or transverse load.
Float Switch	An adjustable float switch that monitors the depth of the dielectric fluid in the tank.
Flush Pot	A multipurpose box-like fixture which is clamped to the machine worktable. Primarily used when EDM'ing through-holes. The workpiece is clamped to its top, usually over an opening that will permit an electrode to pass through the workpiece without interference from the tank's top plate. It is connected to the dielectric system and can be used for either suction flushing or pressure flushing.
Flushing	Describes the dielectric movement through the spark gap that is necessary in EDM to cool the electrode/wire and workpiece and remove machining chips and debris caused by the ED machining process.
Flushing Hole	A hole through the workpiece or electrode used to introduce dielectric fluid to the gap for flushing purpose.
Flushing Pressure	The pressure supplied by pumps in the dielectric system supply fluid to the spark gap.

G [ Words starting with G ]
Gap (Spark Gap)	The distance between the electrode and workpiece when the spark occurs.
Gap voltage	This can be measured as two different values during one complete cycle. The voltage, which can be read across the electrode/workpiece gap before the spark current begins to flow, is called the open gap voltage. The voltage that can be read across the gap during the spark current discharge is the working gap voltage.
Generator	Another term for EDM power supply.
Glazed Finish	A Makino term that refers to a mirror or reflective EDM'd surface finish < 6 µinch Ra (1µmRmax) that is produced when charged particles in the gap are used with orbital motion to electro-mechanically polish the surface. Extreme accuracy and rigidity is required in order to maintain a precise spark gap.
Grain	In manufactured carbon and graphite product technology, a region in a carbon or graphite body that is identifiable as being derived from a particle or filler.
Graphite	One of the four 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.

H [ Words starting with H ]
Head	That part of the EDM machine tool in which the quill or Ram (Z Axis) travels.
Heat-Affected Zone (HAZ)	The layer below the recast layer. This layer has been subjected to elevated temperatures that have altered the properties of the material.
Hertz (Hz)	The international term for one complete electrical cycle or frequency.
HQSF™	Is Makino's High Quality Surface Finish that uses Diffused Discharge Machining (DDM) technology.
Hunting	Erratic movement of the EDM quill during a cut that can be caused by poor flushing conditions in the gap, servo response set for too much sensitivity, and build-up of carbon deposits on the bottom of the cavity being EDM'd.

I [ Words starting with I ]
Intelligent Expert System(IES)	Intelligent Expert System is Makino's software driven adaptive control system designed to automatically correct machining variables during machining. Some EDM builders for their adaptive control system use "Fuzzy Logic". One weakness is that Fuzzy Systems are hardware dependant and become obsolete.
Injection	The introduction of dielectric fluid to the gap under pressure.
Injection flushing	An external flushing method, also known as jet flushing. Fluid is directed into the gap by means of a flexible tube.
Initiation voltage	Same as open gap voltage.
Insulator	A substance which blocks the flow of electric current.
Ion	An atom or group of atoms that carries a positive or negative charge as a result of having lost or gained one or more electrons. It is ionization of the dielectric fluid that provides the conductive path for the EDM spark.
Ionization	The process by which the dielectric fluid become electrically conductive between the electrode and workpiece.
Ionization Delay Time	The inconsistent delay between ionization start and completion times and is affected by changing Gap conditions.
Ionization Time	The time from the application of voltage until current begins to flow.
Ionization Voltage	The voltage at which current flow begins across the gap.
Ionized Path	The path of electrically conductive dielectric molecules between the two points on the electrode and workpiece through which the spark current will flow.
Isotropic	Exhibiting properties with the same values when measured along axes in all directions. Opposite of anisotropic.

J [ Words starting with J ]
Jump	Exhibiting properties with the same values when measured along axes in all directions. Opposite of anisotropic.

K [ Words starting with K ]
None

L [ Words starting with L ]
Lateral Flushing	Same as surface or splash flushing. Directing the flow of dielectric fluid through a hose pointed at the electrode in order to remove chips and swarf in a [shallow] blind cavity.
"LL" Generator	Is Makino's anti-electrolysis generator and stands for "Layer Less".
Low Wear	The result of certain settings for EDM machining which produces a very low degree of wear by plating the electrode with melted work material. In some cases less than 1%, which is also known as no-wear.

M [ Words starting with M ]
Machine Tool	It performs the purely mechanical functions and, along with the dielectric system and the power supply, makes up the complete EDM.
Machining Rate	Same as Metal Removal Rate. The rate at which material is removed from the workpiece by EDM.
Mean Overcut	The average of top and bottom Overcut.
Medium Grade	A class of EDM graphite materials characterized by a particle size from 21m to 100m, anisotropy, non-uniform performance, and high porosity.
Metal Removal Rate (MRR)	The rate at which material is removed from the workpiece by EDM. In the U.S., usually expressed in cubic inches/hour (in/hr).
Metallic Composite	A non-alloyed combination of metals, such as copper tungsten.
MG CNC Control	Makino Graphic CNC Controls. First with GUI style operator interface and simplified macro driven software.
Micro-farad	One-millionth of a farad.
Micron Machining	Makino term for precision EDM machining.
Micron, Micrometer (µm)	A unit of length equal to one-millionth of a meter or 0.00003973". Similarily, a micro inch (µinch) is one-millionth of an inch (0.000001").
Micro second (µs)	One-millionth of a second (0.000001 sec.) used to control each EDM spark from the generator µs of On & Off-Times
Millisecond (ms)	One thousandth of a second (0.001 sec.).
Miss	A pulse that does not produce machining due to too great a gap.
Model Data	Provides the programmer the ability to pre-select from 1 to 15 burning conditions (roughing and finishing) based on electrode size and surface finish with ONLY two inputs.
Model Plan	Canned Cycles (Macros) that simplify EDM Programming through the use of commonly used Machining Positioning and Measuring Models (or Functions) that can be programmed easily using Makino's Graphic User Interface.
Monitor	In EDM, any mechanical or electrical device which is used to indicate various operating conditions, i.e., ammeters, indicators, lights, pressure gages.
Multiple electrodes	The simultaneous use of electrodes to produce multiple cavities in one or more workpieces. A standard power supply usually has one wire lead connected to the electrode or workpiece, through which the total power is available.

N [ Words starting with N ]
No-Wear	Defined by POCO as a condition under which 1 unit or less of electrode is eroded to every 100 units of workpiece. (one percent or less)
No-Load Voltage	Same as open gap voltage.
Non-Directional Finish	An EDM finish is non-directional and has no specific direction to its surface pattern.

O [ Words starting with O ]
Off-Time	The time between sparks, measured in microseconds. Too short an off-time may result in unstable machining or worse, DC arcing.
Ohm	A unit of electrical resistance equal to that of a conductor in which a current of one ampere is produced by a potential of one volt.
Oil-through-chuck	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.
Open Circuit	An electrical circuit which is not complete.
Open Gap Voltage	The voltage that can be read across the electrode/workpiece gap before the spark begins to flow. See gap voltage.
Operating Current	Same as average current.
Output	The voltage and current of an EDM power supply.
Overburn	Same as overcut.
Overcut	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 is called the 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 often used.
Overcut, per side	One-half of the Diametral overcut value. It is important to follow this procedure in designing electrodes: (1) Select surface finish settings 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.
Overlap	(1) The area by which the electrode for the next cut exceeds the workpiece cavity. (2) The difference between the rough machined hole or cavity size and the size of the electrode to be used for the next cut.

P [ Words starting with P ]
Particle Size	The average cross section of the solid graphite particles in a graphite system. The carbonaceous material from which the graphite is produced and the method of manufacturing determine the particle size. Also referred to as grain size.
Pause	The absence of electrical energy for a preset time following a discharge of electrical energy (pulse).
Pause Duration (time)	Same as off-time.
Peak Current	The maximum current available from each pulse from the power supply/generator.
Percent Electrode Wear	The volume of electrode worn away as compared to the volume of workpiece worn away.
Pieced Electrode	(1) An EDM electrode made using lower quality graphite as a base material with a higher quality material as the cutting surface. Such electrodes require careful mating to insure conductivity and correct positioning. (2) An electrode that has been repaired by replacing a broken part. All cutting surfaces must be of the same material for uniform performance. (3) An electrode made from several pieces of the same quality material to obtain a bigger electrode.
Plasma	A superheated, ionized gas that forms in the discharged channel due to the action of the thermoelectric force.
Platen	A large flat mounting surface affixed to the end of the quill or the ram of an EDM machine, and on which the electrodes or various electrode-holding devices can be mounted. It usually has tapped holes or machined T-slots for convenience in clamping electrodes or holders.
Polarity	In EDM, the designation of positive or negative electrical polarity of the electrode. Positive polarity of the electrode (in CNC EDM) is considered to be Normal and produces the least amount of electrode wear.
Potential	The difference in voltage between two points of an electrical circuit.
Power Supply	Or Generator. The part of the EDM system that supplies the voltage and current that causes the sparks or discharges between the electrode and workpiece.
Premium Graphite	A material with a particle size of 5 microns or less.
Pressure Flush	The forcing of dielectric up through flush holes in the workpiece or down through flush holes in the electrode.
Pretensioned Axis Screws	The practice of stretching a ball lead screw by several tenths (0.0001"), between two supports in order to provide added rigidity, alignment and accuracy.
Pulsator	A unit on the EDM machine which periodically causes the electrode to retract for a short period of time to aid in flushing a deep or blind cavity. Also commonly called a RAM cycler or jump control.
Pulse	The discharge of a single spark of electrical current having preset time.
Pulse duration (time)	Same as on-time.

Q [ Words starting with Q ]
Quench	The rapid cooling of the EDM'd surface by the dielectric fluid. Partially responsible for the metallurgical changes forming the recast layer and the heat-affected zone.
Quill	The moving member of an EDM machine on which the electrode or electrode holder is mounted. A cylinder working in a bearing or bushing.

R [ Words starting with R ]
Ram	The moving member of an EDM machine on which the electrode or electrode holder is mounted. A dovetail guided arrangement.
Ram Cycler	Same as pulser.
RC or Relaxation Circuit	An EDM power supply (circa 1962) that used capacitors to produce a spark. This early EDM power system is seldom used in advanced machines.
Recast layer	A layer created by molten metal solidifying on the workmetal surface.
Reverse Burning	The technique of mounting the electrode on the machine table or flush tank and the workpiece on the quill. Used in EDMing a blanking punch with female electrode.
Rotating Spindle	Either an accessory mounted on the quill or ram, or a built-in machine spindle used to rotate the electrode to achieve more uniform wear and to improve flushing conditions. Its use is limited to round electrodes. Another use for the rotating spindle is in trimming the workpiece with an indicator, as you would on a jig borer, for setting locations.
Roughing	The mode of EDM that removes the most material in the shortest time.

S [ Words starting with S ]
Secondary Discharge	A discharge that occurs as conductive particles are carried up the side of the electrode by the dielectric fluid.
Servo Mechanism	The device that drives and controls the movement of the quill or Ram.
Servo Reaction Time	The time between a signal to the servo and its physical response to the signal.
Side wear	In EDM, the wear along the sidewalls of the electrode.
Silicone	A dielectric fluid for special situations consisting mostly of the chemical polymer silicone.
Silver tungsten	A porous tungsten material which is infiltrated with silver.
Solid state power supply	Transistorized circuitry. See transistor.
Spark	An electrical discharge between two conductors.
Spark Erosion	Another name for EDM.
Spark gap	The distance between the electrode and the workpiece when discharges are occurring.
Spark intensity	The amount of energy in the spark.
Spindle	An upper rotating member of an EDM machine to which the electrode or electrode holder is mounted.
Split electrode	Multiple electrodes on a single machine electrically insulated from each other. Used with multiple lead power supplies.
Split lead power supply	Same as multiple lead power supply.
Square wave	A term for an electrical wave shape generated by a solid state power supply.
Stability	Refers to the steadiness of EDM cut. The opposite of hunting.
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.
Stroke	The distance the ram/quill travels under servo control.
Sublime	To pass directly from a solid state to a gaseous state. Graphite does not melt when heated at normal pressures, but passes directly into a gaseous state.
Suction Flushing	Using a vacuum to draw the contaminated dielectric away from the gap as opposed to forcing it out with pressure.
Superfine	A class of EDM electrode materials with a particle size from 6m to 10m characterized by moderately high strengths, usually isotropic.
Surface Finish	The surface roughness of a machined surface. µinRa in the U.S. µmRmax or µmRy in Asia µmRa or VDI in Europe.
Surface Integrity	The quality of the machined surface and subsurface and has little to do with surface finish.
Surface Flushing	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.
Surface Roughness	Surface irregularities on a machined surface. See finish, surface finish.
Swarf	The eroded particles or residue.
Synthetic Dielectric	Newer types of dielectric oils that are safer than mineral seal oils used.

T [ Words starting with T ]
Taper	The dimensional difference between the entrance and exit opening of a cavity, or between the entrance and bottom of a blind hole.
Tellurium Copper	An alloy of copper and tellurium.
Thermal Convectiona	Temperature Cut-Off A circuit that shuts down a system at a preset temperature. Used on EDM dielectric systems.
Through-Hole Flushing	The use of a pre-drilled hole in the workplace to inject dielectric fluid up toward the gap by injection flushing or down from the gap by suction flushing.
Total Form Machining (TFM)	An abrasive machining device capable of copying complete graphite electrodes.
Tramming Attachment	A mechanical accessory used in EDM to check the accuracy of the setup and to aid in the precise location of the workpiece in respect to the electrode.
Transistor	An electronic component used as a switch to open and close with extreme speed. Replaced the vacuum tube due to its reliability, long life, and much higher switching speed.
Trepanning Electrode	A hollowed out or tubular electrode which is used in through-hole machining to remove a large amount of material from the solid so as to avoid pre-machining by conventional means.
Tungsten	A metal used in pure or near pure state as an electrode material. Melting point is 3380ºC.

U [ Words starting with U ]
Ultrafine	A class of EDM graphite characterized by a particle size from 1µ to 5µ isotropy, uniform structure, and high strength.
Unstable	Erratic or intermittent EDMing.

V [ Words starting with V ]
Vacuum Flushing	Same as suction flushing.
Vacuum Tube Power Supply	An EDM power supply which uses vacuum tubes to switch the electrical machining pulses (sparks) on and off.
Vibrator	An accessory used on an EDM machine to move the workpiece or electrode back and forth rapidly. Employed primarily for improving flushing in blind cavities.
Viscosity	The tendency of a fluid to resist flow. High viscosity liquids are thicker.
Voltmeter	An instrument that measures the Average voltage across the spark gap on an EDM machine during machining.
Volumetric Wear	The total wear of the electrode expressed in cubic inches.

W [ Words starting with W ]
Wave Form	A geometric shape that represents the output of a power supply as seen on an oscilloscope.
Wear	The erosion of the electrode during the EDM process.
Wear Ratio	The ratio of electrode material volume worn away as compared to the volume of workpiece material removed by EDM.
Wire EDM	The electrode is a continuously spooling conducting wire that moves in preset patterns around the workpiece.
Working Gap Voltage	See gap voltage.
Workpiece	The part being (EDM) machined by a machine tool.

X [ Words starting with X ]
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Y [ Words starting with Y ]
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Z [ Words starting with Z ]
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