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 which can be read across the electrode/workpiece gap before the spark current begins to flow. See Gap voltage.
Operating current - Same as Average current.
Oscilloscope - An electronic imaging device which can be used to visually check the shape and voltages of pulses being generated by the EDM power supply.
Output - The voltage and current of an EDM power supply.
Overburn - Same as Overcut (below).
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 (or hole) 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.
Particle size - The average cross section of the solid graphite particles in a graphite system. The particle size is determined by the carbonaceous material from which the graphite is produced and the method of manufacturing. 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 a 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 which 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 potential to the electrode.
Pore - EDM graphite is made of individual particles bonded together. This leaves voids or spaces between them, called pores. Larger particles mean larger pores, or spaces, between them. No graphite may be machined to tolerances closer than its average pore size.
Potential - The difference in voltage between two points of an electrical circuit.
Power pack - Same as Power supply (below).
Power supply - The part of the EDM system that supplies the voltage and current that causes the sparks or discharges between the electrode and workpiece. It is usually housed in a cabinet separate from the machine tool and connected to it by a cable.
Pressure flush - The forcing of dielectric up through flush holes in the workpiece or down through flush holes in the electrode.
Premium graphite - A material with a particle size of 5 microns or less.
Pulsator - Not related to the generation of sparks. It is a unit added to, or built into, an 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.
Pulse - The discharge of a quantity of electrical energy having preset voltage and amperage and expended over a preset time.
Pulse duration (time) - Same as On-time.
Pulse timer - This refers to the spark, not flushing. Used to set the length of on-time and off-time of the spark. On some machines, on-time and off-time can be set individually in microseconds.
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.
Quench - The rapid cooling of the EDMed 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.
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 Pulsator.
RC (relaxation) circuit - An outmoded EDM power supply circuit which uses capacitors to store the charge that produces the spark at the gap. The capacitor is charged through a resistor and discharged across the gap when conditions are correct (gap distance, voltage, etc.). This is the original EDM circuit and is seldom used in advanced machines.
Recast layer - A layer created by molten metal solidifying on the workmetal surface.
Reciprocator - A hydraulic device attached to the ram of conventional EDM providing a longitudinal reciprocating action.
Rectifier - This converts alternating current to direct current.
Refeed - Automatic electrode replenishment.
Relaxation circuit - Same as RC circuit (above).
Repetition rate - Same as Frequency.
Resolidified layer - Same as Recast layer (above).
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.
Reverse polarity - A term used to indicate positive polarity on some machines.
RMS (Root Mean Square) - An obsolete term used in surface finish measurement.
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 (hogging) cut - The mode of EDM that removes the most material in the shortest time.
Safety cut - The method of undersizing roughing electrodes to compensate for differences between them and the finishing electrodes.
Secondary discharge - A discharge that occurs as conductive particles are carried up the side of the electrode by the dielectric fluid.
Sensitivity - A control switch that adjusts the response time of the servo mechanism.
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 side walls 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.
Slurry - A watery mixture of insoluble material and water. Used as an abrasive in ultrasonic machining.
Solid state power supply - Transistorized circuitry. See Transistor.
Sonotrode - The forming tool in ultrasonic machining.
Spark - An electrical discharge of very short duration between two conductors.
Spark erosion - Another name for EDM. Used primarily outside the U.S.
Spark gap - The distance between the electrode and the workpiece when discharges are occurring.
Spark generator - Same as Power supply.
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 relative roughness or smoothness of the machined surface. Usually measured in µin Ra in the U.S.
Surface integrity - The quality of the machined surface and subsurface.
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.
Tap buster - Same as Disintegrator.
Tap - A control on some early power supplies that changes spark frequency and on-time.
Taper - The dimensional difference between the .entrance and exit opening of a through-hole cavity, or between the entrance and bottom of a blind hole.
Tapping attachment - An accessory that holds and rotates an electrode as it EDMs a threaded hole into a workpiece. It advances the electrode to produce the pitch of the thread desired.
Tellurium copper - An alloy of copper and tellurium.
Temperature cut-off - The dielectric oil temperature at which the power is shut off.
Thermoelectric - The combined action of heat and electricity.
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.
Tilting head - An attachment allowing the electrode to be tilted in two directions.
Timed retractor - Same as pulsator.
Timer, timing unit - A control unit that establishes the spark on- and off-times.
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.
Transducer - A device for changing electromagnetic force into mechanical force. A loudspeaker is a transducer. In EDM, a transducer is used in ultrasonic machining of graphite, though the sound produced is too high for most human hearing.
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.
Tubular electrode - A round electrode with a center hole.
Tungsten - A metal used in pure or near pure state as an electrode material. Melting point is 3380ºC.
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.
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 voltage. On an EDM machine, it measures the voltage across the gap.
Volumetric wear - The total wear of the electrode expressed in cubic inches.
Wave form - A geometric display of the output of a power supply as seen on an oscilloscope.
Wear - The erosion of the electrode during the EDM process.
Wear ratio - The volume of electrode worn away as compared to the volume of workpiece material removed by EDM.
Wire EDM, wirecut - The electrode is a continuously spooling conducting wire that moves in preset patterns around the workpiece.
Working gap voltage - See Gap voltage.
Workpiece - Any part on which EDM is being used to cut holes or cavities.