Adron Medical EDM Electrical Discharge Machining

Why Use EDM?

Case Studies & EDM Glossary

EDM unlocks the potential to design parts for better function, without the restrictions of other metalworking processes.

Why EDM?

A) You Can't Always Identify an EDM Part By Its Looks

The parts to the left look like a milling job; however, Adron won a government prime contract for 3,500 pieces of this 7075-T6 aluminum back plate latch because our price was less than half the cost of milling. These latches are a general machine shape without close tolerances and are not subject to heat-treat distortion. They are an ideal production wire EDM job because the parts can be nested for optimum material use, stacked for faster cutting, and burr-free EDM production saves secondary costs.

B) Thin Stem Made this Simple Titanium Shape a Wire EDM Job

The obvious methods - stamping and laser cutting - were tried for this part. Wire EDM proved the most cost effective. Titanium earring shapes used by a jewelry artisan illustrate why wire EDM can be a better choice than more conventional machining methods. Although the earrings are simple shapes, the stem (which is ultimately bent to become the ear loop) is too thin to be stamped. EDM also was competitively priced with laser cutting and chemical etching, however these caused the stem to become brittle and break. The earrings were nested for optimum material use, stacked for faster cutting, and wirecut burr-free.

EDM Glossary

Abrasive Cutting Master (ACM) - The tool used in the total form machining method of producing graphite electrodes.

Altered Metal Zone (AMZ) - The mechanically and mechanically altered zones created by the EDM process on the workmetal surface.

Ammeter - An instrument for measuring electric current in amperes.

Amperage (A) - In EDM, the amount of average current measured during the cut.

Ampere - The unit of electric current. Equivalent to the steady current produced by 1m, volt across 1 ohm.

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

Anisotropic - Exhibiting properties whose values change when measured along differing axes. Opposite of isotropic.

Anode - The positive terminal of an electrolytic cell or battery. Often incorrectly applied to the tool (electrode) in the EDM process.

Arc - A continuous flow of electrical current between an electrode and workplace. 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.

Arc dampener - Same as Arc suppressor (below).

Arc guard - Same as Arc suppressor (below).

Arc suppressor - A circuit in the EDM power supply that reduces the possibility of arcing.

Automatic Tool Changer (ATC) - A device used with computer numerically controlled (CNC) EDM to provide automatic operation.

Automatic depth finder - (Refer first to Depth finder) An automatic depth finder is electrically connected to the servo and will stop the downward advance of the electrode at within 0.0001" of the workpiece surface and will hold it at this distance. Therefore, if the workpiece position is shifted by moving the table in any direction with its handwheels, the servo will constantly adjust the vertical relationship of the electrode to maintain its distance at 0.0001" away from even a previously EDMed cavity, even one with an irregular surface.

Average current - The average value of all the minimum and maximum peaks of amperage in the spark gap, as read on the ammeter. For any given available current setting, the higher the average current, the greater the efficiency of the particular cut being made. See Machining rate.

Billet - A block of graphite, usually the uncut 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 end of a through-hole cavity at the moment of completion.

Burning - A slang term for EDM.

Capacitor - An electrical component that stores an electric charge. In some EDM power supplies, a bank of capacitors are connected across the machining gap. The current for the spark comes directly from the capacitors when they are discharged.

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, the others being amorphous carbon (having no definite crystal structure), diamond, and the recently discovered fullerenes (also known as Buckyballs).

Catalyst - A material which 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 of graphite and metal which aid in establishing a current path in the dielectric fluid.

Cathode - The negative terminal in an electrolytic cell or battery. In EDM, sometimes incorrectly applied to the workpiece.

Center flow - The 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.

Circuit - A continuous path allowing and directing the flow of electric current.

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

Collet - A device used to hold electrodes with round shanks.

Colloidal suspension - Particles suspended in a liquid that are too fine to settle out. In EDM, the tiny particles produced in the sparking action form a colloidal suspension in the dielectric fluid.

Common metals - The first group of metallic electrode materials. Includes copper, brass, and zinc.

Composite - Made up of more than one material. 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.

Computer Numeric Control (CNC) - Programmed control of EDM by means of microprocessors.

Condenser - An obsolete term for capacitor.

Conductor - A material that will carry electric current.

Contamination - The accumulation of debris in the dielectric fluid, causing a decrease in the fluid's dielectric strength.

Coolant - Sometimes used incorrectly to describe dielectric fluid.

Copper graphite - A graphite EDM electrode material infiltrated with copper.

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.

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

Crater - The small cavities left on the EDMed surface of the workpiece by the EDM sparks. Also known as pits.

Cubic inches per hour (in3/hr) - The units of measure used to describe the rate of metal removal from the workpiece. See Machining rate.

Cut, take a cut - To machine with EDM.

Cutting rate - Same as Machining rate.

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.

Decalescent point - The highest temperature at which a tool steel may be heat treated and still be hardened in a quenching medium.

Deionization - A return of the condition of the dielectric to a non-conductive state. Failure to accomplish deionization (through flushing) during off-time of the spark is responsible for DC arcing.

Depth finder - An aid for machine set up. An electrical impulse is used to indicate when a downward moving electrode approaches to within 0.0001 of contact with the surface of the workpiece, either to start a cut or to reposition the electrode to resume cutting, as after dressing an electrode. Used when manually or power jogging an electrode downward. Usually used in conjunction with a dial indicator to set depth of cut at which EDMing will stop. NOTE: Do not confuse with Automatic depth finder.

Depth of craters, pits - The distance from the peaks to valleys on an EDMed 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.

Diameter (dia.) (Ø) - The length of a straight line through the center of a round object.

Diametral sparking distance - The difference between the electrode dimension and the dimension of the cavity produced.

Dielectric fluid - In EDM, a nonconductive liquid. It fills the gap between the electrode and workpiece 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 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.

Disintegrator - A different branch of EDM technology using the destructive power of electric arcs.

Dither - A slight up and down vibratory motion of the machine tool ram and attached electrode used to improve cutting stability.

Downfeed - A control circuit to advance or retract the electrode.

Dressing - The remachining of the face of a three dimensional electrode to sharpen its detail after it has been used to sink a mold cavity. Electrodes used to make a through-hole are often cut off at the worn end.

Dual power supply - Two EDM power supplies in a single cabinet which can be used to operate two machines simultaneously, or can be connected to apply the full power available to only one machine.

Ductile - Capable of being drawn out or hammered thin.

Duty cycle - The percentage of the on-time relative to the sum of the on-time and off-time setting for a particular cut.

Edge finder - An electrically activated device on an EDM machine to aid in the accurate location of the workpiece with respect to the electrode. When any point along the side of the workplace is brought to within approximately 0.0001" of any point along the side of the electrode, a signal light or buzzer will be activated.

EDM - See Electrical Discharge Machining (below).

Efficiency - A measure of EDM performance which varies with the on-time and off-time settings for an EDM cut. See Duty cycle (above).

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 Resistivity - 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 overcut that occurs.

Electrode growth - A plating action occurring at certain low wear settings which causes workpiece material to build up on the electrode, causing it to increase in size.

Electrode Management Technology (EMT) - Automatic methods of replenishment, redressing, and feeding of electrodes, especially in flexible machining applications.

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 EDMing. Can be given as a dimension, or as a percentage of the original usable length of the electrode.

Entrance opening - The point at which the electrode first enters the workpiece.

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 metallics used as EDM electrode materials. Includes all rarely used metals such as tantalum, nickel, molybdenum, etc.

Exudate - Material that has flowed or diffused out of a porous body.

Farad - The unit of electrical capacitance. Used to rate the energy storing capacity of a capacitor. One farad = the capacitance of a capacitor between whose plates there appears a potential of one volt when charged by one coulomb (ampere = one coulomb/sec.).

Filler - In manufactured carbon and graphite product technology, carbonaceous particles comprising the base aggregate in an unbaked green-mix formulation.

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

Fine - A class of EDM graphite characterized by a particle size range from 11m to 20m.

Finish - The surface texture produced by EDMing. Usually given in min Ra (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 finish desired.

Flashpoint - The temperature at which any flammable material will burst into flame. A factor in selecting dielectric fluid for EDM.

Flexural strength - A property of a solid material that indicates its ability to withstand a flexural or transverse load.

Fluid level 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 EDMing through-holes. Top and bottom surfaces must be precision ground parallel. 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 - Flowing dielectric through the gap to remove the debris caused by machining with EDM.

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

Flushing pressure - The pressure applied to the dielectric to force it through the spark gap.

Frequency - The number of cycles (on/off) completed per unit of time. Usually expressed in Hertz.

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 which can be read across the gap during the spark current discharge is the working gap voltage.

Generator - An old term for EDM power supply.

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 of 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.

Head - That part of the EDM machine tool in which the quill or ram 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 workmetal.

Hertz (Hz) - The international term for one complete electrical wave cycle. In EDM, the unit of frequency.

Hogging - Same as Roughing.

Hunting - An erratic bouncing movement of the quill of an EDM machine during a cut. Causes include 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 EDMed.

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 - Generally accepted as a phenomenon by which the dielectric between two points on the electrode and workpiece become electrically conductive. See Dielectric.

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.

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

Low wear - The result of certain settings for EDM machining which produces a very low degree of wear on the electrode. In some cases less than 1%, which is also known as no-wear.

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 - 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.

Microfarad - One-millionth of a farad. See Farad.

Micron, micrometer (m) - A unit of length equal to one-millionth of a meter.

Microinch (min) - One-millionth of an inch (0.000001").

Micro ohm (mW) - One-millionth of an ohm (0.000001 ohm).

Microprocessor - A computer-on-a-chip. Found in all advanced EDM systems, the microprocessors provide many control functions.

Microsecond (ms) - One-millionth of a second (0.000001 sec.).

Mil - One thousandth of an inch (0.001").

Millisecond (ms) - One thousandth of a second (0.001 sec.).

Miss - A pulse that does not produce machining due to too great a gap.

Modular construction - When used in EDM, a type of power supply where entire circuits are integrated on boards or modules. This type of construction provides a simple and rapid method of servicing and replacing electronic circuits in the field.

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.

Multiple lead (Multilead) power supply - A standard power supply usually has one wire lead which can be connected to the electrode or workpiece and through which the total power available can be channeled. With a multilead power supply, it is possible to divide the total power available into small units, each capable of being channeled through separate wire leads connected to multiple electrodes or workpieces for production work. Or, all power can be put through a single wire lead by connecting all the individual leads into one.

No-wear - Defined by POCO as a condition under which 1 unit or less of electrode is eroded to every 100 units of workpiece.

No-load - Same as Open gap voltage (below).

Non-directional finish - A finish having no specific direction to its surface pattern. An EDM finish is non-directional.

Normal polarity - Negative polarity to the electrode.

Off-time - The time between sparks, measured in microseconds. Too short an off-time may result in 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 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.