Electro Arc

Tag electrical discharge machining

Your Guide to EDM Terminology

EDM has become a common method used across industries with a number of sub-categories including MDM.  This list of EDM terms can help you understand all of the aspects of EDM.  Many of these terms are interchangeable with MDM terms:

Ammeter (Amp Meter) – A measuring instrument for electrical current.

Amp (amperage) applied – Amperage selected on power supply controls.

Amp (amperage) average – Amperage shown on the amp meter.

Arc (Arcing) A damaging flow of electricity (pulsating yellow flash) between electrode and workpiece.
Incorrect term for EDM machining (sparking).

Average current – (see average amp)

Blind Hole (cavity) – A cavity with no flush holes.

Burning – A synonym for EDM Machining.

Capacitor – An electrical component that stores a charge.  Used occasionally to intensify the spark.  (Wear on Electrodes will result).

Carbon – The raw material used to make graphite.

Center Flushing – Flush hole through the center of electrode..

Conductor – A material which will carry electric current.

Coolant – See dielectric.

Copper Graphite – Graphite infiltrated with copper.

Copper Tungsten – A blend of copper and tungsten.

Core – A non-machined area of the cavity created by the flush hole(s) in the electrode.

Corner Wear – Wear on the corners of the electrode parallel to the direction of machining, and proportional to the distance machined.

Crater – Small cavities in the workpiece created by the individual sparks.

Cut – Synonym for machining with the EDM process.

DC Arcing – see arc.

Deionization – Bringing the sparkgap back to a nonconductive state.

Depth finder – An electronic circuit which automatically stops the electrode .0001″ before it touches the workpiece without the high voltage on.  Used during “setup” for setting an accurate depth.

Dielectric – A fluid which insulates the sparkgap between the electrode and the workpiece until a high voltage ionizes the sparkgap and makes it a conductor.


Dither – See vibrator

Discharge – see spark

Dual powersupply – Two identical power supplies in one single cabinet, used to inform the operator when the electrode makes contact with the workpiece, usually with light or an acoustic signal.

Duty Cycle -“on time” +”off time”


EDM Grinding – This procedure is accomplished by mounting a rotating electrode wheel parallel to the direction of the servo.

Electrode – The “cutting tool” in the EDM process, always made of a conducting material.

End Wear – The linear wear at the end of an electrode after EDM machining.

Flashpoint – The temperature at which a flammable material will ignite.  An important factor in selecting a dielectric. 

Filtering – Removing the solid particles created during the machining from dielectric.

Flushing – The single most important Factor in EDM machining.

Flush Hole – A hole to facilitate flushing through either the electrode or workpiece.

Flush Pressure – The necessary pressure to insure an even flow over the “area of contact” between the electrode and the workpiece.

Flush Tank – Also called flush plate or flush pot, a box-like fixture mounted on the worktable. The flush hose connects to the side of the box and the workpiece is clamped either directly or on a subplate, on top, allowing the workpiece and into the empty space of the box.

Gap (spark gap)  – The distance between the electrode and the workpiece during machining.

Gap Voltage – The average voltage in the sparkgap during machining. (meter reading).

Frequency – The number of discharges (sparks) per second.

Graphite – An easy machineable electrode material with high heat resistance and good electric current transfer.

HAZ (heat affected zone) – Also called the “recast layer”.  The depth of the heat penetration altering the parent material’s metallurgical structure due to the EDM process.  Magnitude usually from .0002″ to .008″ depending on the material and the energy per pulse.

Hunting – Excessive reciprocating movement of the servo during machining caused by shorts in the stopgap.

Injection flushing – A synonym for pressure flushing.

Ionization – A breakdown of the resistance in the dielectric flowing in the sparkgap, when a voltage of sufficient magnitude is applied between electrode and workpiece.

Ionization Channel- The path of the positive and negative ions linking the electrode and the workpiece at the moment of ionization.

Microsecond – One-millionth of a second (.000001 seconds) (usec).

Multilead–One power supply with multiple independent power leads.

Nanosecond – One billionth of a second (.000000001 seconds)

Non-directional – A finish having no specific direction to its surface pattern.

Normal Polarity – Negative polarity.  A designation no longer used, as the polarity depend on the application, and as such a polarity (positive or negative) can only be normal in relation to a given application.

No Wear – No wear as such does not exist, but generally speaking, wear less than one percent is called “no wear”  range, a deposit or plating can occur so the electrode actually grows, but as this phenomenon is unpredictable it has no practical value.

Oil through Chuck – A sealed adjustable chuck for tubular electrodes which allows a flow of dielectric fluid through the chuck to the electrode.

“On Time” – Duration of the applied amperage during one pulse cycle measured in nanoseconds.

“Off Time” – The time in microsets between the applications of open gap voltage.

Overcut – The dimension the finished cavity is larger than the electrode. (2 x sparkgap).

Redressing – Removing the worn part of an electrode, bringing it back to its original shape.

Recast Layer – See HAZ.

Reverse Polarity – see normal polarity.

Servo – The electro-mechanical mechanism which automatically maintains the proper spark gap during machining.

Spark -controlled discharge between electrode and workpiece.

Sparkgap – The distance between the electrode and workpiece during machining.

Spark Erosion – Synonym for EDM.  Mainly used outside the U.S.

Split Lead – See Multi lead.

Stepped Electrode – An Electrode constructed in two or more concentric tiers, to be used for through-hole machining,  The first smaller portion is used for the roughing, and the larger subsequent tiers are used for the medium to finishing machining.

Trepanning Electrode -An electrode constructed like a cookie cutter.  Used to machine through holes, this way increases the machining speed by minimizing the amount of workpiece material to remove.

What is the History of Electro Arc and EDM?

When you search for the term “metal disintegrator” you will likely find ‘Electrical discharge machining’ as a result.  That is because the technological breakthrough that led to metal disintegrating machines was spearheaded by a team including Harold Stark who went on to patent the idea for AC metal disintegrators and started the world’s first metal disintegration machine factory in Detroit Michigan.  This process is metal disintegration machining (MDM).

You may have heard Electrical discharge machining, EDM for short, called spark machining, arc machining, and spark eroding.  This is a non-conventional group of machining which now includes electrochemical machining, water jet cutting, and laser cutting.  This process is limited to use with ferrous alloys because it requires the base material to be electrically conductive.  A solution for high-accuracy, complex machining applications provides an efficient alternative where other methods are impossible.  Using an electrical current, spark discharge erodes the workpiece using dielectric fluid as an electrical insulator. There are three main forms of EDM, wire EDM, die sinker EDM, and hole popping EDM.  

EDM is usually associated with the wire EDM machine method which was developed between the 1960s and 70s to make dies from hardened steel.  This EDM process uses wire wound between two spools of wire creating two electrodes, the tool-electrode, and workpiece-electrode, which are separated by dielectric fluid. With increased voltage, the fluid produces an electric arc. The wire moves in a controlled pattern and sparking occurs between the wire and the workpiece.  This method removes excess material with automated technology similar to CNC providing high accuracy and precision.  Commercial wire EDM capability has continued to advance substantially over the last few decades.

Joseph Priestly originally discovered the erosive effect of electrical discharges in 1770.  Die sinker EDM was invented independently by two groups.  In 1943 two Russian scientists Boris and Natalya Lazarenko were exploring methods to increase the lifespan of tungsten breaker points. Their research led to the discovery that erosion could be precisely controlled if the electrodes were immersed in dielectric fluid. This allowed the invention of an EDM machine tool for processing hard materials like Tungsten. This tool became known as a resistor-capacitor (R-C) circuit for EDM.  

During this time, without knowledge of the experimentation taking place in Russia, a team of American scientists consisting of Harold Stark (the founding president of Electro Arc), Victor Harding and Jack Beaver were also developing a method to remove broken drills and taps from aluminum castings.  This team was tasked by their employer with finding a solution because tools were being broken off in expensive aircraft parts.  Initially constructing machines from electric etching tools, they were unsuccessful.  After trying compressed air, they added fluid to the machines, combined with spark repetition allowing them to cut through metal quickly and efficiently while the coolant flushed away metal particles created in this process. Their research was able to produce 60 sparks per second, a breakthrough in technology at the time. Machines initially developed by this team were used during World war II and the trio patented the system for removing broken bolts, taps, and drills as well as an electronic-circuit servo system that maintained proper spacing between the electrode and the workpiece.

This led Harold Stark to develop Electro Arc’s Metal Disintegrator line of metal disintegrating machines which are still produced by Stillion Industries today (Stillion Industries purchased Electro Arc in 2019).  This technology was key in the development of vacuum tube EDM machine tools capable of producing thousands of sparks per second (electric discharge machining) in the 1960s.  Die sinker EDM machines are traditionally used to create three-dimensional shapes.  EDM provides an advantage because the process is predictable and accurate, making it easy to reproduce, but it is slower than other methods.

Hole drilling EDM is a specialized hole-making machine sometimes called a “hole popper” which is used to create the pilot hole necessary for wire threading. Using thermal energy rather than mechanical force, these machines cut through extremely hard materials such as titanium, carbide, carbon graphite, and high alloy steel.  These machines work on the same principle as wire EDM machines.  Instead of wire, these machines use a tool that works like a drill bit, no physical contact takes place between the tool and the workpiece, the electrical discharge is conducted to rapidly cut the metal.  This process is ideal for extremely small holes, as small as 0.010”. 

In his book, ‘Electrical Discharge Machining’ Elman C. Jameson mentions working with Victor Harding and Harold Stark during the origination of the EDM process in the United States.  EDM became popular in Japan as a result of damage from the war.  This new method was key in rebuilding after the destruction of their infrastructure.  On the other hand, The existing equipment and workers in the US caused a delay in the acceptance of EDM technology in the US.  Electro Arc metal disintegrators are an appealing option because they do not require special training for operators as other EDM machines require.

What is the Spark Erosion Process?

Imagine you’re on the production line working on a large manufacturing machine. Everything seems to be running smoothly, until crack, a tap has broken off in the machine. A person breaks the tap, not the machine.

Unable to retrieve the broken piece without damaging the machine or stripping the threads of the casting, you are left with two options. You can replace the broken machinery, which comes at a high cost and slows productivity, or you can apply spark erosion, solving your problem in seconds rather than hours or days and for a quarter of the cost.

Spark erosion, metal disintegration, electrical discharge machining; if you work in any industry that utilizes machinery you’ve probably heard one or more of these terms. Each of these titles is used to explain the process of removing metal using electric currents under carefully controlled conditions.

How does the spark erosion process work?

While (EDM) spark erosion can be used to create specific metal parts, it is also commonly used to remove broken drill bits, taps, bolts, and studs from within a machine casting without damaging the threads or casting itself. This is called MDM.

Spark erosion is conducted through metal disintegration machines (EDM). These machines use electrodes to send low voltage/ high current electrical charges that melts the designated piece of metal at the same time cold water thermal shocks the molten steel and pulverizes it into micro-size pieces and flushes it away.

Because there is no direct contact between the electrodes and the machine casting, spark erosion allows you to work with even the most intricate sections and weak materials without risking distortion. It is this precision that makes spark erosion the most effective way to salvage parts that would otherwise be deemed unusable.

Five steps to applying spark erosion

Step 1: Get your metal disintegration machine ready. Electro Arc has a variety of options to choose from depending on your need, including portable, table top, and specialized metal disintegrators.  Use our new Machine Builder if you are not sure which machine is best for your application.

Step 2: If you are using a portable machine, attach the provided portable electrode head to your drill press, CNC machine, lath, or any type of machine tool.

Step 3: Align the electrode to ensure it’s centered over the object you plan to remove and lower the splash bag.  Verify that the bolts are tight. Each machine comes with a splashguard mechanism for safety purposes in order to keep sparks contained and prevent eroded metal from flying.

Step 4: Switch on the power supply. Portable metal disintegrators come with a small, rolling power supply cabinet that is easily transportable. The power supply features a built-in coolant tank and heat selector knob. For easy usability, all machines come with a chart that directs you on exactly which heat setting to use for each size broken tap or drill that you’re planning to remove.

Step 5: Turn the heat selector knob to the desired temperature and begin the process. Within seconds, the MDM machine will finish its cut. You can then clear the hole of any remaining debris using the provided air compression tool and see that your part has been completely recovered, casting, and threads left unscathed.

Yo can see the Electro Arc process in action, with video tutorials and case studies on Electro Arc’s YouTube Channel.  Since Stillion Industries purchased Electro Arc in 2019, we have created a new channel with updated videos as well.

Advantages of using spark erosion machines

In a previous blog post, we discussed the many benefits of using Electro Arc’s spark erosion machines, some of which include:

  •      Simple operation
  •      Unbeatable price
  •      Relatively lightweight and easy to maneuver
  •      Quick setup and breakdown
  •      Easily manageable for one person
  •      Little-to-no maintenance; simply keep it filled with fresh coolant

Spark erosion is the fastest and most cost-effective solution to recovering machinery that has been compromised by broken tools. For 75 years, Electro Arc has been perfecting this process and supplying premium metal disintegrators at affordable prices throughout the world.

You can see lots of broken bolt removal examples which illustrate how an Electro Arc metal disintegrator will benefit your company and save you money.

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