Electro Arc

Difference between MDM and EDM

Metal Disintegrators or MDM machines are manufactured for the specific purpose of removing broken tools from workpieces. The metal disintegration process removes a tap, bolt, or drill leaving the hole intact and allowing a part to be reclaimed.

Electrical discharge machines are also known as an EDM machine which uses non-conductive fluid with an electrode to remove metal. This may be accomplished with wire, hole or sinker EDM depending on the application. These machines vaporize the metal and remove it with the help of fluid.

The difference between MDM and EDM is speed, cost, and accuracy. MDM removes material very fast. Using a spark erosion process MDM is commonly used for destructive cutting. Typical application includes broken tool extraction (taps, drills, reamers, drill bits) metallurgical sample excavation, and bolt removal. MDM is the fastest, most efficient, and most cost-effective method to remove broken tools, studs, or fasteners.  

Using EDM to remove broken tooling is possible, but it is time-consuming and has limitations. First, the part has to be small enough to fit in the dielectric fluid container. Second, an EDM machine will take hours to extract a 3/8” tap, whereas an MDM will take just minutes. Third, the MDM process does not require submersion of the part. Lastly, EDM machines are significantly more expensive than MDMs, and tying up an expensive production machine with tooling extraction could be costly.  Electrical discharge machining (EDM), also known as spark machiningspark erodingdie sinkingwire burning, or wire erosion, is a manufacturing process whereby a desired shape is obtained by using electrical discharges (sparks). Material is removed from the workpiece by a series of rapidly recurring current discharges between two electrodes, separated by a dielectric liquid and subject to an electric voltage. One of the electrodes is called the tool-electrode, or simply the “tool” or “electrode,” while the other is called the workpiece-electrode, or “work-piece.” The process depends upon the tool and workpiece not making actual contact.  When the voltage between the two electrodes is increased, the intensity of the electric field in the volume between the electrodes becomes greater than the strength of the dielectric (at least in some places), which breaks down, allowing current to flow between the two electrodes. This phenomenon is the same as the breakdown of a capacitor (condenser) (see also breakdown voltage). As a result, the material is removed from the electrodes. Once the current stops (or is stopped, depending on the type of generator), the new liquid dielectric is usually conveyed into the inter-electrode volume, enabling the solid particles (debris) to be carried away and the insulating properties of the dielectric to be restored. Adding new liquid dielectric in the inter-electrode volume is commonly referred to as “flushing.” Also, after a current flow, the difference of potential between the electrodes is restored to what it was before the breakdown so that a new liquid dielectric breakdown can occur.

A Trek 760 bike owner faced the conundrum of having a shifter screw broken off in the braze-on and asked for advice on a biking forum, one suggestion was to use electric discharge erosion to remove it.  Applications for MDM are far and wide, from the smallest project to the largest machinery.

Click here to view even more info on the terminology used in metal disintegration machining.

Electro Arc