Difference between MDM and EDM

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

The difference between MDM and EDM is speed, cost and accuracy. MDM removes material very fast. MDM uses a spark erosion process commonly used for destructive cutting. Typical application includes broken tool extraction (taps, drills, reamers, drill bits) metallurgical sample excavation and bolt removal. There is no faster or efficient or cost effective method to remove broken tools, studs or fasteners than MDM.  

Using an 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, where 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 work piece 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 work piece 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.

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