Help Needed: Basics of EDM Technology

If by EDM you mean Electrical Discharge Machining I can help you. The term refers to a group of techniques in general and one in particular. The full term as you stated it refers to machining conductive metals with a shaped electrode. This is done while the workpiece is flooded with a dielectric fluid. A rapidly chopped electric current is passed through the fluid and causes controlled spark erosion of the workpiece. Two forms are used. For diesinking, a carbon electrode that is cheap and easily shaped is used. However it cannot be used for production machining since it wears too rapidly. Carbon electrodes are used for short run work like die and mold sinking. For longer run production work a shaped tungsten copper alloy electrode is used. It is much more difficult to make and more expensive, but it will last for a long enough time to do medium run production work. Another variation of this technology is Wire EDM in which a spool of wire is continously fed through a metal part flooded with deionized water and guided by a computer. It works somewhat like an electrical discharge version of a jig saw, but very accurately. This is used to make most of the components of a punch press die since the same program elements can be used to insure an almost perfect match between the shapes of the die, perf plate, stripper, and any other components that require a good match. Tolerances in 1/10ths of a thousandth of an inch are regularly held with this method. Electrochemical grinding is a process that uses a conductive wheel shaped like the ground surface and is slowly passed across the work while the electrical discharge and the electrochemical action do their work. This works a little like creep grinding except that an electrical discharge action is added to the process. the last one I am familiar with is the broken drill and tap removal machine. It uses a hollow electrode sized for the drill or tap and is meant to blast through the core of a drill or tap broken off in a hole in an expensive part. The dielectric fluid is fed through the hollow electrode and a mechanical vibrator is used to break up the contact and create sparks. Done right, it is then possible to fish out the flutes of the broken tool and salvage the part. I hope this helps you.