What is EDM and why is it so @#$! expensive?

We hear it all the time... "I know I need the results I get with EDM but have never understood...what is it and why does it cost so much?"
EDM is an acronym for Electrical Discharge Machining and is a method of removing material from an electrically conductive material, some type of metal generally, by means of non-contact electrical current.
"Oh that really clears it up!"
Ok, so it isn't so easy to explain or understand but it works and helps us all to achieve part designs that sometimes just cannot be made any other way.
And to further confuse you, there are two types of EDM processes that you will generally hear referred to as Ram and Wire EDM.
Ram type EDM uses an electrically conductive graphite electrode, machined to the desired shape by traditional methods, to form the shape in the part.
Wire EDM uses a very fine wire, strung taunt between two points like a jig saw blade, that is maneuvered thru a part to cut the desired shape.

How is EDM more beneficial than traditional metal removal methods such as milling or turning?

EDM is precise. Depending on whom you ask, traditional machining methods can reliably produce parts to tolerances of .001 inch. EDM can easily achieve tolerances in the tenths of thousanths(.0001) of an inch.
Parts that have already been hardened and cannot be machined with tradional methods, can be shaped using electrical discharge machining.
It induces no physical stresses on the part, so it doesn't change the part shape or introduce stress points. This makes it an excellent process for parts that have already had other finishing processes like grinding completed on them.
Shapes than cannot be created by other means can be done with EDM. An example would be holes with square corners or pockets with square corners at the sides and bottom.

How is EDM less beneficial than tradtional methods?

It is a slow process which means it is an expensive process! It is easy to assume that a hole made by EDM can be done as quickly as traditional drilling of the same hole and this simply isn't the case. In fact, even if you pre-drill the hole (a good cost saving method), a hole will still take many times longer to EDM than drilling the same hole!
The benefits for the extra time and expense expended: precision, fine finish, ability to machine hardened and unusually shaped parts, and no deformation of the part.