How shall we call EDM?

Modern Machine Shop, Feb, 1992 by Mark Albert

Electrical discharge machining. Spark erosion. Eloxing (from ELOX, one of the earliest companies to build EDM equipment and one that continues its pioneering tradition to this day). Sometimes the term tap busting is heard in conversations about EDM. But the acronym EDM is almost universally recognized and accepted today.

Things aren't quite so settled with the names for the two types of EDM. For the one type, it's traveling wire EDM, wirecut EDM, or wire EDM. As an editor, I prefer wire EDM as the common designation for the process that uses an electrically charged wire moving from reel to reel to cut a narrow kerf as it follows a preprogrammed path through a workpiece.

The situation is even worse with the other type of EDM, in which electrical energy emanating from a shaped piece of material, usually copper or graphite, forms a like-shaped cavity in the workpiece. You'll hear it referred to as conventional or standard EDM, ram or ram-type EDM, vertical EDM, die sinking, sinker EDM. I likek ram EDM best because it's short, simple, and direct. It matches the term wire EDM. "The two types of EDM are wire and ram."

One user who has strong feelings about names for the respective types of EDM is Milt Thomas, president of Wire Cut Company, Inc., a prosperous job shop in Buena Park, California. Mr. Thomas's shop has been particularly aggressive about applying both types of EDM in production jobs, including aerospace work involving intricate workpieces of exotic materials.

He argues strongly for standardizing our EDM terminology. If everyone uses the same terms with agreed-upon meanings, there will be less confusion and better communication in the industry. I say Amen to that. EDM, even after all these years, still suffers from an image problem. It is frequently lumped in the "nontraditional" category of machining processes, as if EDM is an experimental or uncertain process, at the fringes of metalworking. Muddled names for EDM processes hardly counteracts this false impression.

Mr. Thomas makes a very insightful and compelling point. What makes the two types of eDM different from each other is precisely and uniquely the form of electrode they use. Therefore, he contends, the standard names for each type

should properly be based on this distinction. He proposes calling the one type of EDM "wire EDM" and the othertype "solid electrode EDM." (Solid implies that the electrode has length, breadth, and thickness.)

Both types are changing as advances in power supplies, control units, machine design, electrode materials, filters, and so on, make EDM the first choice, or even the only choice, for a growing body of applications. Yet, as Mr. Thomas points out, none of these developments has altered the essential difference between the form of electrode used in the two types of EDM.

I cannot disagree with Mr. Thomas's thinking. Unfortunately, his proposed solution isn't entirely satisfactory, despite its logic and precision. The respective terms are not perfectly parallel or mutually exclusive. A wire electrode is not "non-solid" in contrast to the electrodes used in the other type of EDM, for example. And what about EDM units especially designed for making small holes? Many of them use a wire or very slender tube that feeds ram-like into the workpiece, a hybrid process of sorts.

But I don't mean to quibble. Mr. Thomas takes EDM very seriously. He's built a highly successful business dedicated to, and made possible by, this technology. He's witnessed the technology mature rapidly since the 1960s and he is excited about the 1990s as a new era for dramatic growth in EDM.

Perhaps we will adopt standardized names for the two types of EDM. Perhaps not. Either way, EDM remains one of the most innovative and dynamic technologies in metalworking today. Whatever terms we use, we'll all be talking more about EDM.