Tracing sinker EDMing back to its original spark

Electrical discharge machining (EDMing) goes by many names—burning, spark machining, spark eroding, vaporizing—but they all refer to variations on the same process: removing material by running an electric current between an electrode and a negatively charged workpiece material submerged in a dielectric fluid. At least in the case of sinker EDMing, that’s pretty much all there is to it.

Current History

That may sound simple now, but it was a long time in coming. According to Stephen Krar and Arthur Gill’s book “Exploring Advanced Manufacturing Technologies,” the principle of electrical discharge erosion was discovered in 1770 by Joseph Priestley, an English physicist who is also credited with the discovery of oxygen, having isolated it in its gaseous state.

However, the EDM principle wasn’t fully harnessed until 1943, when Russian scientists B.R. Butinzky and N.I. Lazarenko set out to find ways of preventing the erosion of metal in electrical contacts. While they failed in that regard, their resistor-capacitor-powered machine was the initial foray into sinker EDMing.

Almost simultaneously, halfway around the world, U.S. scientists Harold Stark, Victor Harding and Jack Beaver were developing a machine to remove broken drills and taps from aluminum castings. Krar and Gill wrote that experiments with more-effective power sources, fluid replacement and electromagnetic circuit interrupters led to the creation of a vacuum-tube-powered design that could produce thousands of sparks per second—arguably making it the first recognizable sinker EDM.

Nearly 3 decades later, in 1970, EDM specialist ABET Industries Corp. opened its doors in LaGrange Park, Ill., located west of Chicago.

ABET Engineering Corp. was established in 1970 (above) and occupies the same facility in LaGrange Park, Ill., today (below). Image above courtesy ABET Engineering. Image below courtesy E. Jones Thorne.

Expanding the Reach

The EDM job shop initially served the tool & die and aerospace industries, according to ABET Industries Plant Manager Paul Tomac, but over the past half-century has expanded its reach into other industries, including automotive, military/defense, nuclear-power generation, medical and railroad.

“When you have all your eggs in one basket, things are a lot more volatile,” Tomac said. “Today, we try to work in as many different areas as we can. That way, when one industry slows, we can pretty much count on another one picking up.”

Tomac began his EDMing career in 1995 as a service engineer for MC Machinery Systems Inc., Wood Dale, Ill. After 5 years of installing and servicing machines and training shop personnel all over the country, he opted to give up life on the road to spend more time with his family. Learning to make parts on the machines he’d been working with was a logical next step, so after cutting his teeth at various shops in the Chicago area, he joined ABET in 2000 as a team leader.

“When they gave me the opportunity to run the facility,” he said, “I jumped at it.”

One advantage to sinker EDMing is its ability to create tiny, precise features. Both of these parts were received in a machined state; only the highlighted features were EDMed, but any imperfection in the profile would have led to scrapping the finished part. Images courtesy E. Jones Thorne.

EDM as a Specialty

In the old days, EDM was incredibly specialized—it existed to do jobs no other technology could, according to Tomac. The machines were manually operated and incredibly slow, but they could erode even the hardest, toughest metals. As other technologies improved, so did EDMs.