Traditional machining works through mechanics. Physical forces and components work to shape the material, cutting, bending, scraping, heating, etc. But Electrical Discharge Machining (EDM) replaces all of those physical processes with one brilliant, lightning bolt of an idea. No literally: you machine with lightning.
EDM doesn’t cut with material; it cuts with electricity. And the current, surprisingly, doesn’t need to be very strong. Opposite currents are run along the “blade” and the material to be cut. As the “blade” and the material close the distance, thousands of tiny sparks explode between them. Each spark obliterates a small amount of even the toughest metals.
Simultaneously, machinists run a constant stream of dielectric fluid along the cut, conducting electricity, cooling, and cleaning vaporized material.
When Would You Use Electrical Discharge Machining?
The two most common reasons for EDM are hard materials and precision.
Because EDM uses electricity rather than physical material blades, you don’t need to find a blade that is stronger than the material you are cutting. Carbide? Not a problem with EDM. Electricity cuts straight through carbide like a hot knife through salted butter. EDM can cut ANYTHING.
EDM is also mandatory when you need extreme precision. The blast radius of the tiny sparks is also known as the overburn. Overburn is approximately 2-5 microns, depending on the type of blade you are using. That is up to five-millionths of a meter, or five-thousandths of a millimeter, many times thinner than even the thinnest of human hair.
But at the rate of 20,000–1,000,000 sparks per second, you can really cut through material fairly quickly and cheaply. That level of precision is impossible to reach in more traditional machining, where 20 microns is the upper bound.
Being able to cut materials with less than 5 microns of wiggle room allows engineers to craft interlocking materials that are so close together, they are almost airtight. That’s why this spade shape slides so slowly down into its holder.
When Wouldn’t You Use Electrical Discharge Machining?
Not to knock on traditional machining, but EDM is so cool, why would you ever use metal when you could use lightning?
It turns out, there are a few big constraints that make traditional machining the better choice for many applications.
The biggest problem with EDM is speed. Although hundreds of thousands sparks per second does add up quickly, the process is much slower than physical cutting. This assures that in cases where 20 microns is enough precision for you, and the material is not super strong, traditional machining remains king.
Types of EDM for different job types
Another problem that comes up has to do with the properties of current, itself. In order to have current, you need to be able to loop the “blade” back on itself.
Wire EDM uses an incredibly thin wire to conduct current, moving this through the material like an electrified jigsaw. The downside of wire EDM is, of course, you need to cut clean through the material.
Die Sinker EDM starts with the creation of, typically, a graphite electrode. The electrode is then used like a stamp, plunging into the workpiece to create complex cavity shapes.
Now, what if you want to cut a complex hole through a thick slab of carbide? You can’t use a die sinker, and you can’t use wire until you can run a wire from one side of the slab to the other.
Machinists have solved this problem with hole-drilling EDM. To create that pilot hole, use a “hole popper.” Hole poppers are rotating, conductive tubes that can be used to burn precise holes, and they can be used in tandem with wires to produce intricate, precise shapes in the hardest materials.
The different forms of EDM ensure that even the hardest materials can be shaped into intricate designs with very few constraints on form, making lightning one of the most useful niche tools machinists have at their disposal.
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– Anthony Machine