“There’s more than one way to skin a cat,” as the old expression goes. Similarly, there’s typically more than one way to cut parts. Compared with conventional machining—from basic CNC turning all the way up to 5-axis—EDM has certain advantages and disadvantages. So, if you’re wondering whether EDM is the best bet for your particular application, the answer is always the same: it depends on your application.
Generally speaking, however, the principle characteristics of electrical discharge machining should give you a sense of whether EDM is a good fit for your application. For example, EDM is typically slower than other machining methods, but it also tends to be more predictable, accurate and repeatable. There are other benefits as well, as Pfluger pointed out: “All EDM machining is performed unattended,” he said, “so the direct labor rate and the cost of manufacture with EDM are typically lower than other methods.”
The combination of predictability, accuracy and repeatability—combined with its relatively slow machining speed—explains why EDM is most at home in low-volume operations with tight tolerances, such as the aerospace and medical device industries.
“The biggest point in favor of piece part manufacturing with wire EDM is when you get into part detail and you’re trying to do it with a slitting saw or a grinder, or any type of friction machining, which is going to create a burr,” said Langenhorst. “In that case, you have to have a secondary process for burr removal, whether it’s vibratory or having a bunch of workers scratching the burrs off with hand tools. On the other hand, when you take a part off an EDM machine, there is no burr: it’s perfect.”
Pfluger pointed out another advantage to using electrical discharge machining for parts with small or complex features: “The EDM process becomes more attractive as workpiece materials become harder, and as the part geometry becomes smaller and deeper,” he said. “Unlike conventional milling, EDM does not encounter limitations with L:D as internal radii features become smaller and workpiece thickness increases. In general, the EDM process is reserved for smaller part feature sizes and higher accuracy requirement applications (+/- 0.0005” or +/- 0.012mm or finer accuracy).”
Moreover, since EDM is a non-contact machining process, the fixturing requirements for cutting small parts are considerably less onerous compared to those of a standard CNC mill. “There’s no cutting pressure, so if you’re working with little tiny pieces, you don’t need much of a fixture to hold them,” said Langenhorst. “If you tried to mill them, have you to have it held tight enough that your machining process won’t pick it up or bend it. For example, if you’re doing core pins for molds and you try to grind them, they’ll move all over the place. You can wire cut those with just a 90-degree flip fixture and they come out great.”