Wire EDM vs. Ram (or Sinker EDM)
Wire EDM machine
Wire EDM machines have advanced since the 1970’s when it was first introduced in speed, workpiece size, taper, price, accuracy and with EDM machines, unattended operation abilities. It uses a single string of thin metal wire for precise incisions in thick metals. The parts are submerged in deionized water and the wire acts as the electrode. Water flushes away the debris for a very clean saw-like cut.
Cutting speed has increased as technology has advanced over the years because of higher flushing pressure and faster solid-state generator circuitry, among other things.
When selecting a wire EDM machine, you’ll notice that newer machines come in a wide range of sizes. Dimension on all axes have increased, but now you can get machines with much more z-axis. The machine travels should be listed for any used EDM machine. Early models of EDM were for die making, and a 1-degree die relief to 4 or 5 inches used to be the maximum possible taper. New machines by Mitsubishi, like the MV1200-S for example, have 45 degrees @ 1.8” wide angle taper options.
Wire EDM machine manufacturers
Wire EDM machines are made by a wide range of manufacturers like Sodick, Sharp, Makino, Charmilles, Agie, Mitsubishi, Kent, Brother, Perseo-Eri, Belmont, Aneutronic, Sunwind and more. This has kept pricing relative competitive over the years.
Electrical discharge machining is particularly known for amazing accuracy. The technology allows for equipment even from the early 2000s, to go down to .00005”. The resolution for the MV1200-S of 2018 is 0.000002”. This is possible with wire diameters as small as .004”. CNC operated EDM’s with automatic workpiece loading can run unattended and significantly improve shop productivity.
Ram (Die-Sinking) EDM
Manual die sinking EDM began around 1955 and gradually improved until the first CNC EDM units were introduced in the 1980s. It is the conventional form of EDM and is usually used to produce blind cavities. Ram EDM uses spark erosion to remove metal along the surface of a formed electrode. One disadvantage of RAM electrical discharge machining is the mess it can make in your shop. Graphite electrodes can make your shop full of graphite dust, so it’s advised to use filtration systems.
The speed of making parts with RAM EDMing has improved greatly over the years. On very old machines, high electrode wear often made it necessary to rough out cavities before doing RAM EDMing. But with solid-state power supplies and premium electrodes, it’s possible to use no-wear settings to rough and then finish in one setup.
Orbiting in ram EDM allows for a roughing electrode to often be used also for finishing. Previously, it was common to need multiple electrodes to rough a cavity and then more to finish it. Orbital paths aid in flushing the cavity by creating a pumping action. The electrode can cut not only the bottom but also along the sides resulting in a much greater surface area being machined at once.
Orbital paths possible in ram EDM include down machining, vectorial machining, directional machining, conical machining, horizontal planetary machining, cylindrical machining, helical machining, concave spherical machining, and convex spherical machining.