Copyright 2011: EDM Laboratories. Wire EDM. All rights reserved.
EDM (electric discharge machining) is a process which removes metal by vaporizing it with a spark. Anyone who has ever dropped a wrench across a car battery has witnessed a very crude form of EDM. The modern EDM process uses high frequencies, sometimes creating hundreds of thousands of tiny sparks per second. A servo motor changes the feed rate of the electrode to keep the voltage constant and a dielectric fluid serves the purposes of acting as a dielectric barrier to allow the charge to build up, a coolant to prevent the electrode from getting hot, and removing the vaporized metal particles. Early models in the 50's like the ELOX M200 were mainly used to remove broken taps and drills. As they became more sophisticated and larger, they were used to burn dies, and were commonly called die sinkers - many people refer today to vertical EDM's as sinkers because of this. Also called "ram" and "conventional" EDM, this type of EDM employs an electrode cut to the shape of the desired cavity. The advantage of the conventional EDM is that it can do 3 dimensional cuts. The disadvantage compared to wire EDM is that it requires an electrode and is relatively slow. When preparing jobs for conventional EDM, it is best to remove as much material as practical conventionally as the EDM process is slow. In wire EDM, the opposite is true. Conventional EDM's generally use specialized oil as a dielectric, although there are a few that use water.
We have 4 CNC EDM's including a Sodick AG60 with linear motors purchased in September of 2012, and a Sodick AD35L purchased in 2015.
Wire EDM uses a spool of wire as an electrode and is programmed to cut the desired shape.
Four axis wire's can cut tapers and different shapes on the top and bottom of the part. The wire can be as small as .0005", however we do not use smaller than .004, simply because life is too short to deal with .0005" wire. Wire EDM uses water as a dielectric and good flush pressure is critical. It is important to leave stock around the area to be cut whenever possible, and flat surfaces on top and bottom work best. It is not advisable to rough machine before wire cutting - it usually slows it down. Also consider that the part is suspended off the edge of the table so the heads holding the wire can travel around the part unobstructed. Try to leave an inch or two of material beyond the cutting area for clamping. When in doubt, send us a drawing. Our wire EDMs have cutting envelopes up to 24 x 16" and up to 20 " thick.
Small Hole EDM uses a brass or copper tube as small as .004 dimeter up to 1/8" diameter with high pressure water to EDM holes very quickly through even the hardest metals. It is commonly used for start holes for the wire EDM and removing broken drills and taps, but also can be competitive against conventional drilling in many instances. A small hole EDM can put a .020" diameter hole through 1" of tool steel in less than 2 minutes, even after heat treat. It also can shine on angled surfaces such as wire holes in hex nuts.
The main factors for machinability when cutting with a spark are density, melting temperature, and electrical conductivity. This makes aluminum cut quite quickly compared to tungsten. Some materials such as copper and titanium cut well on the wire but are difficult on the sinker as they wear the electrode out quickly.