THE JOB SHOP

ELECTRICAL DISCHARGE MACHINING

Wire EDM is a method to cut any conductive materials such as steel and aluminum with a thin brass or Molybdenum traveling wire electrode that follows a CNC (Computer Numerical Code) programmed path. Wire diameters from .001 - .013 The most typical being .010 leaving a .005 corners radius that is acceptable in most applications. The Wire EDM machines are rated to cut their best through heat-treated Steel - 2 inches thick. The hardness of the work piece material does affect overall speed. Flatness for high pressure flushing is also an issue, the flatter the work piece the faster the process. The traveling wire never touches the part being machined, consequently Wire EDM machines do not take the abuse like a CNC Mill does, therefore staying more accurate through the years compared to Mills & Lathes. 

The process is fascinating, the wire is charged with electricity of special type, not like what comes out of your 110 V receptacle at your house. As a spark jumps from the traveling wire electrode in precise measures, it’s simultaneously melting a small portion of the conductive work piece. Deionized water is used to flush the particles from the gap. 

In reality, the electricity excites the molecules in the deionized water which does the EDM cutting (Electrical Discharge Machining). The traveling wire electrode is just a tool for transferring the power to the water. It is important to note that the water is of a special conductivity- considered deionized, it is kept at a very specific low number that isn’t inclined to transfer electricity as well as tap water. This is the reason why you don't get electrocuted to death if your body is in contact with the water.

CNC Wire EDM machines can independently move six machines axes to generate taper cuts, turn & burn type parts like a rotor and stamping dies with angle relief for slugs. Tapper capability depends on machine manufacture, Mitsubishi EDM is about 15 degrees whilst Charmilles EDM can cut 45 degrees or more. Wire EDM can be accurate to +/-.0001 depending on how many passes one is willing to wait for, since the process is slow. Most shops find one rough cut / one pass of the wire is more accurate than they ever worked in their lives usually a couple tenths. No burrs are generated.

Wire EDM is ideal for manufacturing delicate parts since there are no cutting forces. In general, heavy investments in Stainless Steel Tooling are required to hold parts flat & square whilst the EDM process is happening. The Tooling has to be to par, while the wire never touches the work piece, the machines present high-water pressures of 300 psi or more directly to the part being machines. So vibration and movement of the work piece can present difficulties in part setup. The concept of wire EDM is to cut the parts after heat treat, so that there is no heat producing warpage to contend with, especially in intricate parts.  

Some machines can cut parts that are 30 inches tall, however it is a very slow process and only used in extreme applications where the shape can be made no other way.