By Mark Shortt

Wire EDM uses a thin piece of wire - typically made of brass, copper, or tungsten - as the electrode. A variation of conventional ram or sinker EDM, the process is said to be similar to contour cutting with a band saw. Because it uses the heat of an electrical conductor to vaporize material without the aid of cutting forces, it is well suited to machining parts that have complex geometries. Today's 5-axis machines are capable of producing geometries "which cannot be produced with any other machining techniques," according to Bob Tarantino, president, New Jersey Precision Technologies, Mountainside, New Jersey.

 

The process is also used to cut thick metal plates and produce a variety of tools, punches, and dies from hard metals. Gears, rotors, turbine blades, and intricate electronics components are all produced by means of wire EDM, also known as electrical-discharge wire cutting.

 

A vertically oriented wire, constantly renewed as it travels from a supply spool to a take-up spool, is fed into the workpiece. A power supply provides voltage between the wire and the workpiece; deionized water is used as a flush/coolant.

 

Maximum cutting speeds of wire EDM increased dramatically during the 1980s, going from approximately 3 square inches per hour to between 18 and 20 square inches per hour, according to Larry McNellis, president, AcuCut Inc., Southington, Connecticut. Since then, speeds have increased to about 25 square inches per hour, depending on the workpiece material and thickness, Mr. McNellis said.

 

Wires have typical diameters of 0.010-0.012 inch. As wire diameters have decreased through the years, narrower cuts have become possible, but at significantly higher costs. Today, wires can be as thin as 0.001-0.003 inch in diameter.

 

"Years ago, we cut something using 8/10-inch-diameter wire," said Mr. McNellis. "Now, the normal size is 10-to-12 thousandths diameter. We've also cut parts over 36 inches thick," he said.

 

One of the keys to maintaining this versatility is the ability to change tooling to suit the different requirements of each job. Most of today's CNC machines are equipped with automatic tool changers, which enable companies to do just that.

 

Today's multi-axis, CNC wire EDM machines have incorporated a number of process enhancements that have delivered greater automation. In addition to automatic tool changers, capabilities include automatic self-threading of the wire in case of breakage, multiheads that permit cutting of more than one part at a time, and programmed machining strategies.

 

Some companies, such as AcuCut, also use a central filtering system to filter water through all of their wire EDM machines. The technology is economical because it eliminates the need for filters at each machine.