EDM stands for Electrical Discharge Machining. The basic concept of EDM is that you use an electrode to erode a workpiece using electrical sparks. The electricity flows through the electrode in the form of a square wave attacking the points of least resistance on the workpiece similar to how a bolt of lightning would hit a tree before it hits the ground. This "Zap" happens every time the current is switched on in the square wave and then the current is switched off to allow the debree to be flushed away. This process happens over and over many times a second as the electrode is slowly advanced deeper and deeper into the cut. The electrode never touches the workpiece because the actual cutting is being done by the spark gap between the electrode and the workpiece.

The process takes place submerged in a dielectric fluid such as deionized water or dielectric oil. This fluid acts like the vacuum in a light bulb. If you break a light bulb, the fillament which has current flowing through it becomes oxidized and burns out. The same would happen if you tried to EDM without any dielectric, the electrode and workpiece would become oxidized and would not be able to perform the cut. The Dielectric fluid performs multiple tasks; 1) Providing an inert atmosphere in which the process can take place. 2) Flushes the removed material or debree away from the gap. 3) Keeps the gap cool and the temperature of the whole process stable.

There are three main types of EDM which are different according to the type of electrode used.

• Wire EDM in which the electrode is a brass wire that comes off a spool and is fed through an upper and lower diamond guide and then discarded after it is used. The wire is controlled by a CNC control which allows you to program a path for the wire to travel along sort of like a super precision band saw. The wire can range from .0120 to .0008 inches in diameter. This form of EDM is the most accurate and is able to hold size well under .0001 inches.

  

• Sinker EDM in which the electrode is a machined shape made of materials like graphite, copper, or copper-tungsten (to name a few) and the machine uses this shape to erode the inverse shape in the workpiece. This process is also very accurate and commonly used to burn mold cavities where the electrode starts out the shape of the final molded part and is used to erode a cavity in a mold that is later used to make thousands or millions of parts.

  

• Small hole EDM drill ("Hole Popper") in which the electrode is a brass or copper tube ranging from .004 to .250 inches in diameter that is used to blast holes through the workpiece. This process is similar to Sinker EDM except that sinkers have very sensitive power supplies to protect and conserve the electrode and the popper has a very aggressive power supply to blast through the workpiece very quickly. This type of EDM compliments the wire EDM by providing the ability to drill pilot holes through heat treated materials and carbide so that you can thread the wire through this pilot hole for a place to start your wire cut.

Polcraft inc. employs all three types of EDM in addition to CNC and conventional milling and turning to eliminate any out sourcing of the manufacturing process so you get high quality parts in a timely fashion. Have more Questions? Email me Mark Filipowicz directly and I will be happy to answer them for you.