Electric Discharge Machining (or EDM) is a non-traditional machining process where rapid pulsed high electric discharge is applied between an electrode and the work piece that generates huge amount of heat that melts and vapourises surface atoms of the metal from the work piece. In other words, the spark that is generated between the work piece and the electrode is powerful to erode the work piece that is in the closest proximity to the electrode. Both the electrode and the work piece are submerged in a dielectric medium such as de-ionised water which serves both as a controlled medium for flow of electrons between them in the spark gap and also to wash away the micro chips that separate from the work piece during machining. The EDM is non-traditional in the sense that no cutting tools are used to remove material from the work piece mechanically such as in a conventional machining process. There are broadly three types of EDM. Let’s see what they are.
Types of EDM
1. Ram or Sink EDM or Die Sink EDM
In this method the electrode is made from soft material that is in the exact shape and form intended to remove a cavity from the blank out of that shape. During each electric discharge pulse, the electrode lifts and sinks by a small distance into the work piece thus removing the material in each cycle. This is used to produce tool dies with geometries that are not possible to machine conventionally. However, the shape of the electrode has to be pre-machined to the required shape and size.
2. Wire EDM
In Wire EDM, the electrode is in the form of thin wire of diameter 0.1 to 0.3 mm. The wire is fed from the side to cut away the work piece. If the cut as to be made internally, a hole is drilled and wire is fed through it and then feed is given to the wire to make the cut.
3. Drill EDM
As the name suggests, the electrode is in cylindrical form that travels into the work piece to drill tiny holes.
Electrode is made of copper, brass, graphite or tungsten carbide. Graphite is easier to form into the shape than copper, but conductivity is less. Copper has good conductivity but has less resistance to erosion.
Work Piece Materials
Any conductive metals like steel, copper, titanium, aluminum, alloys and super alloys can be cut.
Sink and Drill EDM is used for cutting the cavities for injection mould tools and dies for pressure die casting. Wire EDM is used for cutting blanks and punches of required shape out of thick plates and also to cut the dies for extrusion. It is also used to cut and remove metal 3D printed parts out of the base build plate.