Electrical discharge machining (EDM)

Electrical discharge machining (EDM)

Electrical Discharge Machining (or EDM) is a machining method primarily used for hard metals or those that would be impossible to machine with traditional techniques. One critical limitation, however, is that EDM only works with materials that are electrically conductive. EDM can cut small or odd-shaped angles, intricate contours or cavities in pre-hardened steel without the need for heat treatment to soften and re-harden them as well as exotic metals such as titanium, hastelloy, kovar, and inconel.

Sometimes referred to as spark machining or spark eroding, EDM is a non-traditional method of removing material by a series of rapidly recurring electric arcing discharges between an electrode (the cutting tool) and the workpiece, in the presence of an energetic electric field. The EDM cutting tool is guided along the desired path very close to the work but it does not touch the piece. Consecutive sparks produce a series of micro-craters on the work piece and remove material along the cutting path by melting and vaporization. The particles are washed away by the continuously flushing dielectric fluid. It is also important to note that a similar micro-crater is formed on the surface of the electrode, the debris from which must also be flushed away. These micro-craters result in the gradual erosion of the electrode, many times necessitating several different electrodes of varying tolerances to be used, or, in the case of wire EDM machining, constant replacement of the wire by feeding from a spool.

According to the Manufacturing Reference Guide by Robet H. Todd, Dell K. Allen, and Leo Alting, EDM grinding is a mass-reducing process that uses a rotating conductive wheel to remove electrically conductive material by means of controlled, repetitive spark discharges. A dielectric fluid is used to flush away the chips, regulate the discharge, and cool the wheel and the workpiece.
There are two main types of EDM machines: Sinker EDM (also called Conventional EDM and Ram EDM) and Wire EDM.
Advantages
Some of the advantages of EDM include machining of:
* complex shapes that would otherwise be difficult to produce with conventional cutting tools
* extremely hard material to very close tolerances
* very small work pieces where conventional cutting tools may damage the part from excess cutting tool pressure.

Disadvantages
Some of the disadvantages of EDM include:
* The inability to machine non-conductive materials.
* The slow rate of material removal.
* The additional time and cost used for creating electrodes for ram / Sinker EDM.
* Reproducing sharp corners on the workpiece is difficult due to electrode wear.
EDM is a chip less metal removal process that uses the principle of metal erosion by an interrupted electric spark discharge b/w the tool (cathode) and the work piece (anode) this process is also called liSP ARK EROSION II DIEELECTRIC FLUID

The common dielectric fluids used are paraffin oils transformer oil dematerialized water and kerosene. Dielectric fluids prevent particles of work piece adhering to the tool electrode and increases metal removal rate as compare with operating air. These fluids are hydrocarbons and hydrogen in these fluids provides de-ionizing action necessary for thee fluid to become an effective insulator after each discharge. It remains non conductive till break down occurs, breaks down rapidly when critical voltage is reached and then de-ionizes rapidly after the condenser as discharge. Low viscosity fluids make the flow easy.

A general guide to the selection of appropriate tool material for different

material is given below:

Electrode	Work piece
Copper	Aluminum
Copper	Brass
Copper	Steel
Copper Tungsten	Copper
Copper Tungsten	Steel
Copper Tungsten	Tungsten carbide
Graphite	Aluminum
Graphite	Steel
Graphite	Zinc alloy
Steel	Steel