Electric discharge machine

Electric discharge machine

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Electric discharge machine is a non-conventional method of machining complex shapes which are very difficult to be formed with equal accuracy with any other method. This method doesn’t need any hardened expensive tool or enormous pressure to cast a shape in steel, rather it incorporates high current electricity and a cathode of the same shape and size of the pattern to be formed to cast the required shape in the metal. Against other methods where tool used is of higher hardness and strength than the material to be cast, this machine uses cathodes of lower hardness and strength then that of the material to be machined. Generally, cathodes used are made up of either graphite or cooper or aluminum. The most important qualities required to select the material of electrode is that it must be highly conductive, must possess higher electronegativity than the material to be cast and must be soft so that it can be easily machined into different shapes.
An electric discharge machine is also known as EDM (which is its short form name) for the ease of conversation. It is also known as die sinking machine because the die which is the cathode sinks in the material and forms the required shape.

Functioning-
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In this machine, the material in which the shape is to be formed is fixed in a lined vessel. Then the vessel is filled with any suitable die-electric fluid. Transformer oil and kerosene oil are most common and easily available fluids. The amount of die-electric is such that the metal to be cast is fully immersed in it. The material is removed by spark erosion. For this purpose an electrode is machined in the accurate shape and slightly smaller size than the required with a CNC machine. This electrode is mounted at the top of the immersed job. The job is connected to the positive terminal of a D.C. supply and the electrode mounted above is connected to the negative terminal of the supply. When the machine is switched on the cathode starts coming down towards the anode. When both anode and cathode are at the suitable distance from each other, an spark is produced between the electrodes which erodes the metal from the anode. The cathode mounting is attached to a servo mechanism which reverts back the cathode whenever it comes in contact with the anode and maintains the gap between electrodes. This is necessary for smooth cutting of the material.

Electric discharge machine is used when we have to make internal complicated shapes which can’t be made with CNC or pantograph. Die sinking is one of the most accurate processes of machining steel though it is slow and expensive. Generally, dies for injection molding machine are made with EDM, as it has complicated internal shapes which need to be highly accurate and can’t be made with forging or CNC and so much expanse is affordable if extremely high accuracy is needed.

Essential parts of an EDM-
1.         Transformer to induce low voltage to high voltage.
2.       Inverter to convert A.C. to D.C.
3.       Servo mechanism
4.       Suitable Dielectric
5.       Cathode


       Credits: Image Source- Google Images


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