Electrical Discharge Machine (EDM)

OBJECTIVE

The objective of this experiment/demonstration is to illustrate the Non-Traditional Machining (NTM) process using EDM, the machine features, process capabilities, and limitations. Students should also understand the importance of the NTM technique used in this era.

 

APPARATUS

Electrical Discharge Machining (EDM), Specimen (mild Steel), Dielectric (paraffin).

 

Figure 1.0 The EDM electrode together with flushing system and magnetic table top.

 

THEORY

 

1. EDM machine working principle is electrical discharge or sparks erosion which melt the surface of the work piece, evaporates and aided by cavitations.
2. The sparks travels from the electrode to the work piece through a gap and dielectric.
3. The tool (electrode) can be softer or more ductile than the work piece.
4. Only electric conductive materials can be machined using EDM.

 

 

PROCEDURE

 

1. Firstly, work pieces are placed on the table top and they are hold using magnetic force.
2. Then, the electrode is lowered down to take the dimension of the work piece; from top to bottom and from left to right.
3. The flushing technique is selected either suction or spray flushing to remove the burrs while the process take place.
4. Next, the confinement of the work piece and electrode is closed and dielectric is filled in until the electrode and the work piece are fully immersed.
5. After that, the process is selected from the machine from various tasks for example hunting or speed up process.
6. When everything is set up, the machine is switched on.
7. The machine is stopped when the process is done. Then, the dielectric is drained out from the confinement.
8. The magnetic table top is release and the work piece is removed to be analyzed.

 

RESULT

 

There are two types of method being selected while executing the process towards the work piece and they are speed up and hunting.

1. Speed up - In speed up method, the sparks that being produced by the electrode is delivered much faster and in higher rate. Thus, it results faster machining time but however produced poor surface finish. The surface finish for this process selection is rougher and may suitable for products that do not desire good surface finish.
2. Hunting - For hunting method, the sparks are delivered in a lower rate compared to the speed up method. Thus, this process is time consuming. In the other hand, the surface finish produced from this process is much better compared to the speed up process and is preferable for products that require accuracy and good surface finish.

     

Figure 1.1 Samples of the electrodes            Figure 1.2 Sample of the specimen, speed 

                                                                                    up (left), hunting (right).                         

                 

DISCUSSION

           

            There are six basic steps in an EDM process. These basic steps are listed as below;

i.                     The electrode approaches the work piece. Then, the two units are energized.

ii.                   The concentration of the electrical field towards the point where the space between the electrode and work piece is the smallest.

iii.                  Creation of an ionized channel between the electrode and work piece.

iv.                 Breakdown of the spark. The work piece material melts locally and disintegrates. The electrode only wears out slightly.

v.                   The current is cut off causing implosion of the spark.

vi.                 Evacuation of the metallic particles by flushing with dielectric.

 

Using EDM offers several advantages. Commonly the electrode used in EDM is

made from ductile material such as copper but being added with other elements to make it harder to increase the resistance to wear, such as tungsten copper. However, EDM can only machine electrical conductive work piece. As for the capabilities of EDM, it is able to make products with blind complex cavities, micro holes for nozzles, cutting of non-circular holes and cutting of narrow slots.

            However, EDM also have several disadvantages where the power consumption is absolutely high, which is 5 times more than conventional machining. Other than that, critical parameters has to be considered such as voltage, capacitance, spark gap, dielectric circulation, and melting temperature. If any of these aspects are not taken into consideration, errors or failure in work piece may occur. EDM process is also a relatively slow and time consuming machining process. 

 

Figure 1.3 Samples of products from EDM process in keyway making.

 

CONCLUSION

 

            Overall, EDM is one of the Non-Traditional Machining that is becoming popular nowadays. Despite of its limitations, the accuracy and the ability to machine brittle electrical conductive materials is often being taken into consideration. The ability to machine work piece with high accuracy in dimension is one of its major advantages even the machining time is longer than expected. The needs of desired accuracy of dimension can be obtain using EDM. Products of EDM are normally related to dies and moulds where complex shapes are able to be determined. Other that than, EDM is also used to make keyways in items such as gear, which cannot be obtain through the initial process. Keyway making is considered as secondary process and can be done using EDM.