Non-Traditional Machining (NTM) processes had evolved to eliminate the restrictions imposed by conventional metal cutting processes. For the sake of material removal, NTM processes directly utilize various forms of energy (like mechanical, electrical, thermal, chemical, electro-chemical, ionic, light, etc.). One such thermal energy based NTM process is Electric Discharge Machining (EDM). EDM utilizes an electrically conductive tool electrode that has a specific shape. This electrode is then brought closer to the conductive workpiece and a small gap (0.2 – 1.0mm) is continuously maintained in between them. This gap is, however, filled with suitable dielectric fluid. The conductive tool and the conductive workpiece act like two electrodes on an electric circuit. When sufficient potential difference is applied between these two, the dielectric breaks down to form a spark. The spark strikes the work surface and increases the localized temperature to as high as 10,000°C. This results localized melting and vaporization of work material, and hence material removal.
EDM process can be carried out in several ways following the same abovementioned principle. Accordingly different variants of EDM have evolved, two of them are die sinking EDM and wire EDM. Die sinking EDM (also called conventional EDM) employed a tool electrode having a profile matching with the intended shape. The electrode usually has a larger face. It is used to impart multifarious blind shapes and surface curvatures. On the other hand, Wire-EDM (W-EDM) (also known as Wire Cut EDM, WC-EDM), employs a conductive wire as tool electrode. This wire is continuously moved between two fixed pulleys and the workpiece is fed against the wire. So the spark is generated between the wire and workpiece. It is suitable for through profile cutting or sample preparation. It cannot make any blind feature as the wire is required to pass through it. Various similarities and differences between die sinking EDM and wire EDM are given below in table format.
Similarities between Die Sinking EDM and Wire-EDM
- Both die sinking EDM and Wire-EDM are thermal energy based non-traditional machining processes. None of them is considered as hybrid process.
- The mechanism of material removal is same in both the cases. This mechanism is nothing but spark erosion or melting and vaporization of work metal due to extreme localized temperature of spark.
- Suitable dielectric fluid (like deionized water, kerosene) is applied in both the cases to assist spark generation and debris removal.
- Presence of suitable potential difference between tool electrode (cathode) and workpiece (anode) is indispensably necessary for breakdown of dielectric fluid.
- None of them is associated with the production of burr, residual stress, etc.
- None of them relies on mechanical properties of work material such as strength, hardness, ductility, etc. However, electrical conductivity is one mandatory property of work material.
Difference between Die Sinking EDM and Wire-EDM
| Die Sinking EDM | Wire-EDM |
|---|---|
| A die made of conductive metal is used as tool electrode (cathode) to liberate electrons for producing spark. | Instead of die, a long small diameter wire made of conductive metal is used as tool electrode or cathode. |
| The die can be given complex 3-D profile. Accordingly, die sinking EDM can produce intricate shapes and features on the job. | The wire always has a same simple geometry. So Wire-EDM is not suitable for producing 3-D contours. It is preferred for 2-D cutting only. |
| It can produce blind features (like holes or cavities that are not open in bottom end). | It cannot produce any blind feature. It is applicable for profile cutting by means of through holes only. |
| It can start machining at any location on the workpiece irrespective of presence or absence of edge or through hole. | It can start machining from edges only. To initiate W-EDM at an intermediate location on workpiece, a through hole (starter) is required to fabricate using other operation for the passage of wire. |
| Die sinking EDM is commonly used for 3-D contouring, finishing, drilling, deburring, etc. | W-EDM is mostly used for high accuracy profile cutting, sample preparation and separating or parting off. |
References
- Unconventional Machining Processes by T. Jagadeesha (I. K. International Publishing House Pvt. Ltd.).
- Advanced Machining Processes by V. K. Jain (Allied Publishers Private Limited).
- Nonconventional Machining by P. K. Mishra (Narosa Publishing House).