Unlike conventional metal cutting processes, non-traditional machining (NTM) processes can directly employ different forms of energy for controlled removal of material from the workpiece to impart desired shape, size and finish. Electro-Discharge Machining (EDM) is one thermal energy based process where material is removed by localized melting and vaporization. Intense heat is generated by means of electric sparks. Here the tool made of conductive material is made one electrode (cathode), while the conductive workpiece is made another electrode (anode); and a small gap is maintained between the two. This gap is again filled with dielectric fluid. When sufficient potential is applied across the two electrodes, the dielectric brakes down to assist spark formation. Spark temperature can reach as high as 10,000°C. Such high temperature spark instantly melts and vaporizes material and creates a small cavity (of nanometric dimension) on the work surface. Repeated generation of such sparks in a controlled way can lead to the production of highly finished surface.
As the name suggests, Electro-Chemical Machining (ECM) is one electro-chemical energy based NTM process where material is removed by ionic dissolution following the principles of Faraday’s Law. Here thermal energy has no direct role in material removal. No such spark is also generated here. However, similar to EDM, the tool electrode and workpiece electrode is connected with two terminals of the electrical power source and a small gap is maintained in between them. This gap is filled with suitable electrolyte. When sufficient potential difference is applied across two electrodes, electro-chemical reaction initiates. As ions liberate the worksurface to participate in reaction, material removal occurs in a very minute scale the form of ions (ionic dissolution). Materials for tool electrode as well as electrolyte must be selected in compatible with the work material so that only material removal from work surface takes place and the tool remains intact. Various similarities and differences between ECM and EDM are given below.
Similarities between EDM and ECM
- EDM and ECM both are so called non-traditional machining processes. However, they are not hybrid processes.
- Both the processes take assistance of electrical energy for material removal; however, their material removal mechanisms are different.
- They can be applied for electrically conductive materials only. For non-conductive materials, coating strategy can be adopted in some cases, but the process capability and accuracy will not be satisfactory.
- Both the processes require an additional source of power (typically DC power generator) to maintain sufficient potential difference between two electrodes.
- A form electrode having profile according to the intended final shape on workpiece is indispensably required in both the cases.
- Mechanical properties of work material (such as strength, hardness, brittleness, etc.) pose no restriction on the applicability to these processes.
- Both the processes are usually free from burr, residual stress, and other thermal damages to the work surface. Although EDM is based on thermal energy, but heat is generated locally and thus has negligible thermal impact on machined surface.
Differences between EDM and ECM
| Electro-Discharge Machining (EDM) | Electro-Chemical Machining (ECM) |
|---|---|
| EDM is thermal energy based non-traditional machining process. | ECM is electrical energy based non-traditional machining process. |
| Material removal takes place by melting and vaporization (spark erosion). It is one volume removal process. | Material is removed by controlled electro-chemical dissolution of work metal (anode). Material removal takes place in the form of ions (instead of direct volume removal). |
| Owing to electric spark, significant heat is generated in EDM process. The localized temperature reaches as high as 10,000°C. | No heat generation takes place in ECM. |
| An appropriate dielectric fluid (such as kerosene, paraffin, deionized water) is used in EDM to assist spark generation. | A suitable electrolyte (such as NaCl and NaNO3) is applied in ECM to assist flow of ions between two electrodes. |
| During EDM operation, electrode material is also removed gradually along with workpiece material. However, electrode material removal rate is much lower than work material removal rate. | Electrode does not suffer any wear during ECM process. Same electrode can be used repeatedly for a longer duration. Accordingly, electrode life is higher. |
| EDM process typically requires high potential difference (50 – 400V) and moderate current (100 – 200A). | ECM process requires moderate voltage (<50V) but very high current (>1000A). |
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).