Short notes for GATE Mechanical Engineering - Electro Chemical Machining
In this article, we continue our series of articles on Unconventional Machining Short Notes for GATE Mechanical Engineering. Let us have a look at Electro Chemical Machining.
Electro Chemical Machining is a process which is an extension of an already known process of electroplating with some modifications, in a reverse direction. A shaped tool or electrode is used in the process, which forms cathode. The workpiece forms anode. A small gap is maintained between the tool and workpiece and an electrolyte is pumped through it.
The electrolyte used possesses such properties such that the constituents of the separated workpiece material do not stick on the tool surface. Most widely used electrolyte in the process is Sodium Nitrate solution. Sodium chloride solution in water is also an alternative but it is more corrosive than the former.
All metals can be machined by this method. However, its application is only suitable for mass production work as the tooling and initial cost is high. This process can be used to machine extremely hard metals and alloys, deep holes, small size and odd shaped holes.
The tools used in this process should be made of such material which have enough thermal and electrical conductivity, high chemical resistance to an electrolyte. The principle of ECM is based on Faraday's Laws of Electrolysis. The workpiece acts as anode while the tool acts as cathode. The tool and workpiece are held close to each other with a very small gap (say 0.5 mm) between them. A mild DC voltage of about 3 to 30 V is applied between the two and an electrolyte is continuously pumped into the gap. Due to the applied voltage the current flows through the electrolyte with positively charged ions being attracted towards the tool (cathode) and the negatively charged ones towards the workpiece (anode) the electrochemical reaction, taking place due to this flow of ions, results in the removal of metal from the workpiece in the form of sludge. This sludge is taken away from the gap by the flowing electrolyte along with it.
Advantages of ECM:
- Any good electrically conducting material can be machined and its mechanical properties have no bearing on its machinability through this process.
- Intricate and complex shapes can be machined easily through this process.
- Metal removal rate is quite high in comparison to traditional machining, specially in respect of high tensile and high temperature resistance materials.
- Wear on tool is insignificant or (say) almost non-existent.
- The machined work surface is free of stresses.
- No cutting forces are involved in the process.
- High surface finishes, of the order of 0.1 to 2.0 microns, can be obtained.
- It is an accurate process and close tolerances of the order of 0.05 mm can be easily obtained.
- With the application of such process, many machining operations like grinding, milling, polishing etc. can be avoided.
Disadvantages of ECM:
- Materials which are non-conductors of electricity cannot be machined.
- Power consumption is very high.
- Corrosion and rusting of workpiece, machine tool, fixtures etc. by electrolyte is a constant menace.
- Required initial cost is very high.
- Extermely fine corner radii, say less than 2.0 mm cannot be produced.
- Designing and fabrication of tools is difficult.
Application of ECM:
- Machining of hard to machine and heat resistant materials.
- machining of blind holes and pockets, such as in forging dies.
- Machining of complicated profiles, such as of jet engine blades, turbine blades.
- Drilling small deep holes, such as in nozzles.
- Machining of cavities and holes of irregular shapes.
- Deburring of parts.