Electro Chemical Machining:

The process of metal removal using electro – chemical means formetal removal by forming an electrolytic cell between work piece (as anode) and a tool (as cathode) in the midst of a flowing thin film of electrolyte, is known as electro-chemical machining or electrolytic machining.

Working Principle: The process works on the two well known Faraday’s laws of electrolysis. The metal is mainly removed in the form of sludges and precipitates by electro chemical and chemical reactions occurring in the electrolytic cell.

According to Faraday’s first law of electrolysis, the amount of any substance dissolved or deposited is proportional to the quantity of electricity that is passed through the electrolyte.

According to Faraday’s second law of electrolysis, the amount of any substance dissolved or deposited by the same quantity of electricity is proportional to the chemical equivalent or equivalent weight of the electrolyte.

Electro chemical machining (ECM) process uses electrical energy in combination with chemical energy to remove the material of work piece. This works on the principle of reverse of electroplating. Electro chemical machining removes material of electrically conductor work piece. The work piece is made anode of the setup and material is removed by anodic dissolution. Tool is made cathode and kept in close proximity to the work piece and current is passed through the circuit. Both electrodes are immersed into the electrolytesolution. The cavity machined is the mirror image of the tool.

Work piece: Work piece is made anode,electrolyte is pumped between work piece and the tool. Material of work piece is removed by anodic dissolution. Only electrically conducting materials can be processed by ECM.

Tool: A specially designed and shaped tool is used for ECM, which forms cathode in the ECM setup. The tool is usually made up of copper, brass, stainless steel, and it is a mirror image of the desired machined cavity. Proper allowances are given in the tool size to get the dimensional accuracy of the machined surface.

Power Supply: DC power source should beused to supply the current. Tool is connected with the negative terminal and work piece with the positive terminal of the power source. Power supply supplies low voltage (3 to 4 volts) and high current to the circuit.

Electrolyte: Water is used as base of electrolyte in ECM. Normally water soluble NaCl and NaNO₃ are used as electrolyte. Electrolyte facilitates/acts as carrier of dissolved work piece material. It is recycled by a pump after filtration.

Tool Feed Mechanism: Servo motor is used to feed the tool to the machining zone. It is necessary to maintain a constant gap between the work piece and tool, so tool feed rate is kept accordingly while machining.

In addition to the above, whole process is carried out in a tank filled with electrolyte. The tank is made of transparent plastic which should be non-reactive to the electrolyte. Connecting wires are required to connect electrodes to the power supply.

Applications of ECM Process: There are large number of applications of ECMs. Some other related machining and finishing processes.

(a) Electro chemical Grinding: This can also be named as electro chemical debarring. This is used for anodic dissolution of burrs or roughness a surface to make it smooth. Any conducting material can be machined by this process. The quality of finish largely depends on the quality of finish of the tool.

(b) This is applied in internal finishing of surgical needles and also for their sharpening.

(c) Machining of hard, brittle, heat resistant materials without any problem.

(d) Drilling of small and deeper holes with very good quality of internal surface finish.

(e) Machining of cavities and holes of complicated and irregular shapes.

(f) It is used for making inclined and blind holes and finishing of conventionally machined surfaces.

Advantages of ECM Process: Following are the advantages of ECM process:

(a) Machining of hard and brittle material is possible with good quality of surface finish and dimensional accuracy.

(b) Complex shapes can also be easily machined.

(c) There is almost negligible tool wear so cost of tool making is only one time investment for mass production.

(d) There is no application of force, no direct contact between tool and work and no application of heat, so there is no scope of mechanical and thermal residual stresses in the work piece.

(e) Very close tolerances can be obtained.

Disadvantages and Limitations of ECM: There are some disadvantages and limitations of ECM process as listed below:

(a) All electricity non-conducting materials cannot be machined.

(b) Total material and work piece material should be chemically stable with the electrolyte solution.

‍(c) Designing and making tool is difficult but its life is long so recommended only for mass production.

(d) Accurate feed rate of tool is required to be maintained.

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