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Electro Chemical Grinding (ECG)

Electro chemical grinding is also called electrolytic grinding. Metal is removed from the surface of the work piece by electro chemical action and also by abrasive action of a grinding wheel. 90% of metal is removed by electro chemical action and 10% of metal is removed by the abrasive action of the grinding wheel.

The equipment has a metal bonded grinding wheel. Brass, bronze and copper are bonded with abrasive grains in the grinding wheel. Diamond abrasive is used for grinding tungsten. Aluminium oxide abrasive is used for other metals.

The wheel is held in a horizontal spindle. The spindle is supported on insulated bearings. The work piece is held in a fixture against the grinding wheel. A gap of about 0.01mm is maintained between the wheel and the surface of the work piece. The work piece is connected to the positive terminal of a D.C. supply. The grinding wheel is connected to the negative terminal. 4 to 16V, 300 to 1000 Amps D.C supply is applied. A mixture of sodium chlorite, sodium chlorate or sodium nitrate and water is used as the electrolyte. The electrolytic solution is made to flow between the work piece and the grinding wheel. Electro chemical action takes place. Metal from surface of the work piece is removed in small particles. In addition to this, the rotating grinding wheel also removes metal from the work surface by abrasion. The small particles of metal removed from the work piece are carried away by the electrolyte. The electrolyte is collected in a reservoir. It is filtered and recirculated by a pump. Electrolyte also acts as coolant. The work piece is slowly fed towards the grinding wheel maintaining a constant gap between the work piece and the grinding wheel.

Applications:

· Used for machining hard materials which are conductive to electricity

· Used for grinding of tungsten carbide tool tips and hard steels.

· Used to grind thin section.

· Cylindrical grinding, form grinding, plunge grinding and surface grinding operations are done using this process.

· Used for machining refractory materials, high strength steels, nickel and cobalt base alloys etc.,

Advantages:

· Very fine finish is obtained

· Suitable for machining very hard materials like carbides. Carbides are difficult to machine by other processes.

· No heat is generated during the process.

· No distortion to the work piece

· No burrs are produced.

· Fast operation

· Thin materials can be ground without deflection as the grinding wheel does not press the work piece.

· Wheel wear is drastically reduced.

· No heat is generated so there is no danger of burning or heat distortion.

Disadvantages:

· This process can be used to machine only metals which are conductive.

· Sharp corners of the work piece cannot be machined.

· Electrolytic solution is corrosive.

· Initial cost of the equipment is high when equipped with larger power supplies.

· Intricate shapes may not be formed.

Modern Machining Processes:

In the past two decades some ultra hard and difficult to process of metals and alloys are not easy to manufacture, but continuous research on this field will produce rapid growth in this modern machining technology. The concept of material removal by Conventional edged tool machining is uneconomical for such harder and difficult to manufacturing materials and the degree of accuracy and surface finish attainable is poor. These edged tools machining involving plastic deformation and formation of chips has been known to man for several hundred years. The higher strength level would have a disastrous effect on the total machining bill if there was no corresponding improvement in machining technology. In view of the significance of this problem, Merchant (1960) highlighted the need for the development of newer concepts in metal machining; By adopting a integrated plan and utilizing the results of basic and applied research, it has now become possible to process some of the materials which were formerly considered to be unmachinable under normal conditions. Some of these methods have been commercially exploited while others are still in their experimental stages. The so developed newer machining processes are often called as “modern machining processes” or “unconventional machining processes”. The name unconventional implies that conventional tools are not engaged for metal cutting; rather energy is utilized in its direct form.

Modern machining processes are classified according to the type of fundamental machining energy employed, such as mechanical, electrochemical, chemical or thermoelectric.

Classification of Unconventional Machining Processes

Type of Energy	Metal Removal Mechanisms involved	Transfer Media	Energy Sources	Modern Manufacturing Process
Mechanical	Erosion	High velocity particles	Pneumatic/ hydraulic pressure	Abrasive Jet Machining (AJM), Ultra Sonic Machining (USM), Water Jet Machining (WJM)
Mechanical	Shear	Physical contact	Cutting tool	Conventional machining
Electrochemical	Ion displacement	Electrolyte	High current	Electro Chemical Machining (ECM), Electro Chemical Grinding (ECG)
Chemical	Ablative relation	Reactive environment	Corrosive agent	Chemical Machining (CHM)
Thermoelectric	Fusion	Hot gases Electrons	Ionized material High voltage	Ion Beam Machining (IBM), Plasma Arc Machining (PAM), Electro Discharge Machining (EDM)
	Vapourization	Radiation	Amplified light	Laser Beam Machining (LBM)
		Ion stream	Ionized material	Plasma Arc Machining (PAM)

PROCESS SELECTION

To make effective utilization of advanced machining methods, it is important to know the precise character of the machining issue. It is to be comprehended that:

(i) these methods cannot replace the conventional machining processes and

(ii) a particular machining method found suitable under the given conditions may not be equally efficient under different conditions.

A careful assortment of the procedure for a given machining issue is fundamental.

Before selecting the process to be employed, the following aspects must be studied:

(i) Physical parameters.

(ii) Properties of the work material and the shape to be machined.

(iii) Process capability.

(iv) Economic considerations.

When comparing the physical parameters of modern machining processes, it may be noticed that both EDM and USM require approximately the same power, whereas ECM consumes roughly forty times more power than EDM. ECM consumes much greater power, it is an excellent method for drilling long slender holes with length/dia ratio > 20. It can be seen that for the machining of electrically non-conducting materials, both ECM and EDM are unsuitable, whereas the mechanical methods can achieve the desired results.

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