Electrochemical Grinding: Working Principle, Advantages, Diagram and more

In this post, you learn about electrochemical grinding, its working principle, advantages and more.

Electrochemical Grinding

Electrolyte grinding is a modification of both the grinding and electrochemical machining. In this process, machining is affected both by the grinding action and by the electrochemical process. Hence, in the true sense, it may be called ‘mechanically assisted electrochemical machining.

Working Principle of Electrochemical Grinding

In Electrochemical grinding, the metal bonded grinding wheel filled with a non-conductive abrasive. The grinding wheel act as a cathode and the workpiece is act as an anode. The electrolyte, which is usually sodium nitrate, sodium chloride, potassium nitrite, with a concentration of 0.150 to 0.300 kg/litre of water.

It is passed through a nozzle in the machining zone to complete the electrical connection between the anode and the cathode.

The work and wheel do not make contact with each other. Both are kept apart by the insulating abrasive particles which protrude from the face of the grinding wheel. A constant gap of 0.025 mm is maintained into which a stream of electrolyte is directed.

The electrolyte is carried past the work surface at high speed by the rotary action of the grinding wheel. With the rotation of the grinding wheel, metal is removed from the workpiece by the simultaneous electrolytic and abrasive action.

Abrasive grains on the surface of the wheel serve to act as a paddle which picks up the electrolyte and cause pressure to a build at the work area.

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The Wheel and Work Condition in Electrochemical Grinding

The electrolyte is captured in small cavities of semiconductive oxide between projecting nonconductive abrasives forming electrolytic cells. When these cells come in contact with the work the current flow from the wheel to the work and this leads to the electrochemical decomposition of work. The short-circuiting between the wheel and work is prevented due to point contact made by fine abrasive particles.

These protruding abrasive particles also remove the unactive layers formed on the work by abrasion to make the surface more receptive. It can be seen that the process is similar to conventional grinding. In that, an abrasive grinding wheel is used and the work is fed against the rotating wheel. In fact, 10% of the work metal is removed by abrasive cutting, and 90% by electrolytic action.

The grinding wheels used are of conventional shape and structure. Metal bond, diamond grit wheels are used for grinding tungsten carbide tips. Carbon bond wheels are used upon the hard alloy steels such as the stainless steels.

Wheel wear is negligible because the greatest part of the cutting action is electrolytic, and little dressing is necessary. The wheel, with its spindle and bearings, must be insulated from the machine frame and supplied with current through slip rings.

The machine is similar in design to surface grinder or tool. The cutter grinder and the equipment includes a tank, filter, and pump for the supply of electrolyte, and a power unit for delivering a heavy dc current. The current applied is in the range of 50 to 3000 A at 4 to 10 V (250 A/cm).

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Accuracy:

• Because there is very little abrasive action, Electrochemical grinding does not leave fine scratches which may impair the finish and leave stress raisers.
• Tolerances of about +0.02 are held on rather complex grinding operations. For closer tolerances, the proportion of material removed by abrasive should be increased.
• The surface finish is held in the range of 0.2 to 0.4 micron on carbide and 0.4 to 0.8 micron on steel.
• Sharp corners are difficult to obtain and the smallest radius of 0.2 mm cannot be avoided unless a final pass without electrolytic action is used.

Applications of Electrochemical Grinding:

Following are the Applications of Electrochemical Grinding:

• Any material which is conductive may be ground by the electrolytic process. But its most useful application is concerned with hardened steel, cemented carbides, and similar materials.
• This is mainly applied to resharpening and reconditioning of carbide tools and other materials that are difficult to grind.
• The grinding pressure is low. It is possible to grind and cut thin sections and thin-wall tubing of difficult materials without distortion or burr.

Advantages and Disadvantages of Electrochemical Grinding

Advantage

The greatest advantages are that all work is completely free of burrs. No heat is formed so no heat cracks or distortions are developed. Very little pressure is exerted on the work, and no wheel wear is found. Higher metal removal rates are possible, particularly upon hard materials.

Disadvantage

The major disadvantage is the cost of the ECG system. The metal removal rates are a low being of the order of 15 mm /s, and power consumption is high

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