23 January 2017

Electrochemical Grinding

Electro-chemical grinding is also called electrolyte 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 electro-chemical process. Hence, it may also be called mechanically assisted electrochemical machining.

Electrochemical Grinding
In ECG the metal bonded grinding wheel impregnated with a non-conductive abrasive is made the cathode and the workpiece the anode as in ECM.
The electrolyte which is usually sodium nitrate, sodium chloride, sodium nitrite, potassium nitrite with a concentration of 0.150 to 0.300 kg/litre of water, is passed through a nozzle in the machining zone in order to complete the electrical bridge between anode and cathode.
The work and wheel do not make contact with each other because they are kept apart by the insulating abrasive particles which protrude from the face of the grinding wheel.
The electrolyte is carried past the work surface at high speed by the rotary action of the grinding wheel. metal is removed from the workpiece by the simultaneous electrolytic and abrasive action.

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 is removed by abrasive cutting and 90% by electrolytic action.

The grinding wheel used are 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. 

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

Accuracy :
  • Tolerance is about +0.02 to -0.02 are held on the rather complex grinding operation.
  • For closer tolerances, the proportion of material removed by abrasive should be increase.
  • Surface finish is held in a range of 0.2 to 0.4 micron on carbide and 0.4 to 0.8 micron on steel.
  • A sharp corner is difficult to obtain and minimum radius of 0.2 mm.
Applications :
  • Any material which is electrically conductive may be ground by the electrolytic process.
  • Mainly used for resharpening and reconditioning of carbide tools and other materials that are hard to grind.
  • Grind and cut thin sections
  • Grind difficult materials without distortion or burr.