Short notes on Unconventional Machining Processes - Electro Chemical Grinding (ECG)
In this article series on Unconventional Machining Process, we now look at the next process, i.e. Electro Chemical Grinding (ECG).
Electro Chemical Grinding (ECG):
This process involves the use of a metallic grinding wheel and the process can be used for all the standard grinding operations, like surface grinding, internal grinding and face grinding etc. The specific use of this process is to grind such materials which cannot be shaped due to their extensive hardness or too high tensile strength. Some of such materials are carbides, hardened steels, stainless steel and some steel alloys.
The process consists of connecting the grinding wheel to negative terminal and the workpiece to the positive terminal. The power supply is of DC and provides an automatic voltage adjustment between 2 to 30 V. The coolant used int the process is an electrolyte, such as an aqueous solution of water-glass. The grinding wheel runs at a surface speed of about 1500 m/min. On the periphery of the grinding wheel are attached the abrasive particles which act as insulators, preventing a direct contact between the wheel and the workpiece. The electric current between the two flows through the electrolyte and the metal removal from the workpiece is through electrolytic action. The abrasive particles on the surface of the wheel remove the decomposed material to provide a fine surface finish and adequate dimensional control.
The grinding wheel is mounted on a spindle, which rotates inside suitable bearings. The workpiece is held on the machine table in suitable fixtures. The tables can be moved forward and backward to feed the work or to withdraw it. The grinding wheel and spindle are insulated from the rest of the machine by using an insulating sleeve. Electrolyte from the tank is pumped into the gap between the wheel and the workpiece. This leads to an electrochemical oxidation on the work surface.
Advantages of ECG:
- Negligible wear on the tool (grinding wheel).
- Work is free of surface cracks and distortion because heat is not generated in the process.
- Increased wheel life.
- For hard materials like cobalt, tungsten etc. the rate of metal removal is much higher than conventional grinding.
- As compared to conventional grinding, a very little cutting force is applied to the workpiece.
- Workpiece is not subject to any structural changes.
- A high dimensional accuracy of the order of 0.01 mm can be achieved.
- Considerable saving in wheel dressing time.
Disadvantages of ECG:
- High initial cost
- High power consumption
- In general grinding work, MRR is lower than conventional grinding.
- Only electrically conductive materials can be machined.
- Preventive measures are always required for corrosion against electrolyte.