15-11-2012, 06:13 PM
Electro chemical grinding
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Electro chemical grinding is one of the latest methods of grinding. This method is introduced in early 1970’s. In this process a grinding wheel in which an insulating abrasive is set in a conducting bonding material is employed. The D.C power required here is 5-15V. So for obtaining a voltage between 5 to 15V a step down transformer is used. The metal bonded abrasive wheel (or) the grinding wheel acts as a cathode. The work piece acts as anode. Very small distance is maintained between the anode and cathode.
An electrolyte is allowed to pass through the gap between the electrodes. The insulating abrasive particles get spread over the surface of the wheel. The height of the abrasive particles over the wheel in the gap between the electrodes indicates effective gap between the electrodes. The electrolysis can take place effectively in between this gap only. The current densities used are 2A/cm2 to 3A/cm2. The electrolyte that can be employed here shouldsatisfy the following properties.
1) High electrical conductivity
2) Low viscosity and high specific heat chemical stability.
3) Resistance to formation of passive film on work surface.
4) Non-corrosive and non-toxic in nature
5) Readily available and inexpensive
The electrolyte should perform many functions like
1) These should complete the electrical circuit between tool and work piece.
2) Electrolyte must allow all the desirable machining processes to occur.
3) It should function as a coolant by carrying away the heat generated during the chemical reactions.
4) Electrolyte should be effective in carrying away the products obtained by reactions in machining zone.
Removal of metal in ECG
Most of metal removal is done by electrochemical action. But some of the metal is also removed by the contact of abrasive particles to work piece. The abrasive particles have two main functions in electro chemical grinding.
1) To find the effective gap between the anode and cathode
2) To remove any passive layer formed over the work piece.
The metal removal rates in electro chemical grinding are of order 1.0m3/min/100A. But in general it is estimated as 0.5m3/min/100A.
Surface finish obtained by Electro chemical grinding
0.2 to 0.4 microns of plunge grinding can be expected for tungsten carbide tools. It is 0.4 to 0.5 microns in traverse grinding. For various alloys the surface finish is up to 0.4 to 0.6 microns can be easily obtained. If the alloy is hard then the surface finish will be high.
Accuracy of surface finish
Tolerances of order 0.01 mm can be easily obtained by employing electro chemical grinding. Even high accuracy can be obtained by removing required machining material in a single pass. If even high accuracies are required then most of metal should be removed in final pass with the same wheel by merely turning off the power supply.
Advantages of electro chemical grinding
1) Metal removal rate is very high.
2) Though the machine requires very high investment increased metal removal rate and less abrasive consumption acts as more than compensate for extra capital cost. On large scale production the cost per piece gets highly reduced.
3) Less risk of thermal damage as the heat generated is very low.
4) No presence of burrs on the finished surface.
5) High surface finish and no grinding scratches are present on the finish surface.
6) Pressure over the wheel due to work gets minimized.
Applications of electro chemical grinding
1) This process is extensively used for grinding carbide tools. Electro chemical grinding provides a savage of 75% in wheel cost and 50% in labor cost
2) Electro chemical grinding is also used for grinding fragile (or) very hard and tough materials.
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Electrochemical Grinding (ECG)
Electrochemical grinding combines electrical and chemical energy for metal removal with an EDM finish. It is a non-abrasive process and, therefore, produces precise cuts that are free of heat, stress, burrs and mechanical distortions. It is avariation on electrochemical machining that uses a conductive, rotating abrasive wheel. The chemical solution is forced between the wheel and the workpiece. The shape of the wheel determines the final shape.
It is a modern way of effective and speedy way of abbrasion and material removal. Burr free grinding is possible
The process involves when low-voltage, high-current dc power is applied between the grinding wheel and the workpiece in the presence of the electrolytic solution. With an electrolyte solution flowing to complete the electrochemical cell.
In this process the material oxidizes and the wheel can cut with the minimum stress thus eliminating any burrs. The process basically combines electrical and chemical energy for metal removal. It being a non-abrasive process produces precise cuts The best aspect of this kind is that the hardness and machinability have a lesser impact on the cutting tool. The process can be used for any conductive material.
Electrochemical grinding combines electrical and chemical energy for metal removal with an EDM finish. It is a non-abrasive process and, therefore, produces precise cuts that are free of heat, stress, burrs and mechanical distortions.
Norman Noble’s state-of-the-art electrochemical grinder can be used for micro precision machining of any electrochemically reactive and conductive material, including tough and specialty metals such as:
• Aluminum
• Amorphous metals
• Beryllium
• Beryllium Copper
• Copper
• Hastelloy®
• Inconel
• Iridium
• Nickel Aluminide