Electro chemical machining (ECM):
This process is generally used for hard materials which are difficult to machine using conventional methods. The process is used for mass production.
The removal of material takes place due to atomic dissolution of work material. Material removal rate is governed by Faraday laws of electrolysis. Material removal rate is quite high as compare to traditional machining methods.
An electrochemical cell is formed by the anode (workpiece) and the cathode (tool) and electrolyte flows in between them. The material is removed from work piece by electrochemical process. A very small gap (0.08 to 0.8 mm) is maintained between the tool (cathode) and workpiece (anode) through which an electrolyte (usually a neutral salt solution) is passed. The workpiece is kept stationary and tool is fed in a linear direction. A direct current is passed between the electrodes. When sufficient electrical energy is available, the positive charged metallic ions react with the negative ions present in electrolytic solution forming metallic hydroxides and other compounds. The positive ions moves towards the tool and negative ions moves towards the work piece. The material is dissolved with the formation of sludges and precipitates. The process continues till the tool has reproduced its shape in the workpiece. The material removed is pumped in the flowing electrolyte before being deposited on the tool. The electrolyte not only removes the product of machining but also removes the heat generated in the cutting zone.
The material to be machined should be electrically conductive. The material removal rate depends upon the atomic weight and valency of the work piece. The process is reverse of electroplating.
Generally Copper, Brass and Bronze are used to make tool.
A high surface finish of 0.2 to 1.5 microns can be obtained by this process. The machined surface is almost stressed free and without any thermal damage. Close tolerances can be obtained by this process.
No spark is produced in this process and the temperature generated is low so there are no metallurgical changes in the workpiece material.
The tool does not come in contact with the workpiece so there is no tool wear, giving a very long tool life.
A huge amount of energy is consumed during the process.
ECM is used for:
- Multiple hole Drilling
- Grinding of carbide tools and dies
- Die sinking
- Machining of steam turbine blades