When applying the Electro-discharge Machining (EDM) manufacturing process the workpiece is machined either “sunk” into a specific fluid or not, the fluid which covers the workpiece in the cutting area being a dielectric.
The method which involves die-sinking uses a work table specifically made airtight (a sinking bath where the fluid is provided). The type of fluid most widely used is kerosene (petrol), distilled water or deionized water. This arrangement of the application of the EDM manufacturing process provides for the electrical discharge between the tool [electrode (-)] and the cathode (+), which in fact is the machined workpiece, to take place in dielectric fluid medium. The method features the following advantages and disadvantages:
1. The fact that the process takes place in a fluid medium improves the removal of metal chips from the cutting area and enhances cooling characteristics of the tool and workpiece.
2. Improved cooling and fast discharge resulting from switching off of the electrical impulse (frequency between 50 and 500 KHz) improves the wear resistance of the electrode (tool) and improves surface integrity (Ra) of the machined surface.
3. Due to the electrical discharge the process eliminates almost completely the emission of harmful gases into the atmosphere.
4. The process allows for “heavy” duty operation in higher frequency and current (A) values which results in increased process efficiency.
1. The presence of a work table, a bath tank, requires longer servicing time and impedes the process. When the workpiece is to be positioned onto the work table the tank has to be emptied of the contained fluid and the same happens when the machined part is to be removed from the work table.
2. Above requirements bring certain inconvenience during operation and involve higher energy consumption for filling in and pumping out the fluid from the tank. The machine itself becomes more complex in design and more expensive as it requires to be equipped with suitably designed units.
3. Removal of metal chips could in some cases be provided when machining blind holes such that chips are accumulated at the bottom of the vertical tool feed.
4. The presence of a large quantity of fluid, kerosene, in the machine in the operational area is a fire hazard. Special fire and explosion protection measures will be required for the machine and personnel.
5. When the WEDM method is to be applied for cutting operations the entire machine will be much more complicated requiring additional sealing for the wire (the electrode).
6. Applying the EDM method for turning lathes, grinding machines, etc. having horizontal work axis is not very easy as is the case for EDG (Electrical discharge grinding).
7. Applying the “orbital” processing technique is rather difficult.
8. The process provides poor visibility over the machined part for the operator to observe the process.
9. Item 8 above results in using mostly CNC control machines and equipment, which are in turn more complicated and expensive to use.