What is Wire EDM process???
EDM is known for Electrical Discharge Machining. Wire EDM is known as Wire Electrical Discharge Machining. The working principle, elements and applications are discussed below.
The working principle of Wire EDM is same as that of the conventional EDM except that it uses a small diameter as an electrode and deionized water as dielectric. The diameter of the wire is approximately 0.02 mm to 0.3 mm. A pulsed D C Supply is connected to the wire and the component. The component material is melted due to the heat generated from the spark as in case of the conventional Electrical Discharge Machining. In this Wire Electrical Discharge Machining method, a predefined gap between the tool and the component is maintained with the help of a CNC positioning system. CNC represents Computer Numerical Control. This is mainly used for machining of complicated shaped components.
Elements of Wire EDM-
The primary elements of Wire EDM system are as follows-
1. Power Supply
2. Dielectric System
3. Positioning System
4. Wire Drive System
These are the main elements of Wire EDM.
Power Supply System-
The power supply system of Wire EDM differs from conventional EDM only in two parameters, i.e., pulse frequency and current carrying capacity of the wire. This results in the reduced size of crater and hence better surface finish is obtained.
In Wire EDM process, deionized water can also be used as dielectric fluid instead of kerosene in conventional EDM. The advantages of water as Dielectric are as follows-
a. Ease of availability of water any where, any place, any time.
b. Desirable Thermal Properties.
c. Low viscosity.
d. Pollution free operation.
e. High material removal rate.
f. Better surface finish can be obtained.
g. Efficient flow properties.
Since the tool wear rate is higher, the wire cannot be reused. The effective way of supplying dielectric is by providing a stream of deionized water along the axis of the wire. The cost of the dielectric can be reduced by reusing it after through filtering. The filteration should be carried out with a 5 micro meters disposable filter paper. Some of the special additives are added to the fluid to prevent rust formation.
The positioning system of wire EDM comprises of two axes CNC table. When the wire approaches the component or any other material clogging the gap causes short circuit, this system will be effective enough to sense the condition in an adaptive control mode. The operating conditions are regained instantaneously.
Wire Drive system-
The principle requirements of this system is to provide fresh wire to the machining and to maintain the required tension such that the supplied wire is straight. As long as the supplied wire is straight with required tension, the taper, wire breakage and vibrational marks are reduced. The wire in this process is guided by wire guiders and it is passed through a series of tensioning rollers before it rolls in the take up reel. The wire guides are usually made up of diamond or sapphire.
Characteristics of Wire EDM-
1. Matte type of surface finish can be obtained in Wire EDM process.
2. The magnitude of the surface finish will be 0.1 micro meters.
3. The tolerance or the accuracy of Wire EDM is varies from +7 micro meters to -7 micro meters.
4. Maximum wire speed in Wire EDM process obtained is around 40 mm/s.
5. The machining rate obtained in Wire EDM process is 40 cm ^2/ hr.
Mechanism of metal removal-
The mechanism of metal removal in EDM process involves an electric erosion effect by the spark discharge. In this process, the metal is removed by repeated and small electric sparks between the tool and the work piece. THe spark is produced when a series of voltage pulses are applied across a small gap between the tool and the work piece. This results in the ionization of dielectric fluid. This tool is fed accurately to maintain the constant discharge gap by using a servo system.
Consider a relaxation type circuit of EDM. When the required voltage pulse is supplied, an electric field is produced between the tool, dielectric and work part. The free electrons from cathode are forced towards the anode due to the effect of electric field. The electrons while passing through this field collide with neutrally charged ions of dielectric medium. This results in separation of particles and causes ionization. The process continues till the ionization becomes a narrow channel through which continuous conduction of energy is formed. Due to this effect, a large amount of energy is liberated with high temperature of discharge. This high temperature discharge partially vaporizes the work piece and the dielectric. The metal pieces in the form of liquid are dispersed around the electrodes due to the high pressure of gaseous products in discharge. Hence, small craters are produced where discharge strikes on the work piece.
Applications of Wire EDM process-
1. Wire EDM process is used in fabrication of different types of dies such as extrusion, progressive, blanking and many more.
2. Machining of components which requires close tolerances can be machined using Wire EDM process.
3. Complex shaped components can be machined very easily in Wire EDM process.
4. Machining of narrow slots, key ways and mold components can be done in Wire EDM process.
5. Cutting of hardened materials such as poly crystalline diamond ( P.C.D ), cubic boron nitride ( C.B.N ), carbides and many more can be done in Wire EDM process.
6. Cutting of materials such as titanium, cast alloys and many more can be done in Wire EDM process, which are very difficult from other machining methods.
7. Tools used in forging and injection molding operations.
8. Delicate and thin sized components which are susceptible to the tool pressure.
9. Machining of medical and dental instruments can be done with the help of Wire EDM process.
10. Manufacturing of components used in electronic, defense and aerospace industries can be done with the help of Wire EDM process.
This is all about Wire EDM process.