Wire electric discharge machining

engineering

1. WIRE ELECTRIC DISCHARGE MACHINING Presented by: Sumaiya 17MEIM024 GE7142

2. Contents Wire electric discharge machining Working principle Wire EDM machines Wire types and their selections Stratified wire Benefits of stratified wire Process variables Process characteristics Applications

3. Wire electric discharge machining Wire electrical discharge machining (EDM) is a non-traditional machining process that uses electricity to cut any conductive material precisely and accurately with a thin, electrically charged copper or brass wire as an electrode

4. Principle of wire EDM The spark theory on a wire EDM is basically is same as that of the EDM process. In wire EDM, the conductive materials are machined with a series of electric discharges(sparks) that are produced between an accurately positioned moving wire(the electrode) and the work piece. High frequency pulses of ac or dc current is discharged from the wire to the work piece with a very small spark gap through an insulated dielectric fluid(deionized water)

5. Principle of wire EDM The heat of electrical spark estimated at around 15,000 to 21,000 Fahrenheit, erodes away a tiny bit of material that is vaporised and melted from the work piece(some of the wire material is also eroded away). These particles(chips) are flushed away from the cut with the stream of de-ionized water through the top and bottom flushing nozzles.

6. Major components of machines 1.Computerised numerical control (CNC) Think of this as BRAIN 2.Power supply provides energy to the spark 3.mechanical section worktable, work stand, taper unit, and wire drive mechanism. 4.Dielectric system the water reservoir where filtration, condition of water (resistivity/conductivity) and temperature of water is provided and maintained.

7. Wire types and their selection Selection of wire in wire EDM should be done by taking following criteria into consideration:- Tensile strength Fracture resistance Conductivity Vaporisation point(low is preferred)

8. Types of wires:- Copper wire Brass wire Coated or stratified wire Molybdenum wire

9. Stratified wire “if I need the tensile strength of one material and the conductivity or flush ability of another, why not coat or plate one with another?” Stratified wires have a wire core coated with one or more layer of different materials. Stratified wires usually consist of an alloy with low vaporisation temperature, plated to a higher tensile strength core.

10. Benefits of using stratified wire special coating to enhance cutting speeds and surface quality Designed to operate at higher speeds than traditional wire Surface quality will be much higher than traditional brass wire Wire burns extremely clean and has a very smooth wire surface.

11. Process variables Pulse duration Pulse interval Servo voltage Peak current Gap voltage Dielectric flow rate Wire feed rate Wire tension

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16. Process characteristics Surface roughness Material removal rate Kerf(width of cut) Wire wear ratio

17. Process characteristics SURFACE ROUGHNESS Surface roughness is greatly affected by pulse on time, peak current and cutting speed in WEDM. Among these pulse on time is found to be the most significant parameter affecting the surface roughness. MATERIAL REMOVAL RATE In WEDM the material erodes from the work piece by a series of discrete sparks between the work and the tool electrode immersed in the liquid dielectric medium. These electrical discharges melt and vaporize minute amounts of the work material, which are then ejected and flushed away by the dielectric fluid. MRR directly increases with increase in pulse on time (Ton) and peak current (IP) while decreases with increase in pulse off time (Toff) and servo voltage

18. Process characteristics KERF Kerf is one of the important performance measures in WEDM. Kerf is the measure of the amount of the material that is wasted during machining. It affects the dimensional accuracy of the finished part. Kerf of wire EDM work piece depends on gap voltage, pulse on time, pulse off time, wire feed and flushing pressure WIRE WEAR RATIO As WEDM is a thermo- electrical process in which material is eroded by a series of sparks between the work piece and the wire electrode, along with the work piece material some particles from wire also will erode, this phenomenon is called wire wear and this should be kept to a minimum. Wire failure occurs in wire-EDM process as a result of severity in wire wear rate, which is a function of discharge current and discharge time

19. Applications of wire EDM The process is used in the following areas:- Aerospace, medical, electronics and semiconductors applications Tool and die making industries For cutting hard extrusion dies In making fixtures, gauges and cams Cutting of gears, strippers, punches and dies Manufacturing hard electrodes Manufacturing micro-tooling for micro-EDM, micro-USM and other such micro machining applications

20. THANKYOU!