Electro-Discharge Machining (EDM) Process

Objectives1. To identify the process parameters of a die sinking EDM process

2. To study the features and operation of ZNC-EDM machine.

3. To investigate the effect of Ton on machining rate and overcut of a given working material.

Features of the EDM machine in the NTM laboratory

Electric discharge machining (EDM), sometimes colloquially also referred to as spark machining, spark eroding, burning, die sinking or wire erosion, is a manufacturing process whereby a desired shape is obtained using electrical discharges (sparks).Material is removed from the work piece by a series of rapidly recurring current discharges between two electrodes, separated by a dielectric liquid and subject to an electric voltage. One of the electrodes is called the tool-electrode, or simply the ‘tool’ or ‘electrode’, while the other is called the work piece-electrode, or ‘work piece’.

EDM is one of the most popular non-traditional machining process used in various industries. Any EDM Machine tool has four major components.

i. Power Supply: Power supply converts alternating current (AC) into pulsed direct current (DC) used to produce sparks between tool and work piece.

ii. Dielectric System: It consists of dielectric fluid, reservoir, filter, pump and delivery devices. A good dielectric Fluid should possess properties like;

high dielectric strength minimum possible time to breakdown when the breakdown

voltage is reached, effective cooling medium, Having high degree fluidity.

iii. Electrodes: Both the tool and work piece are electrodes in EDM. The material to be used as tool electrode should possess properties like machinability, low wear rate, good conductor of electricity.

iv. Servo System: A servo system is used to maintain a predetermined gap between tool and work piece. There is a gap voltage sensor in power supply, which sends signals to the servo system.

FIG: SCHEMATIC DIAGRAM OF EDM

Machine Name: ELECTRONICA, EZNC

SPECIFICATIONS X axis: 300mm

Y axis: 200mm

Z axis: 250mm

Maximum output: 200A

Work tank: 800x500x300 mm

Auto-parameter selection

Experimental Observations

Work piece thickness :0.42 mm Tool diameter :4mm Gap voltage : 45v Toff : 5 µsec Gap current: 5 amp Polarity:0.0

EXP NO

JOB WEIGHT(gm) MATERIAL REMOVED (gm)BEFORE AFTER

1 0.8052 0.79480.0104

2 0.7948 0.78580.009

3 0.7858 0.77680.009

Experimental results

Exp no TON (µsec)Machining Rate (MRR)

mg/secOvercut O.C

mm

1 10 0. 40.0234

2 20 0. 3461530.0279

3 30 0. 3461530.0351

5.00 10.00 15.00 20.00 25.00 30.00 35.000.34

0.35

0.36

0.37

0.38

0.39

0.4

0.41

Ton v/s Maching Rate

Pulse on time (µsec)

Mach

inin

g R

ate

(m

g/s

ec)

Exp no

Gap voltage (volt)

Peak currentIp(amp)

Tool diamete

rD(mm)

Hole diamete

rD(mm)

Machining time

T(sec)Ton Toff

1 45 5 4 4.0234 26 10 5

2 45 5 4 4.0279 26 20 5

3 45 5 4 4.0351 26 30 5

5 10 15 20 25 30 350

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

Ton v/s Overcut

Pulse On time (µsec)

Overc

ut

(mm

)

Conclusion

As the pulse on time increases, machining rate and overcut increases. With the increase of pulse current, the spark energy and consequently, the surface temperature of work piece rises, and material melting and MRR increase rapidly.