OCTOBER 19-20, 2012 - YMCA University of Science & Technology

Proceedings of the National Conference on
Trends and Advances in Mechanical Engineering,
YMCA University of Science & Technology, Faridabad, Haryana, Oct 19-20, 2012
Figure No. 1
Figure No. 2
Increase in peak current higher over a certain limit, leads to arcing, which decrease discharge number and
machining efficiency .Subsequently wire to be break down because of short pulse off time .The removal time of
debris particles from the gap become insufficient. But from figure no. 2, with increase of pulse off time along
with pulse on time , maximum cutting speed occurs which is due to complete flushing of debris particles and
available a complete deionized fluid for the next discharge . But further increase of discharge current will leads
to increase of cutting speed. Maximum cutting speed of Nimonic 90 with present machine tool occurs at
discharge current 200 Amp with pulse off time (Toff) 45μs.
3.2. Effect of pulse-on time
The effect of pulse on time (Pulse duration) on cutting speed is shown in figure no. 3 for two setting of Toff =35
and Toff =40 .The other parameters were kept constant under the condition of peak current 120 μs, Servo voltage
20 V, Wire feed 5 meters /min, Wire Tension 10 N, Dielectric flow rate 10 liters per min. and servo feed 2080.
The cutting speed increases continuously with increase of Pulse on Time. The machining becomes unstable at
high pulse duration. At high discharge energy, the amount of debris in the gap becomes too great which form an
electrically conductive path between the electrode and workpiece, resulting into development of unwanted arc
between them. If we increase the pulse off time with increase of pulse duration time, we can provide more time
to flush away the debris. Maximum cutting speed of Nimonic 90 with present machine tool occurs at pulse on
time (Ton) 118 μs with pulse off time (Toff) 40 μs.
3.3. Effect of pulse off time
Figure no. 4 shows the effect of pulse off duration for two machining setting Ton 108µs and 120μs with fixed
variables discharge current 120 A ,servo voltage 20 V, dielectric flow rate 10 liter per min and servo feed 2080
and wire feed 5meters per min, Wire Tension 10. The cutting speed increases with increases in pulse off time 25
to 45μs and after that it decrease sharply decrease with increase in pulse off time.
513