After an initial increase till a value around 100 µs, does crater dimension remains almost constant or show slight reduction? If so, what is the reason behind it?
Dear Jithin,
The question has an answer positive according to my experience, or by other words, the crater dimensions will go to a constant value due to the plasma collapse for a particular pulse on-time. However, the interval of pulse on-time suffers changes with gap width, or by other words, the particular pulse on-time value changes with that.
José Duarte Marafona
Thanks for the reply José Duarte Marafona. It was very insightful.Could you please suggest me a reference for this behaviour of plasma? It would be very helpful.
I was looking for a graphical representation of variation of crater radius with increasing pulse on-time for single spark.
It is the number of cycles produced across the gap in one second. The higher the frequency, finer is the surface finish that can be obtained. With an increase of number of cycles per second, the length of the pulse on-time decreases. Short pulse on-times remove very little material and create smaller craters. This produces a smoother surface finish with less thermal damage to the workpiece. Pulse frequency is calculated by dividing 1000 by the total cycle time (pulse on-time + pulse off-time) in microseconds. Pulse Frequency (kHz) = 1000/Total cycle time (µs)
WIth increase in pulse on time, surface roughness increases gradually. i have experimented from 10 micro sec upto 400 microsecs and observed that SR increases gradually.
for your reference, the following may help you.
Amount of molten material which can be flushed away at the end of each discharge is dependent on the plasma flushing efficiency. Plasma flushing efficiency decreases as pulse on-time increases. The cause of this phenomenon could be justified by the reason that the increase in pulse on-time causes to decrease in the energy changing rate, as this causes a major increase in diameter while not much increase in the average temperature of the plasma channel, which leads to decrease in the pressure of the gap and its changing rate. So, regarding to the mechanism of bulk boiling phenomena, the amount of molten material, which is ejected from the molten material crater at the end of discharged, decreases . With the increase of pulse on time, the plasma channel becomes wider and positive ions become more active in attacking the cathode (work piece). This causes more melting and evaporation of the work piece, and leads to the increase of MRR. However, with further increase of pulse on time, due to thermodynamic and heat transfer issues, the energy transferred to work piece surface diminishes, and the material removal rate gradually loses its ascending trend and goes into a decline .
hope you will find it useful..
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