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..

it is generally attributed to current density.