Flushing is the key to efficient EDMing

• If the gap remains contaminated with debris the time it takes to prepare the gap for a spark may increase.
• This slowdown is sometimes referred to as (Ionization) Delay Time.
• Delay Time may vary dramatically from pulse to pulse, making your cut inefficient since it is actually adding non-cutting Off-Time to your burn.
• The cycle between each pulse (e.g.,Off-time + Delay Time) may vary producing fewer sparks per length of time.

For Energy Modelling of EDM Process please refer www.theijes.com/papers/v3-i2/Version-4/F0324024035.pdf or similar research findings.

It seems an interesting topic for research. I am in to more holistic view of energy consumption during EDM, but I found some interesting article you may also be interested if not you already read this.

I don't think there is an straightforward answer, as this should depend on material specific characteristics of the tool and the work. Since we are talking about micro-second level ON-OFF cycles, how many and how strong each individual spark could be highly variable depending on machining configurations.

Let me quote something;

"The material properties of the individual electrodes determine the fraction of input heat going into the electrodes. Theoretically, the steel anode should get a slightly lower share of the input power than the copper cathode

because the steel anode has a lower thermal diffusivity (k/pCp) than the copper

cathode. " 

Source: ANALYSIS OF SPARK PROFILES DURING EDM PROCESS by Shankar

http://www.tandfonline.com/doi/abs/10.1080/10940349708945647 

This article further shows how the input energy is shared among the anode, cathode and dielectric.

Again, this is a nice topic for research and I wish you best of luck.

One more article: Influence of EDM pulse energy on the surface integrity of martensitic steels (http://www.sciencedirect.com/science/article/pii/S092401369800082X)

http://www.tandfonline.com/doi/abs/10.1080/10940349708945647

Hello Jithin,

first I have to understand your question again. If you think should that during a pulse duration several discharges (sparks) can occur, then it can be gone assume that principle per pulse duration one discharge takes place. Under poor gap conditions, it may happen that the discharge collapses at this time and once again re-ignite. For ignition zero may still several streamer / leader exist which expire later than the channel formation and thus do not contribute to removal.

Where there are several discharges occur, then one would have to recognize it at the current and voltage waveforms, i.e. we would not have the unique courses with clear ignition, burning voltage and current peaks.

Govind, Gamage and Schulze, thank you for the answers

Hi , the question ("Range of number of sparks")is quite obscure to me but english is not my mother tongue.

However, I assume that by pulse cycle you mean tp (according to norm VDI 3402, i.e.ignition delay time td , discharge time te, off time to).

Now it depends if one machines in isopulse mode, where the discharge time te is kept constant, and the pulse frequency fp varies, or in isofrequency mode, where the pulse frequency is constant, and the discharge time varies.

In this second mode, I assume the answer to your question is: the range is from 0 to 100% of the pulse duration ti.

Usually there is one discharge per pulse. As Dr Schulze says, there can be re-openings during the discharge, so instead having one discharge one has many, with increase of electrode wear and lower MRR. The frequency of these reopenings depends on the regime, usually is about 1-2 MHz, so you can figure how many reopenings one has during ti.

High speed camera analysis has shown recently that in rare cases one can have two or three discharges per pulse at the same time, but this really the exception, and is quite a new finding to me.

Thank you for the supplementary answer. Perhaps more to the "simultaneous" discharges: The high-speed cameras have exposure times of 3 ns to 100 ns, ie we see on a screen the whole event in a time of, for example, 5 ns. During this period the last streamer / leader can go out and take place at a different location the discharge. This suggests a "simultaneous existence", but applies only to the Streamer. This effect is achieved primarily when the exposure times greater than 25 ns are (personal experience). Another effect is that all plasma phenomena have a kind of afterglow.

Thank you for this contribution, it is a good explanation!

can you tell me what is the approx. number of sparks produced per pulse? Also sir, is per pulse and per discharge has the same or different meaning in edm process?