Hi again coyotebgone:
The EDM process relies on maintaining a gap between the workpiece and an electrode that is filled with a dielectric fluid who's function is to create just enough electrical resistance that electrons moving from electrode to workpiece or vise versa need enough current and voltage to generate a usefully powerful spark as they hop across the gap.
Maintaining the gap at the correct width and the correct dielectric strength is the whole art; it gets dirty with conductive particles which must be flushed out frequently, and the dielectric strength of the fluid in the gap changes continuously as the fluid is ionized and then recovers.
So there is sensing circuitry which decides when to stop advancing the electrode toward the work and permit the discharge of a current pulse to blow a bit of the workpiece away, and it decides based on the voltage across the gap.
As the burn gets deeper, the used fluid becomes more difficult to flush out and the performance suffers accordingly.
An additional complication is that as you change how much current to put into each pulse and how often, you also change how big the gap has to be and how rough the finish will be.
A modern sinker control will ask you for the finish you desire and the difference between the electrode size and the size of the cavity you want to cut, and will get there as quickly as it it can, continuously deciding how much power to put into each spark while still allowing the dielectric fluid to recover and be replenished, also making sure it never permits such a big spark as to intrude into the final part size.
So it starts out with high power at first and gradually winds down the power to give a fine finish.
In addition, since it needs a smaller gap for finishing, it also typically moves the electrode in small circles that get bigger and bigger as the power goes down, the gap gets smaller, and the finished size is approached.
So the electrode is deliberately made smaller than the shape it's going to produce and the size of the final electrode "orbit" determines how big the burn ends up.
A typical nominal orbit is 0.005" so the electrode is made 0.005" per side undersized but the actual electrode motion is not a circle of 0.005" radius... it's less than 0.005" by the width of the spark gap and that is always changing so you can see how complicated it all gets.
My machine, and others like it with "primitive controls" cannot do any of this automatically...you have to tell it what you want it to do and it just does that, regardless whether what you told it makes sense or not.
A fully adaptive control by contrast, asks what you want to end up with and then finds the best way to get there without you explicitly having to tell it anything about how to do it.
You will have to find a way to get what you want whenever you make a burn of any kind, and the deeper and narrower the burn, the harder it is to keep it going if you have to actually tell it which (of a half dozen different settings) to change as the spark gap conditions change.
That's what makes manual sinker work so challenging to do efficiently...you can do a burn in an hour on one day and fuck around for ten hours the next time on exactly the same burn, just because of some tiny flushing problem in an obscure corner of your electrode.
A modern fully featured sinker will never let such a condition develop in the first place, so they burn way faster and won't make your hair go grey, but they're complicated and cost a lot.
Cheers
Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining
