Re: Re[1]: wire edm info
Posted by
ballendo@y...
on 2000-11-05 21:09:38 UTC
Ian,
I'm not speaking from empirical experience here. Just "book" learning.
I don't believe commercial EDM's have to "back up" a few steps. This
would seem a very difficult proposition, and also unnecesary.(only
required if feedrate exceeds cut rate, and wire strength :-) )
The "commercial" edm cycle is: 1) advance (into contact with
material),2) blast electrons until contact is gone/reduced (as
determined by system/circuit feedback), 3) Repeat.
Now, If some arbitrary feed rate is selected, and does not operate
with "feedback", THEN you may need to "back up" because your initial
move exceeded your ability to cut.
If the "cutting ability" of the EDM circuit is EXACTLY matched to the
available feedrate(s), there is no need for feedback. Since this
almost NEVER happens (and IS variable within the material), feedback
is a MUST for effective EDM.
If we are over cutting (our feed lags behind the cut) we have poor
cut quality (as the electrons blast in one place too long). If we are
under cutting (cut lags behind feed), we run the risk of breaking the
wire, or straining the machine.
Two variables are available to us to keep this system in balance.
Current and feedrate. One or both of these is controlled to give good
results.
The "Langlois" machine uses feedrate as the primary control, and
DOES "back up" as you have explained(previous posts). Since it is
a "sinker" type(straight line, one axis)EDM, this is no problem.
Except, as Jon E pointed out(and you experienced)the system is SLOWer
than it "could" be.
As the short conclusion to this long post, I believe you will find
better results by focusing on EFFECTIVE control/feedback of current
and adjusting feedrate(forward only) to match; rather than attempting
to implement the "Langlois" approach with wire.
Hope this helps.
Ballendo
I'm not speaking from empirical experience here. Just "book" learning.
I don't believe commercial EDM's have to "back up" a few steps. This
would seem a very difficult proposition, and also unnecesary.(only
required if feedrate exceeds cut rate, and wire strength :-) )
The "commercial" edm cycle is: 1) advance (into contact with
material),2) blast electrons until contact is gone/reduced (as
determined by system/circuit feedback), 3) Repeat.
Now, If some arbitrary feed rate is selected, and does not operate
with "feedback", THEN you may need to "back up" because your initial
move exceeded your ability to cut.
If the "cutting ability" of the EDM circuit is EXACTLY matched to the
available feedrate(s), there is no need for feedback. Since this
almost NEVER happens (and IS variable within the material), feedback
is a MUST for effective EDM.
If we are over cutting (our feed lags behind the cut) we have poor
cut quality (as the electrons blast in one place too long). If we are
under cutting (cut lags behind feed), we run the risk of breaking the
wire, or straining the machine.
Two variables are available to us to keep this system in balance.
Current and feedrate. One or both of these is controlled to give good
results.
The "Langlois" machine uses feedrate as the primary control, and
DOES "back up" as you have explained(previous posts). Since it is
a "sinker" type(straight line, one axis)EDM, this is no problem.
Except, as Jon E pointed out(and you experienced)the system is SLOWer
than it "could" be.
As the short conclusion to this long post, I believe you will find
better results by focusing on EFFECTIVE control/feedback of current
and adjusting feedrate(forward only) to match; rather than attempting
to implement the "Langlois" approach with wire.
Hope this helps.
Ballendo
>There is some useful information here. The biggest problem I have
>with wire EDM is understanding how the feedback circuits work and
>link into the CNC part of the machine.<s>
>To do this, presumably, the CNC part of the setup must have a way of
>remembering the exact cut direction for the previous few steps so it
>can back away from the cut in this same direction without the wire
>shorting onto the sides of the cut
>Ian