Hi Nicklaus and TJ:
It's true that too close is 1-2 microns for a finish burn and too far is
the same. My machine resolves 40,000 encoder counts per inch so 1-2 microns
works out to 1.6 to 3.2 encoder counts, which you will travel over in 1.6- 3.2
thousands of a second, fast enough I would think. Pulse rates are upwards of a
few thousand per second so we're really talking about 2- 5 pulses, less on a
roughing burn which has less pulses per second and longer sparks so electrode
positioning is not as critical. Any machine can produce acceptable roughing
burns. Only a well tuned and properly working machine can produce the finest
finishes.
It's also true what TJ said about electrode wear, that it's greatest during
a finish burn and lowest during a roughing burn. Negative polarity on the
electrode causes greater electrode wear (other settings being the same) but
that extra wear is often allowed to get acceptable erosion during difficult
conditions, or when metal removal rates are more important than reducing
electrode wear. Hole poppers would be an example of this -- I think, though I
have not run one myself. Polarity and electrode wear are important to the EDM
operator but are meaningless to the motion control software.
Pete Gruendeman
--------------------------------------------
On Wed, 3/2/16, TJoseph Powderly <[email protected]> wrote:
Subject: Re: [Emc-developers] EDM gap control (Control parameters)
To: "EMC developers" <[email protected]>
Date: Wednesday, March 2, 2016, 9:29 AM
Nicklaus hello
even tho the average velocity is low
it is important to move to the correct position
as soon as possible
if the tool is too
close
it will cause thousands of bad
discharges per second
and damage the
stock
( velocity is NOT important, position
IS important)
if the tool is too far away
then many pulses will not occur
wasting time in a process that is already
slow
too close is -1 or 2 microns
too far is + 1 or 2 microns
more positional error is just bad control
MRR is metal removal rate
measured in grains per minute or grains per
hour
the finer the finish
the slower the MRR
MRR is higher with
rougher surface, lower with finer
Vw is
VerschleissWerkstuffe or loss of workpeice
Ve is VerschleissElekgtrode or loss of
tool
Vw is high for
roughing (schruppen) and Ve is low for roughing
Ve is high for finishing ( schlicten) and Vw is
low for finishing
there is
a point where it is advantageous to reverse the polarity to
get
better Vw an Ve
This
point is related mostly to on time and D%, not current ( tho
this
point is usually at low currents)
back to your post...
yes the velocity is slow
no the
position update should not be slow
run the position update as fast as you can
even use hardware to update the motor amplifier
and only let Linuxcnc
monitor postion
just to make the position loop as fast as
possible
tomp
On 03/02/2016 06:12 PM, Nicklas Karlsson
wrote:
>> ...
>>
All of this start, stop, backup motion will result in an
average rate of travel that is on the order of inches per
hour. It's not fast. Though the positioning rate for
forward and reverse motion can be inches per minute.
>> ...
> Then it is so
slow as at maximum inches per minute there is no point with
position/velocity loop faster than once each millisecond?
>
> For Z-axis there
would be no problem with 40kHz servo loop if needed.
>
> Regards Nicklas
Karlsson
>
>
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