re wear and polarity sorry i tend to rant and ramble when EDM is mentioned ;-)
On 03/03/2016 03:00 AM, Pete_Gruendeman wrote: > 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 > > > > > > ------------------------------------------------------------------------------ > > Site24x7 APM Insight: Get Deep Visibility > into Application Performance > > APM + > Mobile APM + RUM: Monitor 3 App instances at just > $35/Month > > Monitor end-to-end web > transactions and take corrective actions now > > Troubleshoot faster and improve end-user > experience. 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