Hi:
Besides any rules of thumb for estimating current, one is always looking
for the highest current that still allows stable erosion without exceeding the
carrying capacity of the fluid that is carrying away the debris from the site
of the erosion. If one exceeds that, then the gap gets contaminated and sparks
jump from electrode to debris and then make a deeper spot in the mold cavity.
And there are conditions where what amounts to re-cast can occur on the face of
the electrode, building up points and other unwanted features on the electrode.
I have seen this plenty of times on carbon electrodes. So-called graphite
electrodes are a mixture of carbon and copper (90/10 ranging up to 50/50)
sintered to make a solid. One popular trade name is Poco.
Only on rare occasions did I work with copper electrodes. They are more
expensive and are somewhat of a pain to machine as copper is gummy. Poor
surface finishes can be improved by polishing copper electrodes but it needs to
be done carefully without imbedding non-conductive abrasives in the copper. At
one time the Europeans and Japanese preferred copper electrodes and the
Americans preferred carbon. Machining carbon IS messy if you are messy. If
you are tidy then it's only somewhat messy.
I am seeing questions and suppositions posted here from people who seem to
have never run an EDM. Questions are good but knowledge provided by others is
not a substitute for the experience of running one. This is a different art
form than many people in metal working are familiar with. When you can, go run
an EDM; hang out with the people who do run them. With many metal cutting
operations, there are lessons from one machine that transfer to another. There
are commonalities between a bandsaw and a milling machine i.e. surface feet per
minute of the cutting tool and chip loading. Not so with EDM. This is a
different kind of animal.
Pete Gruendeman
--------------------------------------------
On Thu, 3/3/16, TJoseph Powderly <[email protected]> wrote:
Subject: Re: [Emc-developers] EDM gap control (Control parameters)
To: "EMC developers" <[email protected]>
Date: Thursday, March 3, 2016, 12:47 AM
50A/in^2
very crude rule fro Gr/St ( graphite to steel
)
the 'current
density' is NOT linear
maximum is near
400amperes even if area is yds^2
becasue the
process is not controllable at extreme currents
and is seemingly high at very low areas 50
amps supplied to 1mm dia
bras tube
and 12 amps 'draw' seen on meter
and that rule is only for
roughing ( creating net form )
not for
finishing
during roughing
the 'frontal area (Fp) is the governing factor
in finishing, the Peak to valley of the craters
is the governing factor
for engraving
graphite or copper is commonly used
the
choice is oftern determined by experience
experience of... do i want a
dirty shop and cheap electrodes ( graphite)
or a clean shop and expensive electrodes (
copper)
hth
tomp
On
03/03/2016 01:38 PM, Gene Heskett wrote:
> One thing I have always felt needed to be
asked, but don't recall
> seeing it
discussed, is when doing a sinker edm to imprint a carbon
> mold like I've seen pix of, like
engraving a relieved signature, is
>
there an optimum current per square, either in cm2 or in2 to
design
> the process to so it functions
best? And in terms of wear on the
>
shaped carbon electrode, is there a best current per square
in terms
> of the metal removed vs the
carbon wasted that will prolong the
>
electrode life vs metal removed? I've seen other
processes where
> optimizing one is not
optimizing the other. Or is there a better
> material to make the electrode from?
------------------------------------------------------------------------------
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. Signup Now!
http://pubads.g.doubleclick.net/gampad/clk?id=272487151&iu=/4140
_______________________________________________
Emc-developers mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/emc-developers
------------------------------------------------------------------------------
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. Signup Now!
http://pubads.g.doubleclick.net/gampad/clk?id=272487151&iu=/4140
_______________________________________________
Emc-developers mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/emc-developers
