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Electrical discharge machining


#1

EDM is “electrical discharge machining”

Hot wire through butter analogy applies.

Basically the wire is highly charged and the electricity burns the
material away. I am not an expert, but a wire EDM looks like a band
saw with a hair width wire, electrically hot, and cooled immediately
with water so the wire doesn’t burn, kinda like kite fighting, move it
so fast it can’t get hot. We also do “plunge” EDM with a tool. You
can punch (burn) several holes at once and they call that "ganged"
EDM. The tool doesn’t wear because it is the electricity that burns
the metal away, not the tool.

Our “job shops” in the area are Meyer Tool and Douglas Machine.
Won’t be cost effective relative to a jewelers saw is my guess. Im
going for a walk! R.


#2

Ralph, My analogy of what an EDM spark is, is likened to lighting, and
the effect it has when it strikes an object, usually results in a
crater. In Wire EDM the wire is not really “hot” it is electrically
charged. Electrical energy produced by the power supply is applied
across the gap between the wire / electrode and the work piece. When
the machines servo moves the wire within “striking distance” to the
workpiece the die electric fluid provides a path for a spark to jump.
This high energy spark, through vaporization, melting and an
explosive effect, dislodges a minute particle of metal from the work
piece leaving a small crater. The dislodged particle is then
solidified and washed away by the die electric fluid. The wire /
electrode never comes in contact with the workpiece but due to the
above description of what is occurring the electrode degrades rapidly
and must be replaced with fresh electrode material. In a Wire EDM
operation it is replaced by the continuos feed of new wire, wire
diameters are from .004" to .012" in diameter and is basically a
brass based material. In plunge EDM it is replaced with a remachined
or a new electrode. EDM is not the answer to all production questions
but it can be a liberator to a huge amount of time used in sawing out
and a key word here is production, of multiple pieces. My Wire EDM
can run 24 / 7, how long can you saw. I have used the Wire EDM to
cut a large variety of materials tool steel, aluminum, titanium,
inconnel, cast, gold, graphite, silver, just so the material is
electrically conductive I can cut it. I have never cut any precious
metal with my plunge EDM, remember material is vaporized literally. I
can’t see anyone wanting to lose something that cost so much. It might
be caught in the filter, but recovery is another story.

If anyone has specific questions about EDM and how it can apply to a
job or up coming project and you would like to discuss applications
please contact me direct. Please visit my web site, it’s still under
construction, but the new EDM photos of a Wire in action should be
posted soon. If not email me and I’ll email you a pretty cool image.
Yes, I use my digital camera to keep my customers informed on their
work progress.

Kevin
www.Advantagetool.net


#3
    Basically the wire is highly charged and the electricity burns
the material away.  

It used to be called spark machining. Nearly 50 years ago I was
associated with a Cutlery Research Association, which began to
introduce EDM to the highly conservative cutlery trade in Sheffield
England. The concept is simple. An electrode, usually brass, can be
any shape and is electrically charged to a high potential. A piece
of metal, like steel (which may previously be completely hardened) is
the opposite electrode. A very hot fat spark is made to jump between
the two whilst completely immersed in a circulating kerosine bath.
The intense heat of the spark vapourises metal at the point of
contact, and the kerosine instantly carries away the vapour and cools
the metal. The spark is not continuous as it is supplied by a very
large bank of electrical capacitors which are being charged and
discharged through the electrodes at a fairly high frequency. On top
of this, the brass electrode is very close to the workpiece, but is
moved up and down as the spark is discharged. Using this principal
one may make holes or depressions in hardened steel and stainless
steel of any shape or size.

At an open day, the Association showed a brand new 12" bastard file
which had a piece of brass curtain rod of weird section making a nice
slide-fit through it. Another piece of hardened steel had a curved
square hole machined through it from a face to an edge - a square
hole curving through 90 degrees! They’d made several pairs of half
scissors in brass, and used these as electrodes to make new hardened
and tempered steel stamping dies for turning out steel scissors -
otherwise a craftsman would have had to laboriously carve out the
dies. It is, in a way, similar to arc cutting.

There is a drawback; electrical discharge machining is very slow, so
they set it up and leave it to work all day and night, and the brass
forming electrode has to be changed every so often as it too wears
away, but more slowly than the workpiece. Thus, a University
research establishment where I worked built one of these machines.
Only something went wrong in the middle of one night the building was
very badly damaged by the consequent fire. (Murphy’s Law states that
if anything can go wrong it will, and a corollary states that it will
occur at the worst possible time; e.g. water pipes burst at 3am on
Christmas morning) I don’t know for sure, but I have the impression
that spark machining doesn’t work too well wirh very conductive
metals, like silver, copper or aluminium. But it is marvellous for
making steel dies.

John Burgess; @John_Burgess2 of Mapua Nelson NZ


#4
 I don't know for sure, but I have the impression that spark
machining doesn't work too well wirh very conductive metals, like
silver, copper or aluminium. But it is marvellous for making steel
dies.  

Sorry to disagree but, modern electrical discharge machines work very
well in conductive materials. Also these are not the “spark” machines
of the past. But are highly technical computer controlled machines.
Regards, Kevin W. Advantage Tool & Microweld www.Advantagetool.net