[AT] EDM

[Stephen Offiler]

That little video of the snowflake is really neat.  This is done with Wire
EDM.  Think of a sort of a bandsaw, whose blade is actually a very thin
wire (a few thousandths) and whose cut is done not with teeth but rather
with a highly controlled electrical arc.  The workpiece is on a table under
CNC control to move it very precisely, in 2 dimensions only.  It is not
fast.  That snowflake represents many hours in cut.  Given the amazingly
close fit, that was actually done with two completely separate workpieces.
If it was only one, it would look pretty similar but there would be a
"kerf" the size of the wire between inner and outer pieces.  To make the
interface completely disappear, they probably ground the surfaces of both
pieces together, and then with light coming from the right direction you
can't see the interface at all.

There's another type of EDM called "plunge" or "sinker" which can form
pockets with 3-dimensional features.  Instead of wire, it uses an electrode
that is the negative of the pocket shape, machined from graphite.  This is
how stamping dies and injection-mold tooling is made in the modern day.  A
version of the sinker was discussed a few weeks ago - with a cylindrical
electrode, used to drill holes and also to eat away broken taps.

SO


On Tue, Dec 10, 2019 at 1:37 AM Greg Hass <ghass at m3isp.com> wrote:

> I have heard they are amazing machines and have seen a little of the
> work they do. When they make a cut it is as smooth as glass and
> extremely accurate.  A guy at the coffee shop is part of a family that
> owns a tool and dye shop in Detroit that employs about 38 men. His kids
> now run most of the day to day operation although he keeps watch over
> some of it. He has now become a multi-million dollar hobby farmer. A
> couple of years ago he told me he still had a million and a half left to
> spend on the farm yet that year. Back on topic; he told me they have 3
> EDM machines
>   at the shop. The ones he has he said were $40,000 each when bought. He
> said consumables run about $18 an hour for each machine. He said you set
> them at night and then leave and they run till the job is done.
>                      Greg Hass
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