"Joseph Gwinn" wrote in message
...
In article ,
"Ed Huntress" wrote:

"Ned Simmons" wrote in message
...
On Mon, 16 May 2011 21:18:41 -0400, Joseph Gwinn
wrote:

There was a recent article in Aviation Week saying that GE was using
Electric Discharge Machining (EDM) to rough out turbojet blisks
(combined rotor and blades) from Inconel 718, which is almost as hard
as
carbide. Apparently, GE got the idea in 2001 from the Chinese, who
were
using EDM for drilling of such alloys.

After roughing, the blisks are cut to final form using electro-chemical
machining, and also polished.

GE calls the technology "Blue Arc", the blue being the color of the
proprietary working fluid.

Joe Gwinn


Aviation Week, 9 May 2011, page 16, "Submerged Results - Novel
technique
speeds GE's blisk output", by Michael Mecham, The Inside Track
(column).

I have not found this on the web; I assume it's behind a paywall.

There are patents, however. Search for "electric discharge" and
inconel. I found applications 2010/0301016 and 0301017 for instance.

Something must have got lost in the reporting. Inconel 718 is nowhere
near as hard as carbide -- it's tough and gummy like most nickel
alloys, but not especially hard.

It did get lost. I don't think the reporter had much experience with any
of
this. The issue with EDMing Inconel is its high melting temperature. It's
a
little slow to EDM.


GE wouldn't need to learn from the Chinese about making holes with
EDM. I did quite a lot of work for GE's medium steam turbine division
in the mid to late 80's, and they were cutting tubine parts with some
pretty old conventional (sinker) EDM machines at that time, and the
press tools I was working on were cut with wire EDM. I believe much of
the work that was done on the sinkers was transitioned to laser
cutting not long after.

It has been interesting to hear the back stories, and the writer appears
to be in over his head.

It sounds like AvWeek needs a Machining Editor, Ed.

Joe Gwinn

They used to have one. A young engineer from McDonnell Douglas (Jerry
Mayfield) worked for us at _American Machinist_ for two years and learned
enough about manufacturing that _Aviation Week_ hired him away. He did a
good job for them for several years. I was covering advanced materials and
the aerospace industry at the time, and Jerry and I had a friendly rivalry
going over who could break stories first.

Then Jerry left, and for the next decade or so, they were out of luck. _AM_
moved out of the McGraw-Hill building, then was sold to Penton in Cleveland,
and AvWeek was on its own. I haven't been reading AvWeek for years, so I
don't know what's happened since.

BTW, there was an EDM machine tool builder, Raycon, based in Ann Arbor, MI,
that made most of its living building special machines for eroding those
cooling passages in turbine blades. It was a good chunk of business at the
time. There were three or four EDM companies, worldwide, that specialized in
it. They used wire-like electrodes made of some refractory metal (tungsten,
IIRC), burned with six or so of them at a time, and had automatic feeding
and trimming of the wire ends. They were very clever.

--
Ed Huntress