In article ,
"Ed Huntress" wrote:

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

"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.

Their interest in the how of manufacturing appears to have declined, as
it seems that Jerry was not replaced. Did Jerry leave under his own
power?

I never knew what actually happened there.

I suspected as much.


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.

I always wondered how they drilled those passages. It was clear that
twist drills would be the hard way, to impossible.

By the way, how do they make the cooling passages in solid carbide
tools? Embed a piece of steel wire before compaction and sintering, and
dissolve the steel out with acid?

Ha! That's an interesting thought.

This is one of the growing list of things that I used to know, but forgot.
If you're really curious, call a company that makes carbide drills with
through-tool coolant and ask for an engineer. That's what I used to do.

I'll try that. Thanks.

My other method is the patent literature.

Joe Gwinn