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.

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.

--
Ned Simmons