Electro-Chemical Machining

My experience is with medical devices and fuel injector bodies, not high temperature applications per se.

I would say that the improved surface finish provides less opportunities for non uniformities to be developed on the part surface. More consistent and therefore resistant layer.

Since this process would NOT be leaving metallic fines of abraded tool material, this is also less likely to initiate corrosion.

The electrolyte used is saline and providing it is compatible with the workpiece (duh-uh) and properly rinsed, I can't see any downsides.

(Unless You are a Green and think that the coal fired amperage used in the process is a threat to humanity. But that is another discussion)

Milo

Thanks Milo,

the South Island of New Zealand is 100% hydro so we are lucky here, but in other areas the discussion is certainly relevant and the waste stream is a concern too. It seems better dealt with these days, in fact could be better utilised than other forms of manufacture if done right. The process has a lot of benefits but...

We have seen issues with high temperature degradation and need to nail down the cause. There are a number of possible reasons for the degradation we see and this is only one of them. A number of articles I have found point to electro-polished components having higher rates of oxidation due to the lack of a compressive stress in the surface. This stress would be present with conventional machining and results in higher chromium mobility giving a better formed protective chromia scale, this may also be combined with selective chemical attack by electrochemical machining especially in the grain boundaries.

I was hoping someone may have had first-hand experience with this. I think we may be able to modify the process and/or the electrolyte used to minimise the problem.

You could do a DOE on high temp exposure on specially prepared samples using milled, ECM, and ECM Shot peened AND Milled Shot peened...

L8 taguchi matrix.

Have you confirmed it to be intergranular failure mode?

What is difference in MTBF (mean time between failures) between ECM and Non ECM Lots?

Milo

Thanks Milo,

the detail is too fine for shot-peening. Failure is internal oxidation, effectively the inability to form a tighty adherent and protective oxide on the surface, letting damage occur within the metal.

YES on working parts, But on test coupons as proxy for sensemaking.... Or Ballizing then.

http://www.ctemag.com/aa_pages/2009/0903_HoleFinishing.html

Look up Ballizing to put in a small degree of cold working strain...

Milo

The dies for briquetters used for molding hot briquetted iron (HBI) have pockets formed by ECM (that is the void where the briquette is formed).

HBI is briquetted at temperatures of between 600 and 700 degrees C with high specific pressing force. The dies are forgings made of tool steel - forgot exactly which one! The working face of the forgings are hardened to a depth of about 30mm prior to the ECM process being started.

The dies retain the steel characteristics and hardness after machining and subsequent use. No other process had been found to provide the same service or economy by the supplier - Koppern of Hattigen, Germany.

F/A-18 F404 Engine parts are Electro-Chem Machined, might be worth an E-mail to the manufacturer.