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Anybody familiar with ECM, or Electro-Chemical Machining?

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ddmckee54:
Any body here familiar with a process called ECM?  It's similar to EDM only instead of using high voltage and a di-electric fluid like EDM uses to blow little bitty pieces off the part - ECM uses relatively low voltage, a conductive fluid, and electrolysis to chemically erode the pieces off the part.

I am doing RC conversions of Bruder construction equipment and would like to build metal versions of some of the parts.  Unfortunately I have neither the skill to make the parts by hand, nor the extra funds that would be required for the necessary CNC equipment, wire EDM, high-powered fiber laser, or something similar.  What I do have is an unused FDM 3D printer which can probably be adapted to a CNC ECM cutter for any conductive metal using water and a little salt.  I've seen 2-4 year old videos on YouTube that show it's possible.  It's a slow process - but possible, and the cut quality I saw is nothing to write home about.  But they do work as a proof of concept.

awemawson:
Sounds like one step up from etching PCBs for circuits where just a mask and etching fluid ( I used to use Ferric Chloride) is used.

There used to be a marking system for tools that used saline solution, a low voltage, and a mask produced on a typewriter (wax coated paper) that was a form of ECM.

Modellers of small scale engines and rolling stock use ECM to form chassis rails from circa 3mm brass by a similar process.

David Jupp:
Think about how you'll dispose of the resulting liquid effluent.

I know of a company that did a lot of ECM to make a particular product - it ended up with a large stock of difficult/expensive to dispose of waste resulting from the process.

ddmckee54:
A couple of the articles I've seen use a salt-water solution as the etching solution, here's a couple of links:
https://www.youtube.com/watch?v=x4m1RWWJElM
http://amosdudley.com/weblog/blog/

I'm not talking about a company doing mass production.  So instead of hundreds, or thousands, of liters of effluent - I'd be dealing with a few liters of contaminated saltwater.  The saltwater could be safely evaporated leaving you with at most tens of grams of dry powder, containing mostly salt.  Aluminum and mild steel would be fairly safe to work with, generating mostly insoluble compounds.  However, Amos Dudley in the link listed above recommends to avoid any alloys containing chromium, like stainless steel.  Since one of the byproducts of a chromium containing alloy might be hexavalent chromium.  So I will definitely NOT be cutting stainless steel, or any chrome plated bumpers.

vtsteam:
I've etched reed valves out of thin spring steel by spray painting a mask, then electro etching. It's one of the few ways you can get a complex shape cut in this material. The process is mainly suitable for very thin materials, because the sides start to etch in if thicker. You can use any salt, sodium carbonate works, as it does in de-rusting via electolysis. Same principle. You don't need acids or heavy duty chemicals that industry uses to speed production.

This kind of electrolysis is no more polluting than letting the same steel rust, and the quantities we create in a hobby shop are miniscule. Driving an automobile to the grocery store in the rain probably equals the entire lifetime polluting output of very occasionally electro etching a small hobby part from steel or aluminum in a backyard shed. Likewise the steel tanker that delivered the auto's oil, the offshore rigs, all suffer massive electrolysis of numerous kinds of metals. The there's batteries in electric cars......well, nevermind. Let's keep a sense of proportion in mind.

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