Anybody familiar with ECM, or Electro-Chemical Machining?

[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.

[ddmckee54]

I've started gathering the required "STUFF" to put together the test rig.  I've got my original Sunhokey 3D printer that has been unused since I got my D6 clone and the MP10, that will be the basis of the rig.  I got a cheap, $10, 12VDC peristaltic aquarium dosing pump to power the "jet".  And I got some blunt 14G hypodermic needles to be the actual jet nozzle.  I think the pack of 10 needles and 3cc syringes was also about $10. 

If this project doesn't work out, I'll still got a lifetime supply of micro oilers/glue injectors.  Don't know what I'd do with the pump though, maybe a working water cannon for the RC Benchy?

[ddmckee54]

More stuff was delivered today, but it's one step forward and two steps back.  I got the silicon tubing for the electrolyte return to tank line. 

Ebay claims the silicon supply tubing was delivered too.  Maybe it was delivered, but not to my house.  We'll wait a couple of days and see what happens, maybe it'll show up. 

The power supply that I ordered was delivered, but somewhere in its' travels it took a serious hit.  The case is mangled on the terminal strip end to the point that you can't even open the finger-safe terminal protector.  I've started a return on that one.  I mean it's a solid state power supply, so it should be OK, and I can straighten the aluminum case, but still...

[vtsteam]

Don, I've got my fair share of inadequate packaging from that big river company. On the other hand sometimes I get a giant box with something a tenth the size in it and lots of brown paper. Bummer about the power supply.  What size and type is it?

[ddmckee54]

It's a Chinese clone made by a company that apparently has no name.  I contacted the seller and he told me to do what was needed to see if it's even functional, then we'd discuss either a partial refund or a replacement.  When this thing hit, it hit hard enough that not only was one corner of the case folded over, the entire bottom of the case was racked out of square.

It's supposed to be a 36V/15A power supply, and when wired up it does crank out a nominal 36 volts with no load.  I couldn't think of anything that I could use as a load.  At least I couldn't think of anything that wouldn't potentially get me nominated for a Darwin Award.

[vtsteam]

If you're in the U.S. and 120V is your standard, do you have any incandescent light bulbs left? If you do, It won't light them much, but will present a load. Nowhere near 15 amps, but something.

An old corded 120V electric drill with brushes will also run on DC, again not at full power with only 36 volts, but it will run.

[ddmckee54]

I've got a couple of replacement bulbs for a stand mounted work light, they'd be about a KW's worth of load.  They were one of the ideas that I figured might get me nominated for a Darwin award, since they have such an unusual mounting base.  I've replaced the original fixtures with an LED work light from HF.  The heat from that KW worth of light would really heat up a small area, the LED runs MUCH cooler.

[vtsteam]

Don, you have a 1 kW incandescent work light bulb? That's kind of amazing in itself! You don't have, or cannot get access to say, a 100 watt 120V light bulb?

Well no matter what 120V incandescent bulb you use, it won't be drawing its rated wattage at 36 volts. If you're worried about draw, and your supply isn't constant current capable, or over-current protected, you can always put a 10 amp fuse in line with the test rig.

Honestly, if you're really worried about getting a Darwin award when connecting a household light bulb as a test load to a 36 volt power supply, why are you DIYing an ECM? Just think, exposed metals, electrodes, electrolytes....etc.

[ddmckee54]

I've got a work light that used a pair of 120V/500W Halogen rough duty bulbs, I think I've had that thing for 20 years at least.  The  bulbs are tiny little things actually, only about 10mm OD by 120mm long - with a contact clip on each end. 

I'm not worried about getting a Darwin award.  I really worry about what would my former engineering colleagues and electrician friends think when they read the story in the newspaper titled "Retired Electrical Engineer found electrocuted by light bulb?"

I'm not concerned about the ECM experiment, because it will be less dangerous than using a welder.  And I currently have 4 of those; a one-owner 50 year old Craftsman 200A AC/DC stick welder, an Eastwood 140A DC Mig, an Eastwood 140A DC Tig, and an Andrelli 140A AC/DC Tig.

[vtsteam]

Well, sounds good, I took you at your word about worries! Also, halogen bulbs not what I think you should try for a load. I meant strictly incandescent tungsten every-day light bulbs. Or used to be "every day".

BTW I've run corded brush type 120V electric drills on un-regulated DC from a car alternator in the past. There used to be a little black box device you could buy in the '70's which just bypassed the regulator on a pickup truck, and the instructions said to run the engine idle up to the point where a neon bulb lit.

The bulb was wired to light over 100V. The box had an outlet, and a circuit breaker, the bulb and just some pioint to point wiring, but no circuit board or active components. Brush type 120V corded tools generally had what were called "universal  motors" which ran on DC as well as AC. In fact I copied the circuitry back then and made a generator from a horizontal shaft Briggs and Stratton motor and a car alternator, and it ran all kinds of power tools, including a circular saw, and a hedge trimmer.

Anyway, for those type motors, lower voltage DC will just run them slower, which was why I suggested it. Don't try to use them to do work at 36 volts, and you should be well under your 15 amp supply limit.

But again do nothing if you are in the least worried -- I write this not as a recommendation, just giving my own experience. There are dangers involved, yes, if one is inexperienced at this level of electrical DIY. Also be aware that DC is more dangerous than AC and 36 volts is above the threshold of possibly fatal consequences.

[ddmckee54]

Yeah, it only takes a few mA under the wrong conditions. 

My 5mm ID supply tubing was finally found, order tracking said it was delivered on the 5th - but I couldn't find it.  I finally found the USPS tracking number and talked to the Post Office.  The mailman knew he'd delivered two packages that day.  We got to looking around and found it in a remote corner of the porch, under some wind blown leaves. 

The power supply seller and I finally agreed on a partial refund amount.  So I'll probably just put it into service, if it dies - it dies.

Now I need to kick the tires on my old Sunhokey 3D printer and see if there's any life left in it.  I think the last time I actually used it was pre-covid.

Don

[ddmckee54]

I spent some time with my friend Google last night.  In found a couple of interesting research papers on Electro-chemical Jet Machining.  One was investigating cutting a Japanese grade of 304 stainless, SUS304. I THINK the other was looking at cutting an aluminum/titanium/boron alloy, TiB7050?

Being good research papers they both listed the parameters used in their experiments.  I was particularly interested in the differences between their single pass cuts in the two materials.  A single pass on the SS only cut about 20-30 microns deep with a feed rate of less than 1mm/minute.  The aluminum alloy on the other hand was a whole 'nuther ball game, a single pass cut about 600 microns deep with a feed rate of 30mm/minute.  The author of that paper remarked that you could practically see the excavated material being conveyed away.

I haven't found anything on cutting a more normal steel yet, although I did see a video of ECM being used to rifle pistol barrels.  The entire rifling  process, from cycle start to complete, took less than a minute.