Author Topic: Electroforming/electrotyping  (Read 4945 times)

Offline sorveltaja

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Re: Electroforming/electrotyping
« Reply #15 on: February 26, 2019, 07:52:05 PM »
Here is the result after 28 hour 'marathon'. First 14 hours at 300mA 2,5V, and then another 14 hours at 400mA 3,3V. As it appears, resulting object is still attached to silicone mold. But why all the crossing wires?

They are only needed for one thing - in the beginning, after the mold has been 'blackleaded' or covered with graphite powder, there should be electrical "contacting points", that are in contact with graphite layer, to start copper formation. It should be done at very low amperage, about 30-50mA.

Graphite isn't exactly a good conductor, being more like resistor, so it can't handle high current without popping like fuse. But once the graphite layer is covered with copper, more amperage can be applied.
In the above picture, formation at lower left is an indication of too much current/not enough agitation. That copper layer seems to expand wildly, and needs to be more controlled.

But after all, some of those crossing wires, being 0,5mm wire at the beginning, became so thick and hard, that I couldn't cut them with electronics pliers.

Then the measurement, after the resulting object was released from the mold. The target part of the result was a bit of disappointment, as it is only 0,2mm thick.
Surrounding areas measured as much as ~1mm thickness - exactly opposite results to what I'm after .



Last but not least, is the more important surface, straight out of the mold, which has graphite powder embedded to it. Some say it's more like an "authentic" look, though it's easily buffed away, to bring out the bare metal:


Offline b.lindsey

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Re: Electroforming/electrotyping
« Reply #16 on: February 26, 2019, 09:24:06 PM »
Interesting stuff. How are the wires attached to the thin graphite layer?

Bill

Offline sorveltaja

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Re: Electroforming/electrotyping
« Reply #17 on: February 27, 2019, 09:05:01 PM »
Bill, to start, some turpentine is applied to cover areas, where graphite powder is to be added later. Graphite powder sticks without turpentine as well, but tends to release loose powder, that end up floating in the electrolyte, when submerged first time:   


Then the graphite powder is applied to the mold:


Next comes the "wire cage". Any copper, or tin plated copper wire is suitable, as long as it's thick enough to poke through the mold. I use 0,5mm, tin plated electrical wire, because I have whole spool of it. It has to be stripped though. Enough of it is used to make the cage, and a hook to hang it in the bath:


After that, 'contact points' are made by brushing some more of graphite powder to areas, where wires go through the mold:


And this is how the copper layer starts to develop, after 15 minutes in the bath:

Offline Vixen

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Re: Electroforming/electrotyping
« Reply #18 on: February 27, 2019, 11:29:41 PM »
I am very interested in your electroforming process and experiments. I am impressed with the surface detail you are achieving. I notice you are having difficulty in achieving any useful shell thickness inside the mold. The majority of the material growth appears to be on the wire cage and on the periphery, only a very small proportion is being deposited on the target area.

Could it be that the wire cage is shielding the mold area by drawing all the copper deposition to itself rather than to the mold surface? Is it necessary to have the wire cage in front of the mold? Could the wire cage still act as the 'contacting points', if it were repositioned at the rear of the mold facing away from you copper anode bag?

Many years ago, I served with the Royal Air Force at a large RAF Maintenance Depot in South East Asia. I was given a job in the electroplating shop for a couple of weeks while the regular guy was on leave of absence. I had no particular skills to offer, I was simply standing in the wrong place at the wrong time. The electroplating shop was there to make repairs to aircraft and radar waveguide components. However, there was an illegal sideline for private work. We called them 'Rabbits' because of the speed with which things disappeared from sight whenever the bosses appeared.

Silver plated sports trophies, which tarnished quickly in the tropical heat, were a regular source of illicit income. They did not need  (or get) a thick layer of electro plated silver, just a quick 'flash coat' was enough to make them look like new again.The silver of adequate quality for the anode was cheaply available from jewelry bought in the local market. However the sports trophies were difficult things to electroplate evenly due to the cup like shape. We made a special plating bath just for 'flash coating' these silver cups. The method we used may?? have something to offer for electroforming.

The guy in charge explained that the electroplating always formed on the surface closest to the anode,where the current density was greatest. and never on the far side of the object where the current density was very low. To overcome this problem the object to be plated could be rotated to achieve a more even deposit. A better way was to surround the cup with a circle of interconnected anodes all suspended at about the same distance from the trophy. Agitating the electrolyte also helps. In this way we could quickly re-plate the outside surfaces of the  tarnished sports trophies. The inside of the cup never received any plating, being shielded by the proximity of the outer surfaces to the anodes.

To plate the inside of the cup, it was necessary to suspend a silver chain anode down the center line of the cup, until it almost touched the bottom, but not quite. The current density was then uniform all round the silver chain anode and an even (very thin) silver layer was deposited on the inside of the cup.

This was a long time ago and I may have forgotten many of the details, but the one thing I remember clearly, was the need to control the distribution of the plating current by careful positioning of the anodes. It could be that your wire cage is positioned so close to the copper anode bag that it is drawing all the plating current and so shielding the target surface. Could you find a way to reposition the wire cage on the opposite side of the mold?

Just a thought, which may help, As I said, I am no expert but I have seen it done.by one.

Mike

It is the journey that matters, not the destination

Offline crueby

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Re: Electroforming/electrotyping
« Reply #19 on: February 27, 2019, 11:46:49 PM »
If the wire cage is mainly to suspend the mold, could you use insulated wire for it instead, to keep it from attracting the copper?

Offline Admiral_dk

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Re: Electroforming/electrotyping
« Reply #20 on: February 28, 2019, 11:34:55 AM »
Sound to me like you should try to have the wire inside the mould and leave insulated upwards and having the exposed end come out through what will be the middle of the finished surface.  this way the growth will be from the center.

If I had to do it, I would experiment with making a mould first as before. Then make a very small hole around the middle in a place with as few details as possible or even a few places (or more) depending on the surface area size. place the exposed copper wire(s) close to the surface in the hole(s), bend towards the top on the backside and pour another layer of the mould material, so the exposed parts of the wire on the back is encased. Next steps will be as before, with cleaning, carbon, etc.

I hope I make sense and that it will be useful inspiration (to maybe an even better solution).

Best wishes

Per

Offline sorveltaja

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Re: Electroforming/electrotyping
« Reply #21 on: February 28, 2019, 08:00:17 PM »
Mike, that's fascinating story. The wire cage definitely robs a lot of copper. At first, I copied what I saw on Youtube videos, where people used wire cages from start to end of the process.

In fact, I just realized, that the cage is needed only at the very beginning. Then it is simply snipped away, leaving only one wire to contact the molds copper layer. Why didn't I think of that earlier

Cage removed from both sides:


Using of the cage could be altogether omitted, if the graphite layer is sprayed/wetted with copper sulfate first, and then iron powder sprinkled to it. That way the copper layer forms instantaneously.
I have tested it with some iron filings, and it works. So then I ordered iron powder, but it's bit too fine, and floats away with liquid.

Ethanol might be working wetting agent for a fine iron powder. But that needs more testing.

There is still a "thief ring" left around the mold. I did read somewhere, that it should prevent tree-like formations on the outer edges. Not sure about that though.

To optimize the deposition even more, masking should be used. I still haven't found a working solution for that. I have tested using acrylic paint, enamel paint, and a pc-pen, that is used on printed circuit boards.


Somehow copper finds its way through them all, and starts happily to grow a new layer on the top of the masking. Something like rubber paint comes to mind, but they are usually sold in spray cans, which doesn't make it any easier, at least when masking smaller objects.

What comes to anode and cathode, they should ideally be positioned face to face with each other. But as was mentioned, it isn't always possible, because of the shape of the cathode and/or to provide enough space for agitation.

There is an invisible 'diffusion layer' on the surface of the cathode, which should be continuously disrupted by agitation. Otherwise it seriously limits the formation of the deposit, and allows all kinds of defects to form.

It seems to be true, as at the beginning, I was using something similar, to what they use on magnetic stirrers. It creates nice little vortex, but makes way too constant movement of liquid(electrolyte), resulting deep groves, and other streaming patterns on the cathode. When I changed to reciprocal agitation, smoothness of deposition increased noticeably.

But still the concave surface(object in the above pictures) doesn't get enough agitation. I'm planning on building something different, to provide more 'aggressive' agitation, as they say.

Once my ordered 3d printer finally arrives, I should(at least in theory) be able to make something like bank of eductors.     
     


 




Offline crueby

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Re: Electroforming/electrotyping
« Reply #22 on: February 28, 2019, 08:38:22 PM »
Would the same silicon used for the mould work for the masking layer? I am not clear on what is being masked?

Offline Zephyrin

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Re: Electroforming/electrotyping
« Reply #23 on: March 01, 2019, 09:01:04 AM »
This is a fascinating study, thanks to share...
ME 189, 634.  issue 4185. 2003.
looking at the Model Engineer ref cited above, the inlet copper manifolds for a WWI Le Rhone rotary engine were beautifully shaped by electroforming, about 0.04" thick, on cast Wood's metal cathodes melted afterwards. no further detail in the techniques used...simply following a method published before, ME, vol 111, pp104-105; issue 2774; 22/07/1954. I don't have issue that old alas!

Offline sorveltaja

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Re: Electroforming/electrotyping
« Reply #24 on: March 01, 2019, 08:57:32 PM »
Crueby, same silicon might be used for masking - I'll have to test that. What comes to areas to be masked, it works like when you make traces to circuit board, that are to be reserved, while the rest is etched away.

But in this case, the process is inverse, as the areas, where the copper deposition isn't wanted, are masked, leaving only the target surface without mask, to receive deposition.

Zephyrin, thanks. That issue 2774 could be very interesting read. I have also thought of purchasing wood's metal, for that very purpose, that you mentioned.

On the other hand, there is a book called "Electrotyping", which dates back to 1908, that explains processes in quite a simple language.
Although its focus is on the printing stuff, there is a good amount of basics about the subject: https://archive.org/details/electrotypingpra00partiala/page/n4 

Offline ChuckKey

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Re: Electroforming/electrotyping
« Reply #25 on: March 01, 2019, 09:40:42 PM »
Have you tried 'coloidal' graphite such as Aquadag? As I understand it, this would be very much finer than the powder you are using appears to be, which might help with the conductivity of the coating. (It was used on the insides of CRTs.) 

Offline steam guy willy

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Re: Electroforming/electrotyping
« Reply #26 on: March 02, 2019, 01:30:09 AM »
HI, here are the pages from the 1954   Vol 111  article on electroplating.....I do have a lot of the M.E. magazines from Vol 1 No 1 up to the present day.......hope this is helpful

Willy

Offline Zephyrin

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Re: Electroforming/electrotyping
« Reply #27 on: March 02, 2019, 10:12:34 AM »
Thanks Willy, quite useful info in these pages !
 
with all the practical hints given in this thread, I would like to have a go...

Offline sorveltaja

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Re: Electroforming/electrotyping
« Reply #28 on: March 02, 2019, 08:34:47 PM »
Willy, that's wonderfull!. Thanks for providing the pictures. There it says 48 hours for 50 thou(1,27mm) layer thickness, which seems quite good, without agitation(I assume, as it wasn't mentioned).

I have done some tests without agitation, using about 200-300mA for 12 hours, and haven't got even nearly that good results. In the pictures it says potash alum is a part of the electrolyte recipe. Not sure though, what its role is.

ChuckKey, thanks for the tip. I checked Aquadag's availability on the net, and at least in my case, it should be ordered from abroad. Ordinary graphite powder is more widely available, and is also more inexpensive, making it perfect candidate for newcomers like me, when doing numerous experiments.

Zephyrin, sounds good. If you decide to give it a go, let us know.

Lately I haven't done much of electroforming, but instead, hacking together a simple diaphragm pump for agitation, just to see if/how it works.

Offline crueby

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Re: Electroforming/electrotyping
« Reply #29 on: March 02, 2019, 09:08:17 PM »
Do the internals of the pump need to be all plastic to keep it from getting plated?