Electroforming - thin walled copper parts from 3D prints

[Peter Twissell]

Following my first foray into electroforming, I shall attempt to collect my experiences here in order that anyone with an interest can assess whether the process is suitable for their part.

I find it useful to begin with a summary of the process and applications:

Electroforming material, for our home workshops, is practically limited to copper.

Parts may be created with any desired wall thickness, but thicker walls means more plating build and all the issues which come with it are amplified. 1mm is a practical thickness in my limited experience.

Wall thickness is likely to be uneven to some degree, depending on the shape of the part. A broadly semi-circular section oil sump, for example, would be expected to plate with reasonably consistent wall thickness, while a complex shape or one with small internal and external radii will build up more at the external radii and less at the internal radii.

Equipment and consumables are not expensive and are readily available (in the UK at least). The most expensive item will be the power supply, which should at least have a current reading and ideally have a current control (as opposed to just a voltage control). Copper sulphate, sulphuric acid, distilled water, metallic copper (e.g. domestic plumbing pipe), graphite paint, a fish tank heater and some plastic tubs will complete the set.

 

[Peter Twissell]

The kit:

Power supply - at the lowest cost end of the scale, it would be possible to plate using a 1.5V battery. For more control, I would recommend a supply with current control or at least a current reading. The actual power requirement is small, in the order of 1 watt for the parts I have made.

Bath - I used a 1 litre ice cream tub, but any plastic, ceramic or glass container can be pressed into service. Metal containers are not suitable. Metals may contaminate the electrolyte and cause short circuits.

Heating - the process will not work at temperatures below approx. 25°C. The copper sulphate will crystallise out at lower temperatures. I used a fish tank heater of 50W set to 35°C. I was dubious as to whether the electrolyte would affect the heater, so I placed the plating bath in a larger bath (cat litter tray) and heated the water in the larger bath.

Copper Sulphate - sold as copper sulphate pentahydride (blue crystals) and generally available on ebay etc.

Distilled or de-ionised water - generally available from hardware and motor parts retailers.

Sulphuric acid - available diluted to 37% as battery acid. Supposedly restricted in the UK, but still appears to be generally available from numerous online sources.

Copper anode - this needs to be a fairly high purity copper. Domestic plumbing pipe is adequate, but does leave some black residue in the bath.

Graphite paint - readily available from ebay etc.

 

[Peter Twissell]

The part:

While it should be possible to form any part by this process, there are certainly some features which will make life more difficult.
Plating will build up faster (and therefore become thicker) at external corners. Similarly, plating will build more slowly and end up thinner at internal corners and radii.
If your part looks like a starfish, expect thickest plating at the ends of the arms and thinnest plating in the 'armpits'.
If yor part looks like a pudding bowl, plating thickness should be more even.
None of us are making starfish or pudding bowls, so each of our parts will be somewhere between the two.

The size of the part will determine the size of bath required. A part which occupies nearly half the bath will have some surfaces twice as far from the anode as others, so plating will build faster on the nearer surfaces. Either use a larger bath, or a non-conductive baffle (details in a later section).

The former for the part is in effect the space inside it. This may be a 3D print, carved in wood, cast in white metal or whatever the builder finds convenient and can be removed later by heating or chemical dissolusion. If the former material is non-conductive, it will need to be painted with graphite paint over areas to be plated. Areas not to be plated can be 'masked' with any non water soluble paint.
Water soluble materials such as 3D printed PVA may appear attractive as they can be washed out when the part is finished, but they also require extra care to ensure that they are completely waterproofed with paint before they are immersed in the plating bath.
The builder should consider how the part will be suspended and connected in the bath. Note that light materials such as 3D prints will initially be less dense than the electrolyte, so they will need to be held down until enough weight of plating has built up.
A simple mount can be created by gluing a heavy copper wire (e.g. from domestic twin and earth cable) to an area which is not to be plated, then painting a thick line of graphite from the area to be plated to the copper.

 

[darwenguy]

This sounds realy interesting, very clever. It would be nice to see the results. Im just trying to think of somthing i could use this for now.

 

[Peter Twissell]

This is the intake manifold I made for my 15cc sidevalve twin.
The pattern was 3D printed in PLA.

 

[Peter Twissell]

The former, made from a 3D print, wood, white metal or whatever you choose, needs to be made to allow for the thickness of copper to be deposited.
the surface of the finished part which faces the former will confirm to it precisely, while the other surface will likely be somewhat uneven.

For some parts, such as a sump, it may be preferable to make a female former, so the exterior surface of three finished part is smooth.
Note that electroplating will not work well inside holes, tubes etc. Hence a part such as the manifold shown earlier can only practically be made on a male former.
The conductor which will provide the electrical connection to the former should be located so that it can be conveniently cut away from the finished part.
There is no reason not to use multiple supports / conductors on the part, as required.
If the former is made from wood or other non waterproof material, it must be lacquered or painted all over.
Conductive graphite paint should be applied generously to all areas which require plating.
It is important to make sure that there is a good electrical path from the graphite painted surface to the conductor. This is most easily achieved with a thick line of graphite paint.

 

[Peter Twissell]

The bath needs to be large enough to allow the anode and the party to be well separated.
Using the manifold above as an example, it occupies around half of my small 1 litre bath. At this size, I had a significant problem with plating building rapidly on the surfaces close to the anode, leading to formation of "bobbles".
Ideally, the bath should have been at least twice as long, i.e. four times the width of the part.
In the event that it is not practical to use a large bath, this issue can be mitigated by placing non conductive baffles in the bath, so that electric current is forced to travel around the baffles.

You will need some means to support both the part and the anode in the bath.
This may be as simple as some bent copper wires, hooked over the sides of the bath.
Don't forget that a light former will float and may need some weight or fixing to hold it immersed in the electrolyte.

 

[Peter Twissell]

Heating the bath is necessary to maintain the temperature required for plating, unless you live somewhere particularly warm.
I used a fish tank heater in a large bath of water, with the plating bath stood in it.
I have been told that it is fine to put the heater directly into the electrolyte, but my heater would have taken up too much space in the plating bath and I was not confident that it would not have suffered ill effects from the acidic solution.

 

[Peter Twissell]

The electrolyte is mixed in the following proportions:
200g copper sulphate pentahydrate crystals
130ml dilute sulphuric acid (battery acid)
Distilled or de-ionised water to make up to 1 litre.
150mg (a small pinch) of common salt

A plastic container, such as a (clean!) milk bottle, with a sealing cap, is ideal for mixing and storing the electrolyte.

Heating the distilled water will make it much easier to dissolve the crystals.

Start by putting around half a litre of hot distilled water into the container, then add the copper sulphate crystals and mix until dissolved.

Add the acid to the solution. Never start with the acid! Adding water to acid can be disastrous.

Top up to 1 litre with distilled water and add the salt.

The solution may be stored, but if it gets cold the copper sulphate will crystallise out.
If this happens, decant the solution into another bottle to separate the crystals, which can be broken up with a mortar and pestle. Warm the solution, e.g. by standing the bottle in hot water and the crystals will dissolve easily.

 

[Peter Twissell]

For the anode, any clean copper of relatively high purity will do.
Domestic plumbing pipe is ideal, but don't be tempted to use anything which has solder, limescale or other deposits on it. Contamination will quickly soil the electrolyte and plating.
The anode should be of at least the same surface area as the former and at least double the weight of plating to be added to the part.

 

[Peter Twissell]

With your heated bath, power supply, electrical wires with crocodile clips, former, supports and electrolyte all ready, it's time to set up and start plating.

The electrolyte is slightly acidic, but not dangerously so. It's a good idea to wash your hands if you've touched it and certainly don't drink it!

I found it convenient to set up the former and anode in the bath before adding the electrolyte.

If you are using a larger water bath for heating, get the water up to temperature before you put the electrolyte into the plating bath.

The former must be suspended so that it will be totally immersed in the electrolyte and not touching the plating bath sides or bottom.

The anode is less critical, it can lay on the bottom of the bath and/or be propped or clipped to the side.

Connect the power supply negative to the former and positive to the anode.

Add the electrolyte to the plating bath.

Set the current starting at around 0.2 amps per square inch of former surface area.
If you have designed the former in CAD, it should be possible to read the surface area from the CAD software, otherwise, a rough calculation or estimate will do. It's only a starting point, so doesn't need to be accurate.

In the first few minutes, you should see plating start to cover the former. It will appear blue green, for to the colour of the electrolyte.

For the first few hours, make regular checks on progress.
If you see any bobbles beginning to form on the surface, reduce the current.
If the bobbles are only on the surfaces closest to the anode, it may be worth turning the former around at this point.

At any time during plating, the party may be lifted out of the solution for inspection. Measurements taken at several locations will show the thickness and consistency of plating.
Turning the part at regular intervals will help to achieve an even thickness.

 

[Peter Twissell]

The part will come out of the bath a soft pink colour.
The part can be cleaned up as required with files, Emery paper, Scotchbrite etc. just as one would with any other copper part.

 

[Peter Twissell]

If the part is to be brazed or soldered, it will be necessary to remove all trace of graphite paint from the relevant surfaces. Graphite is very effective at shielding copper from even the more aggressive acid fluxes.
The photo shows the intake and exhaust manifold assembly for one of my engines, made from 3 electroformed parts and two pieces cut from copper sheet.

 

[awake]

Peter, does it have to be sulfuric acid in particular, or will other acids work? I ask because my only electroplating experience thus far has been with nickel plating; for that I used vinegar as the electrolyte. It worked very well ... but maybe that would not be true for copper?

 

[Peter Twissell]

I don't know whether other acids would work, I've just followed instructions from a few jewelry making websites.
I might guess there could be a relationship between sulphuric acid and copper sulphate, both containing sulphur.

There is considerable scope for refinement of the plating process and I've no doubt some will pursue perfection.
For my purpose, a functional set of parts was enough.

 

[awake]

I don't know whether other acids would work, I've just followed instructions from a few jewelry making websites.
I might guess there could be a relationship between sulphuric acid and copper sulphate, both containing sulphur.

There is considerable scope for refinement of the plating process and I've no doubt some will pursue perfection.
For my purpose, a functional set of parts was enough.

I hear that - "If it ain't broke, don't fix it"!

 

[stanstocker]

Thank you for the time and effort to put up all of this information!

Cheers,
Stan

 

[Gedeon Spilett]

Very informative and useful thread, thanks to share your hints and experiments !
I certainly will have a go, I feel it just like an obligation to try...

 

[Shopgeezer]

Great description. I have read about making complex exhaust stacks out of foam tubes and removing the foam after plating by dissolving it in acetone. If you printed these formers how did you remove the PLA?

 

[Peter Twissell]

The PLA was removed by heating with a blowtorch.
Most of it melted and dropped out, the last few bits burned.