Electroforming - thin walled copper parts from 3D prints

[lee webster]

Thanks for taking the time to post this. I hope one day I can use the information.
If you removed the pla by heating the new copper part with a blowtorch, then the copper part must be quite strong.

 

[Oldiron]

Would placing multiple copper anodes, electrically connected together, around the perimeter reduce the line of sight plating problem and result in a more even plating thickness all around? Something similar helps when electrolytically removing rust. Note, the amperage required may increase in relation to the area of the anodes. Bob

 

[Lloyd-ss]

Peter, brilliant work, and thank you for sharing it.
Your experiences seem to be spot-on and you have solved many problems. Years ago I worked in a facility that plated conductive slip-rings onto plastic mandrels using the conductive paint method like you. Copper was always used as the base coat because it had excellent "throwing power" and would successfully plate over irregular surfaces. The electrical hot spots of sharp corners and un-plated holes were dealt with by designing them out of the part as best as could be done. Sometimes troublesome parts were removed from the bath and the sharp copper points carefully files off, and then put back into the bath. But it was risky because the plating process did not like to be interrupted.
Once the copper was plated to the mandrel or part, it provided a perfect plating base for a thin plate of nickel or silver or gold. Often, a thin flash plate of copper was used between the different final layers. The original copper plate was smoothed before the final plating was applied. You can always see the thin copper plate underneath the top chrome plate of many kitchen tools, etc, as the chrome wears away.

I am wondering how malleable the copper parts are, and if they respond well to the normal copper annealing process to take care of any work-hardening as the parts are finessed into a perfect fit?
Again, brilliant!

 

[Peter Twissell]

Bob,
I did attempt to do as you describe with a shaped anode, to broadly follow the shape of the part. This actually made the situation worse, because the distances to the closest parts of the anode were so much smaller than the distances to the furthest parts.
The electric field density at the cathode is proportional to the inverse square of the distance to the anode, so parts which are twice as far away will have only 1/4 of the field density and therefore will plate at 1/4 of the rate.
If the anode is 6" away from a 2" wide part, then the furthest point of the part is 8" away (or 1.33 x 6). Thus the field density at the furthest point will be 1/(1.33 x 1.33) = 0.56 of the field density at the closest point.

 

[Peter Twissell]

Lee and Lloyd,
the finished parts behave exactly like any other copper. When I heated the part to melt out the plastic, I got some parts of it to red heat and quenched in water. As expected, this annealed the copper.

 

[Bentwings]

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?

You can get cero bend from mc master Carr it allows easy bending of thin wall tubing just pour it in cool it below room temp and bend away then warm it in boiling water pour it back into a plastic container I’ve used it for a long time . I have a new ingot of it ordered now.

Byron

 

[Peter Twissell]

I could have made the exhaust pipes with 1.5D bends by bending copper pipe, but the induction manifold has 1D bends and a relatively complex join with two curved sections meeting.
I chose to electroform the exhaust pipes as a trial run before attempting the induction manifold.

 

[Peter Twissell]

Another couple of points worth mentioning...
The warm electrolyte and the larger water bath will both evaporate at a significant rate.
I found it necessary to top up the electrolyte with distilled water and the larger bath with tap water every day.
If you want to interrupt the plating process, either to measure the part, to clean up any bobbles which may start to form, or perhaps just because you'll be away for a few days, the part should be removed from the electrolyte and washed in distilled water to remove electrolyte and prevent oxidation of the surface which will impair subsequent plating.

 

[Peter Twissell]

When plating, the formation of bobbles indicates that the current is too high.
It is possible to file bobbles back to a smooth surface, but if they develop early in the process, there may not be enough thickness of plating to support itself against filing forces. In such cases, it is best to peel off the plating and start again at lower current.

 

[Steamchick]

Thanks Peter. Your explanations show a very good understanding of how to manage this difficult task. I thought your were "attempting the impossible", but that just shows where persistence and study combine to create things we lesser mortals may avoid.
Well done sir!
K2