Electroplating / Galvanic deposition of copper on 3D printed PLA objects

TL;DR:

• Current density around $50 \frac{mA}{cm^2}$
  • Lower current means better surface
  • Voltage should be around 1V to 2V in the beginning
• Maximize distance between anode and cathode
• Use graphite paint to cover the object until the surface resistance is around $1 k\Omega$ to $2 k\Omega$ between the remotest location of the object.
• Copper ions travel from positive to negative side
  • Anode is positive and the source (for example a copper pipe or sheet)
  • Cathode is negative and the target (i.e. the workpiece)

• The problem
• Materials used
• The process
• Disposal

The problem

Sometimes you want to 3D print metal objects - but usually homemade 3D printers are currently not capable of printing metal objects like high end laser sintering machines are. On the other hand it’s often not possible to use traditional machining methods when working at home. In case one just wants to get the look and feel of metallic objects one might use filaments that embed metal particles in a plastic matrix - these also exist for wood and stone objects, some for magnetic materials and some are even conductive after the print; these filaments are usually flexible and pretty expensive though. Another way is plating the plastic using a galvanic process.

What is a galvanic process? Electroplating or galvanic deposition is the process of using an electrical current to deposit metal ions by an reduction process onto a target surface. This is usually done in a specific electrolyte. This usually requires a conductive target surface - and one requires different electrolytes for different materials. One should also note that it’s of course not possible to use every metal on every surface - for example it’s not possible to coat Nickel surfaces directly with Gold - one usually uses a Palladium interface layer in this case. Also some materials are hard to coat at home while industry uses cyanide baths - for obvious reasons that’s not a good idea to do at home.

For a more detailed description of the process and it’s limitations there is an excellent paper with the title Improved current efficiency equation for the electrodeposition of copper in the journal of applied electrochemistry.

Personally I started this project because I wanted to plate some 3D printed parts with a conductive surface to be used in vacuum later on, in this blog article I’ll focus on some pure decorative objects though.

Materials used

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• The electrolyte used in the process described in this article is based on sulfuric acid. One is of course able to mix one own’s electrolyte, on the other hand they’re readily available and not really expensive. The professional electrolytes also contain additives for better surface finish.
• A source of copper. I’m using standard copper tube from the local hardware store. One could also use stripped wires, old PCBs, etc. The only important thing is that it’s clean.
  • If you’re using copper pipe it’s a good idea to use a pipe cutter. Not really necessary but saves huge amounts of time.
• A simple current limited laboratory power supply that supports currents up to around 1A is also required for small scale plating projects. It’s good to have some room up to higher currents though.
• Cables that allow easy attachment to the power supply.
• Depending on how you attach your workpiece some kind of copper wire is a good idea. I’m using this to mount some objects (see photos below) on the inside. The PVC insulator withstands the electrolyte so you do not deposit too much material on the wire itself.
• Since PLA is an insulator the first conductive layer has to be added using an electroless process. There are industrial electroless copper processes based on Palladium agents but those are less interesting for home applications. One can simply use graphite, silver or copper conductive sprays. I’m currently using graphite sprays.
• You will require some kind of cleaning agent. I’m using Acetone for this purpose.
• Some pairs of gloves are a good idea since you’re handling some chemicals - though many experienced chemists won’t use gloves with these materials.
• Steel wool is really useful to clean off copper residues, prepair the anodes, etc.
• A glass jar or some other bath that’s either made out of glass or plastic. It’s a good idea to have a closeable jar so one doesn’t have to transfer the electrolyte between the storage and plating receptacle.
• In case the copper coating has only decorative but not functional purpose some kind of passivization lacquer such as Zapon.

The process

Since you’re working with chemistry you should use gloves if you do not feel really comfortable working with sulfuric acid and acetone. Do these works in a well ventilated area. It’s easy to evaporate enough Acetone to get an explosive atmosphere and the vapors from sulfuric acid as well as acetone are not healthy either. If you don’t feel well after accidentally inhaling or coming into contact with this stuff consult medical assistance. And keep in mind that Acetone dissolves gloves really fast.

The electrolyte should be kept in a separate receptacle that you’re using for plating. In the best case this receptacle should be closeable so that you can store electrolyte inside as long as you want to reuse it. It has to be large enough to enclose the anode(s) as well as the workpiece(s).

First clean the object. The cleaner the surface the better the result. Use Acetone for that for example. You should not touch the object with your bare hands especially if you’ve more oily hands. If you don’t leave fingertips on bare glass anyways you don’t have to worry that much.

Apply 4-5 layers of graphite spray on top of the PLA objects. Let the paint dry between the different layers. At the end the surface resistance should be around $1 k\Omega$ to $2 k\Omega$ between the farthest points of the object.

When the object is ready first clean the the anode (that’s the source of copper, not the object) using Acetone and steel wool and put it into the tank. Attach it to the positive terminal of your power supply. Never let your anode or object linger around in the electrolyte while not plating though.

The distance between anode and cathode should be maximized if possible - and the distribution of the anode around the object should be as even as possible - or the object should be turned periodically. It’s also a good idea to have an anode surface at least as large as the target surface though it works also using just some kind of tube as shown on the photographs below.

Attach the object to a conductor. Currently I’m using PVC coated wire - this can be wound into the desired form to push the PLA object into the electrolyte (do not forget that the PLA will tend to swim at least until all air pockets are filled with electrolyte). This cathode will then be attached to the negative terminal of your lab power supply. Check that the connection is really conductive before putting the object into the electrolyte.

Turn the current limiting to zero. Optionally turn up the desired voltage to around one to two volts.

Crank up current slowly. Note that lower current means slow coating speed but also higher surface quality. Too high current leads to uneven deposition as well as burning of the graphite layer. If you see something smoking current is way too high. As a rule of thumb the current density should be around $50 \frac{mA}{cm^2}$. I’ve reached the best results with plating currents of up to $300 mA$ in the beginning and up to $800 mA$ in the end for small objects.

After the coating has been successful disable the power supply and remove the object from the receptacle. Rinse with clean water for a longer period of time. It might also be interesting to let the object dry for a longer period and rinse multiple times since it’s air pockets are still filled with electrolyte after removal. After cleaning one might want to apply passivization lacquer such as Zapon to prevent any further change in color or corrosion.

You might want to polish your workpiece after plating.

Also take out the anode, rinse with clean water and clean with steel wool if you want to use it again at a later moment. Close the receptacle containing the electrolyte or transfer into the storage container.

Disposal

Note that the electrolyte contains copper and thus has to be disposed as hazardous waste. Follow your local regulations and stay responsible. Copper is a toxic substance if released into the environment in larger quantities - with the amount contained in one liter of electrolyte you could already render a few square meters of land unusable for any further farming and it will be washed out by rain. Do not simply pour copper solutions into the environment or into your local wastewater system.

This article is tagged: Tutorial, 3D printing, DIY