3D Printing and Electroforming
Defining the Problem:
3D printing is an integral part of the Maker-Space here at GBS, and the world is increasingly relying on it for rapid prototyping. But what if the user needs the part to be conductive, wear resistant, stronger, or just generally need a shiny metal part? They are restricted to using expensive and difficult metalworking techniques, which is out of scope of what most students here at GBS could do.
Concept Generation:
CNC milling, casting, welding, and SLM printing (metal 3D printing) are generally the only ways that metal can be formed to specific design parameters like traditional 3D prints can, yet they are all so expensive and time consuming that they are automatically ruled out for the purposes of student design prototyping.
The only solution that can still give close to the same physical benefits (and sometimes superior aesthetic benefits) is a process called electroplating, or electrodeposition/ electrolysis. Electroplating is when you take any conductive part, dunk it in a solution with a metal salt dissolved into it, and run electricity through an anode to the part (the anode will preferably be made of the same metal as is dissolved in the solution, as it will keep a constant new supply of metal into the solution as it dissolves). This will deposit a thin layer of metal onto the part as electricity flows, and the slower it is done on a smooth surface, the shinier it will be. The only problem with this is that 3D prints aren’t traditionally conductive, so they have to be coated with a conductive paint for the process to be used. The process of plating non-conductive parts is technically called electroforming, hence the project name.
Electroforming can also be quite difficult for the user to do, so some form of semi-automation would be a massive help. Simply something to hold the object in place while it plates would be enough.
Solution Development:
The only thing to consider now is what metal to plate. The main two metals hobbyists use are nickel and copper, both due to their ease, relative safety (A.K.A. they don’t have to be made of cyanide), and commercial availability. Nickel was the initial metal chosen for this project as it provides stellar wear resistance, can be as shiny as silver, and simply seemed to be an appealing option. However we didn’t get very far with this metal as nickel is apparently a carcinogen, so had to move away from it as that is simply far too dangerous/ unnecessary for a school project. This left copper, which while still a very appealing metal it does have its fair share of problems, namely it just isn’t nearly as strong/resistant as nickel, and it will begin to rust after a short time. To fix these problems we decided to combine it with zinc to create brass (while tin as a metal to make bronze seems appealing, it requires a high concentration of hydrochloric acid to create the solution, which is outside of what we want to do for the project). Brass will have the benefit of making it self-lubricating, stronger, rust resistant, as well as antimicrobial, making this perfect for joints & anything people touch regularly (hence why most doorknobs are brass). Not only that, but when brass is made well it will begin taking on a beautiful gold hue, making this also great for aesthetic uses. Making alloys with electroplating isn’t as simple as combining solutions of two metals though, that will just ruin both solutions. Only one metal can be plated at a time, so to make an alloy you simply plate each and then melt them together after. Better yet though, zinc has a tendency to diffuse into the copper structure on its own while plating, so minimal heating is required for a good alloy, which also minimizes any chance of the part deforming.
Creating these solutions is also relatively simple on paper. Simply take a bucket of vinegar, connect two pieces of the metal you want to plate to a power supply, and just run it until the solution turns the correct color (while you can do exact math to figure out how long it will take, there are so many factors that it is almost as inexact as just eyeballing it). Certain additives like salt or sugar can make the solution more conductive and have brighter plating.
As for automation I have a robotic arm that would be perfect for this use, it is programmable and can be connected to the users phone. All that is needed are some simple measurements to have the angles perfect. A mounting plate to both hold the chemicals and arm would be best, as well as barriers to separate the chemicals from the crowd while still being visible. This can be achieved by laser cutting polycarbonate to the perfect size (20×19.5 for the sides, 20×23 for the front), and they can even be engraved to show hazard lines and warnings to dissuade any children from trying to touch the chemicals.
Construction & Testing:
The construction of this project proved to be rather tedious at first, namely due to lack of experience and supplies. Our first attempt at making a solution simply just used two strips of nickel (we were still trying for the nickel solution) connected to a lantern battery in about 1L of vinegar. For obvious reasons this wasn’t perfect, and we only got in about two tests before we disposed of the solution in favor of non-cancerous ones. At this time though we obtained a variable power supply that can put out stable current, which is perfect for electroplating. The first test plating on a metal washer was rather dull, literally, the plating was just a dark metal color. It wasn’t until the second test on the same washer that we got one of the best results of this entire project, the plating was a perfect shiny metal color.
This was due to one of the primary aspects of getting good plating results in electroplating, current density calculations. The current your supply puts out will usually be the deciding factor between a shiny and dull plating, but one current value will not work for all parts. This is due to current density, or current/area on the part, and most solutions have a certain current density that will always give proper, shiny plating.
Nickel plating solutions usually work best at a current density (J) of around 3 I/A, and the surface area of the part is 0.104 m^2. Using the equation
J = I/A, where J is current density, I is current, and A is surface area in meters, we get the equation
3 = I/0.104
We can use this to find the exact current needed for the best possible plating results, and after solving the equation algebraically we get
I = 0.312 Amps
Using this current is what resulted in the test seen above, proving for the duration of this project that proper current density is a very important factor.
After this we officially moved away from nickel plating in general, and began work on the copper and zinc solutions. They were made in largely the same way as the nickel solution, simply taking either copper mesh or zinc strips and dissolving them in vinegar. The copper was the first we made, and it quickly proved to be very different from how the nickel plating behaves. Namely it plates much quicker and at lower voltages, and at least with the copper acetate solution it needed a period to dry for the plating to stick. Using the same current density equation with a current density of 1.5 on a part with a surface area of .2588 m^2, we get this equation
1.5 = I/.2588
When this equation is solved, I = 0.39, which requires much lower voltage compared to nickel, but when tested it did prove to be quite successful.
It took quite a bit of effort to get to this point, namely just with trial and error learning how this new solution behaves.
The next step from here was to turn this from electroplating to electroforming, so we bought some graphite powder and tried mixing it with some paint to see if it would work. It proved to have quite poor conductivity, and the graphite itself tends to escape from the paint, so if it were to be tested in a solution all that would happen is that nothing would plate and graphite would leach into the solution, which while we don’t know exactly what that would do it’s easy to assume it would be very bad. Though while not in keeping with the total DIY aspect this project has had so far, we decided to order a zinc spray paint and later nickel spray paint for the purposes of making the part conductive. We had very high hopes for the zinc spray as it was both cheap and zinc has a very interesting redox reaction with copper, so the copper would theoretically plate electrolessly, without any coaxing from a power supply. This didn’t prove to be the case however, as we stumbled upon what I think may be the most niche and random chemical reaction ever. Apparently, if you try to plate copper onto zinc with an acidic copper solution, the copper will electrolessly plate onto the zinc, but at the same time the solution will begin to dissolve the zinc. For obvious reasons this won’t end up working, trying to plate onto something that is actively dissolving would never end well. All you get in the end is a weird coppery black sludge on top of the part (which is similar to what you get if you don’t clean the part properly). Plating zinc onto copper, however, has more niche chemistry that instead works to our advantage. When zinc is plated on copper, it will plate as normal, but given time (usually a few minutes) the zinc will diffuse itself into the copper and form brass.
After learning that the zinc spray doesn’t work we ordered the nickel spray which has proven to be far superior as far as electroforming goes. From here we began the zinc solutions, which proved to be the simplest of them all. We simply attached some zinc strips to a power supply, added some salt and sugar, and left it for about 15 minutes. This solution has so far proven to be one of the most reliable, doing exactly what you would expect it to without any major problems, unlike the copper solution. Up to this point the copper solution gave us nothing but problem after problem when trying it with electroforming. This is likely due to the fact that the conditions for electroforming are much less perfect than with pure metal, where metals have a resistance of basically zero no matter what you do with paint you will always have a few ohms of resistance.
Due to all of these problems, we decided to just order 1L of a copper sulphate to see if it would work better, and to judge how good our copper solution was. After testing, the copper sulphate proved to be the right choice for electroforming, working very well on the first try. It plated brightly and thickly, without any of the problems the old solution had with the plating not adhering.
You may notice that the plating is uneven in some areas, and that the center barely plated. This is due to one of the biggest annoyances of this project, surface preparation. Electroplating has been described as “80% surface preparation” by many experts who have made careers out of it. If the part has even a little bit of grease on it (which comes from your hand), the part won’t plate. If the part is too rough, the plating will look black and gross. If there are loose particles on the part, they will get into the solution and ruin it. For high quality copper electroplating it takes hours of meticulously sanding and painting parts over and over again with a primer, and then once you’re done with that it takes another few hours cleaning and carefully polishing multiple layers of conductive paint to achieve what are sometimes even mediocre results. What happened with the part above is that while trying to polish the conductive paint we accidently removed too much around that blank area, so it had too high resistance and didn’t plate.
With all of this taken into account we tried to get the best possible test with a 3DBenchy, a common test print for 3D printers.
This test proved to be quite successful, the boat plated evenly with a nice copper color. It isn’t without its flaws, the back left didn’t plate perfectly due to over-sanding, but it is still by far the best test we’ve ever gotten. During MakerFaire we will be doing a live demonstration/test where we will plate it with zinc to make brass.
Solution Evaluation:
We are very proud of what we made, in theory every part of it works perfectly as designed. Every flaw with the plating is more or less due to surface preparation at this point, which may sound simple on paper but it ends up being an incredibly complex part of the project. People have dedicated careers to getting good plating, and at this point we just don’t have the experience or expertise to plate at the level they can. Our only regret with the project is not getting in more tests with the brass, but with how time consuming each test is it wasn’t feasible to do any more before the deadline. We are incredibly proud that beyond a few minor tweaks, our project is perfect as we can make it beyond our own technique.
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