One of the most common complaints about 3d printed parts is with regard to their surface characteristics. Most are made from some type of plastic, and parts printed in other materials are expensive and rarely live up to the expectations people have of objects of the same material made using more traditional processes.
I've been interested in metalization processes for 3d prints as they improve the structural quality as well as the appearance of printed parts. Parts that would serve only as appearance models can, in some cases, be used as functional prototypes following plating. In addition, while the metal plating doesn't completely hide the fact that the part has been 3d printed (as we'll see in this Instructable), it has the ability to change the perception of the piece entirely.
Finally, metalization opens doors to future finishing possibilities, including patination, whether natural or accelerated. While I didn't have time during my residency at Pier 9 to fully explore this potential, I hope to do so in the near future and will be sure post an Instructable about it when I do!
Step 1: Creating the Model
For this piece, I was interested in pushing the limits of thinness given the added strength from metal plating and the complexity possible with the Objet prints.
Once I had modeled the stranded structure forming the exterior of the shade, I inserted a small fixture that would interface with a standard porcelain socket. I've included a digital model of that fixture here.
Step 2: Prototypes & Material Samples
After researching the topic, I came to understand that although metal plating 3d printed parts is reliable and rapidly becoming more commonplace, Objet (PolyJet) 3d prints present a particular challenge to the process. Speaking with service providers, they indicated that the residual, water-soluble support material interferes with the plating process, producing parts with varying levels of surface quality, adversely affecting the bond between the layer of metal and the part, and potentially causing the plating to degrade faster. Several providers declined to plate the parts at all, and most others warned that the surface quality might not meet my expectations.
You can see some of the less-successful plating options in the last two images. The metal finishes on some of these parts would rub off with light contact and the stark contrasts between glossy and matte portions of the models proved unacceptable. In fairness, the aluminum actually plated fairly well, though I believe that is due to a slightly different application process. Moreover, I was more interested in the warm tone provided by the copper for reflected light.
During my research, I ran across this white paper from Objet. I reached out to Morganic Metal Solutions Ltd. who were mentioned in the paper as a service bureau capable of producing the desired results. After some initial conversations, I sent them a small sample of the final part that I had in mind. I was very impressed by the quality of the sample part I received from them, and moved forward with the preparations for the final piece.
Step 3: Printing
The Objet printers are capable of printing a variety of material types - the Vero and Tango series of materials are probably the best known and most commonly used, but other materials exist as well - ABS-like, Polypropylene-like, Hi-Temp, etc. I chose to print my part using the Polypropylene-like material (Endur) for two primary reasons. First, the material is a strong, but forgiving plastic material. These properties gave me the best chance for removing the support material around very delicate regions without damaging the part. Second, unlike the ABS-like material, Endur requires only a single resin cartridge, allowing the print to be run in 'High Speed' mode. This reduced the print time of my model from 54 hours to 27 hours. Reducing the active print time almost always increases the likelihood of a successful print result.
Step 4: Post-Processing
For all complex parts printed via a PolyJet process, removing support material will likely be a challenge. It's important to develop a strategy for removal of all the support material from a part without damaging the final piece. There are three primary means of support material removal, each with their own specific strengths: manual removal, water wash station, and lye bath.
I recommend first manually removing as much support material as possible. While this may be time-consuming, it allows immediate tactile feedback in the process and the most precise control over how the support material is removed. I was able to work my way around the part slowly, ensuring that there were no imbalances that put stress on the part. Once I had removed all the material I could access by hand, I soaked the part in water for about 20 minutes to soften the support material. When dealing with fragile, delicate parts, it's important to soak the part only after the bulk of the support material has been removed. As the support material soaks, it tends to expand. If a fragile part is still completely encased, it can break under this stress.
After soaking, I placed the part in the wash station and used the spray nozzle to access the crevices and other parts of the model that were otherwise inaccessible. As a final step, I placed the nearly-clean model in a diluted lye solution in a circulator and allowed the part to soak for approximately 30 minutes. After rinsing thoroughly and drying, the part was finally ready to be sent out for plating.
Interestingly, after I had sent the final parts to be plated, I received an unusual suggestion from Morganic about support removal for PolyJet parts. A printing service bureau that they work closely with recommends two additional steps at the end - a soak in 40 degree Celsius olive oil followed by a soap & water bath to remove the oil. I haven't been able to try the process myself, but would be interested to hear anyone's experience in the comments.
In retrospect, while the print didn't use an unusually high amount of model material, I would like to have reduced the amount of necessary support material. I would probably re-configure the model to be printed upright on the bed so as to avoid supporting the entire interior of the shade.
Step 5: Plating
After removal of all support material, I sent the part to be plated. Having tested a smaller portion of the actual piece in the real material at the prototype stage, I could be fairly certain of the results of the process. Still, packaging of such a delicate object, particularly in its un-plated state, proved to be a challenge. Were I to do it over again, I would have used a double-crated solution with foam bead fill.
As a side note, if you are interested in metal plating 3d prints, it's best to maintain realistic expectations. The plating process will not erase or smooth out the build lines left by the printing process. In fact, if the metal may make them more visible due to the reflectivity of the surface. This was not so much an issue with the print here due to the high resolution of the Objet printers, but good to keep in mind for FDM or other low-resolution technologies. These are best treated before plating by sanding to a smooth finish. Make magazine published a good article outlining some general guidelines for this.
Finally, as copper will patina, I am currently looking into methods for sealing the part - clear coat or similar. I'm still weighing various options, but will update this Instructable with whatever solutions I find.