During a small project carried out at Royal Academy of Arts in The Hague, I sand cast a small aluminium ring holder using a 3D printed PLA model. This was done to try and experiment sand casting technique but also to link it to digital fabrication technologies such as 3D printing to explore how this two worlds of digital production and manual craft techniques can be combined to produce interesting results. The initial part of the process involved modelling and printing of a small PLA object which was then used to create a mould by pressing it into special sticky greensand. The model was then removed to obtain a negative where melted aluminium was poured in. Here is all the step that I did to make my aluminium ring holder.
Step 1: Modelling
To start making my little ring holder I did a brief research and compared different existing ring holder cones and their sizes and features. After I had a clear idea of the dimensions and the shape that I wanted my cone to have I started modelling it on Rhinoceros. When I was satisfied with the shape I opened it on Slic3r to prepare it for printing. I set the infill density very low as I did not need it to be particularly strong and the shape was pretty easy to print, then I exported the gcode and printed it on a Multiaker 3D printer. I uploaded the gcode and the Rhino model here in case you want to use it to do the same :)
Step 2: 3D Printing
The 3D printed model was not perfectly smooth and the tip was a bit rough so I sanded it a little, but the dimension and general shape was quite what I wanted and was fitting my ring size, so I went on with the sand casting. The printing took less then an hour and the material used was transparent PLA.
Step 3: Filling Up the Frame
For the sand casting, I used greensand and wooden frames that were available in my school's metal workshop. I tried different configurations with my classmates and then decided to use a big one where to place different model to cast together to save space and materials. We then filled it up with sand by adding it in layers and compressing each one manually first and then with hammers to make it very well pressed and to obtain a good negative into the sand. Here you can see all the models which we cast using the same frame.
Step 4: Removing the Models
Removing the 3D printed models turned out to be less easy then we thought because of the very high pressure of the sand and flat shapes of some of the models. We used a 3D pen to add little tips from which to pull up the models, then, very delicately, were were able to take the models off obtaining a good negative. This shapes were all actually quite simple and did not require two different sides because of their symmetrical geometry. For more intricated shapes with non-symmetrical sides, you might want to use two wooden frames by filling up both of them and then impressing the two different sides one by one. If you do that, you might want to use talk power to help the removal.
Step 5: Melting the Aluminium
To do the casting we decided to use aluminium scraps that we found in the metal workshop. We collected them and placed inside a little iron container (which has a higher melting temperature of aluminium). To melt the pieces we used an oven which was available in the workshop which reaches very high temperature (it started melting at around 800 c° because of different types of aluminium we put together). To make the process a little bit faster though we used a blow torch, placing the container on top of a heat resistant brick in the workshop.
Step 6: Casting
After that, we poured the melted aluminium inside the mould. This was very fun. There is a short video attached so you can see how we did it. We gently poured the liquid metal in and then waited for it to cool down. To make it faster I removed my when it was still a bit hot and placed it under cold water. The sand burned a little giving a black mark to the top cone, but it came out pretty easily by rubbing the model under cold water. Also, the metal was not liquid enough (or I poured too much) so it coagulated on the top forming an extra piece at the bottom, which I thought was quite fun and looked like a candle holder.
Step 7: Polishing
After the casting I decided to clean the ring holder by sanding it with sandpaper, cutting the end part off using a saw and polishing it with a polishing machine. Here you can see the comparison between another casting I did, which I didn't polish, and the final one.
Step 8: Final Result
My final sand cast aluminium ring holder :)