Week 7: Molding & Casting

This week our assignment was to design a 3D mold, machine it, and cast parts from it. I envisioned creating a clear resin ring with a large carpenter bumblebee nestled inside of my design. I built upon a 3D printed ring I had previously made in Tinkercad.

 

 

 

 

 I then 3D printed my ring using our lab’s Taz printer with blue PLA.  Using the ring, I was able to make a silicon rubber mold. The Oomoo brand was easy to use, and quick to cure! This mold was very flexible. I also 3D printed two molds. My experiment with the 3D molds produced a bouncy silicone rubber ring, that wasn’t perfectly lined up! Then I poured a liquid plastic, Smooth-On, into my 3D printed mold, without anything to prevent the two plastics from fusing together. The liquid plastic set & hardened very quickly, within 10 minutes. The container we poured it from was noticeably hot, also! I decided to go back to Oomoo with my ring sliced, and 3D printed in halves(NETFAB STL file) I used epoxy resin this time and experimentally stuck a bee into the Oomoo mold. This did not produce a very nice effect once the ring cured a day later. The layers in the plastic diffused the outer part of the ring, the open air side cured smooth and crystal clear! I will have to sand my 3D printed ring and start over, this time lining up pegs so the two halves will be as seamless as possible!     

Our fab lab group was fortunate enough to have a friend teach us sand casting at his forge. In preparation I lasered some 1/8” birch wood arrows. My plan was to create metal arrows I would be able to hang up and make a wind chime. I learned many things about sand casting. For one, the sand mixture for the molds contains not just sand, but clay & motor oil too. You must be very precise making the hole and bridge that the liquid metal is poured into. The aluminum takes about an hour to heat up to pouring temperatures. Once the metal has been poured into the molds, fifteen minutes later you can break it open, carefully pick up the cast, and cool it off in water. Then, you have to break the bridge of metal between your two shapes, and grind off any imperfections. My thin, delicate arrows turned out much better than expected!            

Here is a link to a video of breaking the molds open!