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!