Molding and Casting
This week: design a 3D mold, machine it, and cast parts from it.
I decide to design and cast a coin with Fablab and Fablab Taipei logos on it. The procedure is as follow: draw the coin in Rhino, CNC the positive mold onto machinable wax, cast the negative with the wax positive, and use the negative mold to cast out the final coin.
Instead of casting the coin out of resins, I would like to try a low melting metal pewter alloy called "Cerrotru" (Tin (Sn) 42%, Bismuth (Bi) 58%), which has a melting temperature of 281°F/138°C. To be able to cast pewter, I will use "Smooth-Sil 950", with Useful Temperature Range from -53°C to 232°C, to make my mold.
Update 4/26: I learned from the awesome people in Wellington that, If you apply dish washing liquid to the plaster mold and let it dries out before pouring the metal, it will become much easier to remove the plaster after the metal cures. I definitely will give that a try when I get the chance!
Here is another method of producing really quick but detailed 2.5D mold for molding with Cerrotru.
On the left are the new batch of coins I cast with a new bubble free mold, which turns out nearly perfect.
On the right is my first attempt to cast on a laser engraved MDF. It turns out the metal was too hot when I pour. This generated a lot of bubbles that disturb the cooling and give the face a ancient rustic look.
Here is the result of the workshop I host within Fan2. One laser cutted 6mm MDF acts as boundry, and one engraveds 3mm MDF provides the face mold of the coin.
Two pieces mdf clamped together to provede a mold for a one sided coin.
Freshly opened mold.
It turns out, if I pour the metal right after it melts, the temperature won't burn MDF at all, and the result cast have a nive texture with very fine detail. All done without talc powder of dish wasing soap!
In fact, OOMOO 30 holds up to the temperature really well! Now I can just use OOMOO for soft mold instead of having to use smooth sill and doing all the degassing.
OOMOO 25 holds equally well compare to OOMOO 30 and smooth sil. Although a bit soft compare to the others, I still managed to get more than 7 casts out of a single mold before the mold shows any sign of tear. Still, not demage due to the heat, awesome!