jaeyual@mit.edu
For molding + casting exercise, I wanted to continue the mass study of my last semester’s installation project. The project was based on space-packing of polyhedrons with various size of perforation attracting the public into the corner of review space. The massing layout of module aggregation was not fully developed with lack of time. I thought it would be a nice way to study aggregation patterns with mass production of a module from molding and casting.
[1_MOLD DESIGN]
Since I wanted the object to be rigid, I created a positive mold to cast a flexible mold. I did not make an extra vent holes other than the pouring hole because the object is relatively simple in its geometry and small in its size. The size of the pouring hall was 1/4″ in diameter.
[2_MOLD MILLING]
/material : pink polystyrene foam
/machine : CNC
/location : 4-002
/time : 7 minutes
Because I used 1/4″ round bit for CNC, adjoining bottom surface and perpendicular surfaces have 1/4″ radius fillets. The initial plan was to go through additional profile cuts with a flat bit to create sharp 90 degree cuts, but due to the delayed time schedule, I modified the corners with x-acto knife manually.
[3_GESSO LAYER]
Acrylic Gesso was painted to seal off the surface and prevent casting material from permeating.
[4_MOLD CASTING]
/material : Mold Star 15 (Platinum Silicone Rubber)
/pot life : 50 minutes
/cure time : 4 hours
/ color : green
/ mix ratio : 1A : 1B
Even though I had prepared pink soap as releasing agent, I forgot to apply and ended up breaking the pink foam to get the mold out. I was surprised by the level of details excavated by silicon. If I had more time, I would try using wax for the original mold material to have smoother surface than pink foam.
[5_OBJECT CASTING]
/material : Smooth-Cast 300 (ultra low viscosity liquid plastics)
/pot life : 3 minutes
/cure time : 10 minutes
/color : bright white
/mix ratio : 1A:1B
/location : 7-408 vent room
Two chemicals react very quickly that it gets warm within a minute. Part A is clear white and Part B is clear with yellow tint. The mixture becomes rigid and opaque white within 3 minutes.
I used rubber bands to hold two molds together. The geometry of the object came out clearly, but the surface was a bit too rough that I sanded them. With one package of Smooth-Cast 300, I was able to cast 29 objects. Because I did not know exact volume for a cast, I ended up wasting lot of materials in the beginning. It would be good to calculate the volume of the object first to be efficient. Also, even though its cure time was only ten minutes, it took really long time to cast ( 10 min x 29 = 290 min). If I was to mass-produce same object again, I would make multiple molds, or one big mold holding multiple objects inside.
[FINAL PRODUCT / POSSIBLE AGGREGATION]
COMPLETE FABRICATION 