For the molding & casting assignment, at first I wanted to create a small model to generate a continuous surface, taking as a point of departure the work on the subject made by Dr. Erwin Hauer. The original module had a somewhat complex mold partition curved surface, that after some evaluation, I concluded it will result in the impossibility of removing the round radius between part and mold using a flat end mill. Anyway, I´m showing part of the work on that model before changing to the definitive one.
After that I changed to a more simple geometry that can be made in a two part mold, but still with the original objective of creating a modular design that could assemble a larger object by aggregation of them. I´ve designed an hexagonal based slanted geometry with a hole in the middle. On its six edges it has an small undercut which serves as a drill guide in order to join the modules using simple cable zip ties.
Open and closed mold cross section:
I´ve made some toolpath tests using FabModules but it took forever to calculate them. At least it was able to read my STL file correctly.
After that, I´ve continued working on the Modela software, making some virtual milling runs to check for toolpaths and interferences.
Those toolpaths were used for milling blue modeling wax. I´ve considered Renshape at first but after having seen the smooth finish of wax I opted for it.
As for the mold material I wanted to try OOMOO 30 solicone rubber from Smooth-On industries, since it´s a simple material to use, without the need of catalizer and degassing. The resulting mold matched perfectly the wax positive without bubbles. The only downside of this silicon rubber is it has longer curing times than other more conventional white RTV rubbers (6 hours of curing plus another 4hours of postcuring in an oven at 65° C.)
For casting I´ve chosen to use Model-Pro urethatne based resins for modelmakers. These are easy to mix in a 50/50 proportion and contain no phthallates or VOC free (Volatile Organic Compunds.) I prefer urethane based intead of polyesther resins, for they have much less shrinking and bubbling an less curing and hardening time. Either for silicon rubber and resing casting I´ve used Smooth-On mold release.
I’ve paid with a bubble, the omission of making some little vent channels… (but just one bubble, not bad for such a mistake..)
I´ve managed to quick add a couple of vent channels. More parts coming soon.
The files for this assignment can be found here: