Molding and Casting

This week's assignment should of been pretty straight forward, but because of small details I had couple of issues to overcome. Yes, issues to overcome and to learn from. The point of the whole FabAcademy. All these issues where some kind of personal errors: lack of imagination, not taking in consideration all the details, not seeing the final result, etc.

The first idea was to design and mold a FabLab keychain (again) using PMC-121 for the mold and urethane for the cast part. I drew the 3D model nicely, generated the correspondent *.png using the fabmodules and started machining the wax. For rough cut I used a 3 mm ball end mill and for the finish cut I have used a 0.8 mm flat end mill. The rough cut haven't finished yet and I was already seeing some issues. Since I have generated the *.stl file only with the 3D model, the end mill didn't had place to pass between the milling limit and my drawing. Therefore it just skipped those parts and the milled model remained connected to the wax limits. This was wrong and the silicone mold couldn't be made as expected. Another issue I was experiencing was the Z depth, when changed the end mill, I have set it up just above the expected height and the finish cut was milling away only a small amount of wax. First attempt was kind of a failure.

I have changed my mind and drew the Deusto logo for casting (first day) and one token (second day) for my final project, a goose game token. This time I haven't forgot to put a bigger box under the design for a correct milling and to be sure that the end mills will pass through between the limits and the models. Both cuts, the rough and the finish, came out quite nicely.

For time constrains reasons (I was traveling back home) I didn't had 16 hours to wait for the PMC-121 to harden and didn't had any urethane at hand at the University to cast models, so I have decided to go with the food suitable silicone rubber. Mixed the parts in 10:1 ratio as much as I could (not quantity, but mixing) and poured in the positive wax mold's. Before this pouring I sprayed some demolding agent over the wax. First day I thought I'll have time for this silicone to harden and have a second go with the PMC-121, but I was wrong and the next day this silicone wasn't harden enough for demolding. At this time I have decided to go with a second mold (goose token), covered the already semi-solid silicone mold and milled out the second design, followed by the mixing and pouring of the food suitable silicone. Since I have mixed enough silicone for all the mold's I made, I have started to pour it in all the mold carefully not to have any bubbles.

At home, and after 24 hour of hardening, I have demolded carefully each mold and they came out nicely, without any unwanted bubbles. This step was followed by a post curing process at 100º C and for 4 hours. After the post cure I have washed the silicone and the fun started (again): melting chocolate for molding. It was kind of a long process, since I had only 2 molds and at every step I had to let the chocolate to cool down, but in the end it was worth it. The molded chocolate came out quite nicely and tasted like haven! Made an extra try with water and the ice also came out quite detailed. Bon appetite and here's some chocolate!