DIANA LI
Engineering, Design, Medical Devices & DIY
OFF THE CHAIN
This was my first time learning to mold / cast, so there were a lot of obstacles including design change, resin not forming on the first attempt, and 3D printing defects. The entire process is split into three phases for clarity.
Phase 1: Design
Initially, I wanted to make a Super Mushroom keychain from Super Mario. However, after the first print, it was very low quality due to insufficient support. The second print was complete, but after sanding, the details on the head and eyes were completely lost.
First print
Second print
Consequently, I used an existing coke bottle design with the following features
(CAD top, front and side views shown below):
Volume = 0.684 cubic inches
Dimensions: 0.765 x 0.765 x 2.437 inch
No hollow voids
STL file can be found here
For the parting line, I decided to use its plane of symmetry. The sketch below includes the mold's wall thickness calculations for a successful part.
Phase 2: Master Fabrication
Below are the top, front, and side views of the digital rendering.
The print with the FlashForge 3D printer was overall successful except the bottom layer contained colored filament and was extremely uneven. Super glue was used to even out the bottom surface, and white paint was used to cover the discoloration on the master.
FlashForge 3D printer
Before sanding
Bottom 3D printed defect
After sanding
After sanding
Fixed bottom defect
Phase 3: Mold and Cast
When making the first silicone mold part, clay was formed up to the parting line, and wall thicknesses from the sketch in phase 1 were used. Clay molding tools were used, and small registration marks were made around the part.
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Before resin was poured in, the following cut was made at where the bottom of the coke bottle would be. This placement was chosen because the bottom is where the part sits, and the aesthetic is not extremely important.
2 part mold and hold for resin
Scaling for resin
Unfortunately, the first attempt of casting failed since the resin used had been sitting past the recommended time of 20 minutes after mixing.
Two final attempts were made.
Second attempt rough cast
Second attempt rough cast
Third attempt final cast
Third attempt final cast
Final Product and Design Improvements
Overall, there were a lot of unexpected difficulties in this project, and there are a couple of things I would improve.
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Pour silicon slower. The first part had small air bubbles on the edges of the coke bottle, and this may have been caused by pouring in the silicon too fast initially.
Use acrylic paint. I painted with white spray paint, resulting in some rough areas. I sanded it only a little, since I was afraid the paint would chip.
Use larger registration marks and thicker wall. This would've ensured for a more precise contact between the mold parts and may have resulted in a better product.
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In conclusion, a lot of changes could be changed for next time. However, this project was extremely enjoyable for me because I've never been exposed to molding and casting my own parts and these are skills I would like to use in the future.
Close-up before paint
Final product before painting
After painting
3D printed part, rough cast, final cast from left to right