Week 6: Casting and Molding
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Tags | CastingMoldingSilicone |
As a Pokémon fan,
This week, I decided to design and make a Pokeball Keychain out of metal.
I designed the positive of my mold in fusion, and then machined it in wax.
![](Week%206%20Casting%20and%20Molding/IMG_0744.jpeg)
I then poured Oomoo into it and got a negative of my final output.
![](Week%206%20Casting%20and%20Molding/E5460758-E1EA-465F-A4CF-FA954E15C73A.jpeg)
I had to wait a couple weeks for Cerrotru to be stocked at REEF but once it was here I turned on a hotpot for 35 minutes to melt the Cerrotru completely and then poured it in my mold carefully after applying a bunch of baby powder in the mold.
![](Week%206%20Casting%20and%20Molding/IMG_1491.jpeg)
Final result -
![](Week%206%20Casting%20and%20Molding/IMG_1494.jpeg)
OLD
Thinking about my final project, one of the first things that comes to mind as a part that’s appropriate for a casting process is the “skin” or grip of the smart racquet handle.
I wanted to be able to measure how strongly, or positions where the player is gripping the handle -basically touch localization and intensity data. I searched around for what sensing technologies would be appropriate for this, and I came across an artificial skin sensor described in a research paper
![](Week%206%20Casting%20and%20Molding/Untitled.png)
The sensor is basically made by casting two layers of silicone with a grid of electrodes sandwiched between. Conveniently enough, the author also sells a open-source hardware kit to decode the signals and interface with arduino/other microcontroller platforms.
![](Week%206%20Casting%20and%20Molding/Untitled%201.png)
Unfortunately, all his products were sold out or discontinued. I think decoding the signal from 10’s of electrodes may be too challenging to tackle but I need to get more feedback to see if this would be possible.
In any case I decided to dig for a few other options and found a force-sensitive resisotr which can detect pressure/intensity (but not the location of pressure points)
![](Week%206%20Casting%20and%20Molding/Untitled%202.png)
Whichever option I pick, the eventual step will be to cast the sensor inside a grippable material. That’s what I’ll be designing this week.
Molding
For designing the mold, I would need to create a cylindrical grip, but one that has been flattened into ribbons/tape that can be wrapped around the handle.
![](Week%206%20Casting%20and%20Molding/Untitled%203.png)
The FSR sensor on Adafruit has a 24inch x 1/4th inch dimension, so I would need to cast a rectangular block of silicone with similar dimensions. I intend to cast it slightly thicker though so the silicone wraps around the edges of the sensor. I am going with a width of 0.375 for that reason.
![](Week%206%20Casting%20and%20Molding/Untitled%204.png)
Although I haven’t gotten the sensor yet, I wanted to practice how this could be cast. I decided to build a rectangular acrylic box in which i could place the sensor and pour silicone to cast it
Face 1 dimension: 24 x 0.375 in
Face 2 Dimension: 1.5 x 0.375 in
to start off, I laser cut the sides of an open rectangle and joined the pieces using masking tape before applying acrylic cement to create sealed joints
![](Week%206%20Casting%20and%20Molding/IMG_0648.jpeg)
Working with such small acrylic pieces was more difficult than I expected and the joints were poorer than expected too.
After gluing I checked if it was a watertight seal by putting some water in the mold. The water dripped out so I reapplied glue in parts.
Casting
For casting, I decided to use EcoFlex 50, since it was a rubbery material. I mixed parts A and B in a 1:1 ratio and used a vacuum degasser to remove air bubbles.
I then poured it into the mould using a standard large cup - again, the scale of the mould was way smaller than the cup I used so it ended up falling outside the mold quite often. I wiped the excess with a rag, and let it set for 4 hours.
![](Week%206%20Casting%20and%20Molding/IMG_0662.jpeg)