14. Molding and Casting
Group Task:
Group taskThis week, I decided to make a flexible silicone case for my final project using a foam mold and piece of sanded filament.
I chose this material because it could be a good option to integrate into clothing.
To start, I thought about designing the piece like a eggshell..
I needed to create three molds:
- Mold 1: Inside of the case
- Mold 2 and 3: Outside of the case
First, I started by measuring my PCB.

Then, I decided to create the middle part.




Then, I made the exterior parts.
These parts are for the mold of my mold(negative).


Then I decided to make a new mold, because I needed a deeper one. I realized that the best idea for my case was to create a positive mold.
To make this mold, I used the same method that I used to assemble my piece, but this time I used the combine tool to change from negative to positive.

Mold assembled




Using Vcarve
First, I chose the dimensions of my material and i imported the file in STL:
- Y: 145 mm
- X: 85 mm
- Z: 38 mm
Then, I used two techniques:
- Roughing: To remove most of the material
- Finishing: To achieve a clean and smooth result
For each technique, I used two tools:
End Mill 1/4
- Type: Universal end mill
- Cutting diameter (D): 0.25 in (6.35 mm)
- Flutes: 2
- Cutting depth: 0.125 in (3.175 mm)
- Stepover: 0.1 in (40%)
- Spindle speed: 18,000 rpm
- Feed rate: 3,000 mm/min
- Plunge rate: 800 mm/min
- Chip load: 0.0833 mm
Cut Spiral Ball Nose 3/32"
- Cutting diameter (D): 3/16" (4.76 mm)
- Tip radius (R): 3/32" (2.38 mm)
- Cutting height (CH): 1/2" (12.7 mm)
- Shank diameter (SHK): 1/4" (6.35 mm)
- Total length (OAL): 2-1/2" (63.5 mm)
- Flutes: 2
- Cut type: Up-Cut Spiral
- Feed Rate: 1,905 – 2,540 mm/min
- Chip Load: 0.076 – 0.102 mm
- Plunge Rate: 572 – 1,270 mm/min (30–50% of feed rate)
Tool information: Amana Tool Product Page
With this information, I was able to configure the tools correctly.






Using the machine(Asia Robotica)
Machine Setup and File Loading
- I placed my material on the sacrificial bed and secured the board properly. (I used foam)
- I deactivated the emergency button and pressed the green button to let the machine return to the origin.
- I set the starting point to 0 for the X and Y axes first, and then did the same for the Z axis. I adjusted the Z origin by carefully lowering the tool until the drill bit just started to scratch the material.
- To load the file, I inserted the USB, clicked the "Files" button, selected the USB, chose the file, and pressed "Play".








Casting
I used Smooth-Sil 950 silicone and Part B950 to make the mold, following the instructions on the datasheet: Smooth-Sil 950.
- I added 100% of Part A and 10% of Part B by weight. To calculate the correct volumes, I used water to measure the cavity.
- First, I poured water into the mold space, marked the volume, and then added the same volume of Part A.
- To calculate the amount of Part B, I divided the weight of Part A by 10 and then multiplied it by the density of Part B, which in this case was 1.24 g/cc.
- Part A: 84.6 g
- Part B: 8.4 g (adjusted: 6.77 g)








Fails
💥 Resin Printer Issue
I wanted to print with the resin printer, but the bed detached from the base. I fixed it and i done other mold with that(I'll upload it soon with the right settings). o make my centerpiece, I used resin filament instead, but I have to sand it.
⚠️ Tool Breakage
I broke the tool because the distance in my mold was too small. The finishing tool started cutting before the roughing tool had removed enough material.
🧪 Incorrect Mixing
I made a mistake while mixing the silicone. I accidentally mixed Part A of Smooth-Sil 950 with Part B of a different silicone (Silicone 3030). I realized the mistake when the mix didn’t cure properly, so I had to redo it with the correct components.
Review of Initial Results
Clearly, these are not good results, likely due to the mold design. Maybe I need to redesign the mold in a different way. For now, I’ve decided to make a new mold.


Mold printed in resin
Design
- Sketched half of a cow's face.
- Used the Mirror tool to create a symmetrical face.
- Extruded the cow shape to make it 3D.
- Created a rectangle around the cow and extruded it upward to form a box mold.


Preparing the Model in Chitubox
- Opened Chitubox and loaded the STL file.
- Centered the model on the build plate.
- Ensured the flat side was touching the platform.
- Added and adjusted supports.
- Clicked Slice and saved the file to a USB stick.







Printing the Mold (Elegoo Saturn 2)
- Turned on the printer and inserted the USB.
- Selected the file on the touchscreen and started the print.
- Checked that the resin vat had enough resin.
- Removed the print using a metal scraper.


Washing and Curing the Print (Mercury Plus 2.0)
- Filled the container with 90%+ isopropyl alcohol.
- Closed the lid and washed the part for 8 minutes.
- Air-dried the part.
- Replaced the container with the turntable.
- Placed the dry part and cured it with UV light for 8 minutes.


Casting

- Used Smooth-On 3030: 100% Part A and 10% Part B.
- Measured volume with water and marked the level.
- To calculate the amount of Part B, I divided the weight of Part A by 10 and then multiplied it by the density of Part B, which in this case was 1.30 g/cc.
- Part A: 180 g
- Part B: 18 g (adjusted: 13.84 g)



To create the shape, I used polyvinyl alcohol (PVA) beads and poured them into the mold with water until they hardened after 8 hours.




Final Result
The final mold captured the cow shape successfully.

Files
Conclusion
Making this case with a mold is not easy. Despite the complications, I am learning the importance of checking my measurements carefully to get a good result.