14. Molding and Casting

This 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

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.

Machine Setup and File Loading

1. I placed my material on the sacrificial bed and secured the board properly. (I used foam)
2. I deactivated the emergency button and pressed the green button to let the machine return to the origin.
3. 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.
4. To load the file, I inserted the USB, clicked the "Files" button, selected the USB, chose the file, and pressed "Play".

I used Smooth-Sil 950 silicone and Part B950 to make the mold, following the instructions on the datasheet: Smooth-Sil 950.

1. 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.
2. First, I poured water into the mold space, marked the volume, and then added the same volume of Part A.
3. 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.

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). To 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.

Files

• Mold

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.