14. Molding and Casting

Group Task:

Group task

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 used 100% of Part A and 10% of Part B by weight, following the recommended mixing ratio provided by the silicone manufacturer. This means that for every 100 grams of Part A, I needed 10 grams of Part B, but adjusted depending on the density.
2. To determine the amount of material needed to fill the mold, I first poured water into the mold cavity until it was full. This helped me understand the exact volume required. I then poured the water into a measuring cup or weighed it to determine its volume in grams.
3. After measuring the required amount of Part A, I calculated how much Part B was needed. Normally, 10% of Part A’s weight would be correct, but because Part B has a different density (1.24 g/cc), I adjusted the weight accordingly using the following formula:
   
   Adjusted Part B (g) = (Weight of Part A / 10) × Density of Part B
4. In my case, the weight of Part A was 84.6 g. So I first calculated 10% of that (8.46 g), and then multiplied it by the density of Part B (1.24 g/cc). This gave me an adjusted value of approximately 6.77 g of Part B.
5. Final measurements used in the mixture:
   • Part A: 84.6 g
   • Part B: 6.77 g (adjusted based on density)

   

   It’s very important to mix the two parts thoroughly to ensure the silicone cures properly. I mixed them in a clean container for a few minutes, scraping the sides to avoid unmixed areas.



6. Once the mixture was ready, I poured it slowly into the mold to avoid trapping air bubbles. The mold had already been prepared with a release agent to ensure the final cast could be removed easily once cured.

7. After pouring, I let the silicone sit for ten hours, but the results were not good.

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.

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.

I was thinking about how to obtain a good result, so I decided to make a 3D printed mold in one piece. I waited for it to dry, and then I added more silicone on a flat surface to create a complete mold.

1. First, I measured the density using water.

To get a good result in this case, I mixed Component A correctly with Component B.

I used Flexible Silicone 950.

Link datasheet.


2. 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.
3. I mixed for 2 minutes and poured the silicone into my mold.

4. I waited 10 hours until it was ready.
5. Then, I added silicone on a flat surface and placed the first piece together with the second piece.
6. I waited 2 hours until it was ready.

7. Finally, I added my PCB, which you can see on my Final page.

Design

1. Sketched half of a cow's face.
2. Used the Mirror tool to create a symmetrical face.
3. Extruded the cow shape to make it 3D.
4. Created a rectangle around the cow and extruded it upward to form a box mold.

1. Opened Chitubox and loaded the STL file.
2. Centered the model on the build plate.
3. Ensured the flat side was touching the platform.
4. Added and adjusted supports.
5. Clicked Slice and saved the file to a USB stick.

1. Turned on the printer and inserted the USB.
2. Selected the file on the touchscreen and started the print.
3. Checked that the resin vat had enough resin.
4. Removed the print using a metal scraper.

1. Filled the container with 90%+ isopropyl alcohol.
2. Closed the lid and washed the part for 8 minutes.
3. Air-dried the part.
4. Replaced the container with the turntable.
5. Placed the dry part and cured it with UV light for 8 minutes.

1. Used Smooth-On 3030: 100% Part A and 10% Part B.
2. Measured volume with water and marked the level.
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 1.30 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.

The final mold captured the cow shape successfully.

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.