Molding + casting
Saco notes
Saco took us through our Thursday lesson. His push bike wheels are a great example of what can be done with molding and casting.
Below are some useful resources on molding and casting.
Group project
- review the safety data sheets for each of your molding and casting materials
- then make and compare test casts with each of them
- compare mold making processes
The beginning of this week's group project was to read over and compare the data + technical sheets of the different casting materials.
Based on our findings, we can make a decision about which casting materials to use for this week's individual project/s.
| TYPE | POT LIFE | CURE TIME | STRENGTH |
|---|---|---|---|
| Clear Flex 30 (urethane rubber) | 15 mins | 16 hrs | Shore A: 30 |
| Ure-bond II (urethane adhesive) | 5 mins | 24 hrs | Shore A: 85 |
| Ure-bond 90 | 8 mins | 16 hrs | Shore D: 90 |
Clear Flex 30, safety specs:
Ure-bond II, safety specs:
Ure-bond 90, safety specs:
For the group project, we decided to each test out three different materials. All of the ones I chose were the most toxic ones, so, when I read the data sheets, I judged their dangerousness relatively. I think I didn't take the precautions seriously enough.
For instance, the Urethane agents, why are they toxic? (I asked AI):
The toxicity is mainly due to the presence of isocyanates and other reactive chemicals in the mix. Isocyanates are known for causing respiratory irritation, sensitization.
- When inhaled, isocyanates irritate and inflame the lungs, causing coughing and breathing difficulty.
- They can trigger immune sensitization, leading to occupational asthma—even at very low exposures.
- Repeated exposure may cause chronic bronchitis, lung damage, or hypersensitivity pneumonitis.
- Severe reactions can include airway narrowing and potentially life-threatening asthma attacks.
- Some isocyanates are suspected carcinogens, increasing long-term health risks.
Group project results
Individual project
For this week's individual project I am having a bit of trouble deciding what to make. Given that I have some experience with resin casting, I would like to try something more complicated. My experience in previous suggests that maybe that's not the best idea. Secondly, I would like to focus more time for designing my final project.
For my final project, I believe a non-slip / textured silicone layer could be useful for creating friction that might help with final project.
I think I'll make a simple shape to mill a mold of - so that I can cast the local orange.
And I'll design a simple textured mat that I can make a negative mold of and cast silicone / rubber in.
3D design + milling
NB. From Saco's notes: I used a low speed of 10 mm/s to reduce the effect of the shock wave that occurs due to absence of deceleration of the ShopBot axis drivers.
Three way mold: mill a positive on the ShopBot, cast a negative mold from that and use it again to make a positive.
Hard negative to cast soft positive. Choose materials that won't stick together.
Runners and Vents
Test amount of material needed by filling the mold with water and then pouring that into cups.
For the nonslip mat, my design considerations were primarily around what the repeated object / texture should be for the face. I would like to avoid having too many individual small parts to mill as that would increase the time it takes to complete the job. In the same way, I would like to avoid having too much negative space, that the milling machine must cut out.
I thought that this week could be a good way to sharpen my CAD skills -- as that's an area I'm not too comfortable in. A pyramid object, for the pattern would be useful for me to learn how to design. Or objects with curves.
However, upon further review a non-slip mat would only be 2D, and I need to make a 3D object.
How to get the orange to float?
Have it suspended by a pin.
How to make a sphere with a trimmed bottom How to make objects solid in Fusion How to make sure the orange doesn't create bubbles when the resin is poured in How to make the sprue and air valve?