13. Molding and casting¶
Group Assignment¶
- Review the safety data sheets for each of your molding and casting materials
- Make and compare test casts with each of them
- Compare printing vs milling molds
Overview¶
We molded and casted many different materials through a few different processes this week. We each created molds in machineable wax to experiment with.
Safety¶
Mold Star 31T (Parts A and B) is a silicone elastomer and is not considered hazardous. The material is broadly considered benign for laboratory use. Even so, we take measures to ensure the compound does not get smeared in places it shouldn’t. We wrapped the lab table in newspaper and plastic wrap, and used gloves and safety goggles when handling the material.
Smooth Cast 320 is a bit more dangerous to handle and requires more safety considerations. Part A contains MDI, an isocyanate. It can cause skin, eye, and respiratory irritation, and it may trigger allergic skin reactions or asthma-like symptoms if inhaled. It is harmful if inhaled and carries a warning as a suspected carcinogen with prolonged exposure. As a precaution, we opened the windows to ensure adequate ventilation and wore protective gloves and face shielding eye goggles. When finished, we made sure to properly dispose of any contaminated material.
First Aid Measures - Skin Contact: Wash the area thoroughly with plenty of soap and water for at least 15 minutes. - Eye Contact: Rinse cautiously with water for at least 15 minutes, removing contact lenses if you can do so safely. Get medical attention if irritation develops. - Inhalation: Move the person to fresh air immediately and keep them comfortable for breathing. - Ingestion: Do not induce vomiting. Give small quantities of water to drink and contact a physician immediately.
The remaining materials used for the biomaterial were common household kitchen staples, including coffee grounds, eggshells, vinegar, glycerin and potato starch. Common sense when handling these materials is exercised, as well as the same precautions for the Mold Star in terms of not getting it where it shouldn’t be.
Results¶
Youssef’s silicone and resin casting results¶
I was the first one in the lab to finish the silicone mold and resin cast, so I am adding the practical notes here for the group page.
For the silicone mold, I used Mold Star 31T in a CNC-machined machinable wax mold. I measured the wax cavity with water first, then dried it before pouring. Mold Star 31T mixes 1A:1B by volume or weight. I used about 30 ml (30 g) of each part, mixed slowly, scraped the cup, and poured before the 5 min pot life was over. The listed cure time is about 23 min, but I left it for about an hour. The silicone mold came out clean and flexible.
For the resin cast, I used Smooth-Cast 320 inside the Mold Star 31T mold. This is where I made the useful mistake. Smooth-Cast 320 mixes 1A:1B by volume, but 100A:90B by weight. I measured the first attempt like equal weight, so the surface finish was bad. On the second attempt I used the correct weight ratio and the result was much cleaner.
Smooth-Cast 320 also has a very short pot life, about 3 min, so the mold, clamps, cups, stir stick, gloves, and covered table all need to be ready before mixing. Any silicone or resin cup should stay on the table covering because drips can cure onto the table, contaminate the work area, and make cleanup much worse.
| Material | Result | Timing note | What I would tell the next person |
|---|---|---|---|
| Mold Star 31T silicone | Clean flexible mold | 5 min pot life, listed 23 min cure, I left it about an hour | Measure the wax cavity first, dry it fully, mix slowly, and pour in a thin steady stream |
| Smooth-Cast 320 resin | First cast had a bad finish, second cast was much cleaner | 3 min pot life, about 7-10 min cure depending on the cast | If measuring by weight, use 100A:90B, not equal weights |
Troubleshooting Notes¶
| Problem | Solution |
|---|---|
| Smooth-Cast 320 first cast had a bad surface finish | Use the product ratio correctly. It is 1A:1B by volume, but 100A:90B by weight |
| Silicone or resin cups can drip onto the table | Keep every cup and mixed material container on the table covering until cleanup |
AI usage¶
Youssef used AI to help turn his individual casting notes into a shorter group-page summary.