14. Molding and Casting¶
Weekly Assignment:¶
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
Individual assignment:
- Design a mold around the process you’ll be using, produce it with a smooth surface finish that does not show the production process, and use it to cast parts.
Design¶
My mold idea was a tray to make yogurt bark. Because my end mold is supposed to be a hard one, I decided to 3D print my cast. That meant I had to design it in Fusion 360.
Print Settings¶
To make sure my final print was smooth and layer lines could not be seen, I made some changes duing slicing in Bambu Studio.
For one, I changed the layer heights from 2 mm to 0.08 mm to make the layers thinner and therefore less visible.
I increased the sparse infill because I felt like that would give it more support and make the top and middle layers more even.
I also found out about the Seam setting, and I changed it from Aligned to Nearest to make it more seamless.
Molding¶
While it was printing out, the spool ran out of filament and I had to change it to another one of a different color. That's why the coloring looks a bit weird and makes it seem streaky.
When I was pouring in the material, Smooth-Sil 940, of my mold, we were running low on the material. I was pouring it into a much larger container, so to prevent extra material from being used, I blocked off the other side with cardboard by hot gluing it down. Even do, I barely had enough and had to redistribute it using popsicle sticks, which ended up making it look lumpy but it still worked and covered evrything it needed to.
This was my final mold with the 3D print taken out.
I trimmed the edges as well so they weren't as messy.
Casting¶
We did not have any casting materials that were food-safe, so I had to use what was available that wasn't. What I ended up using was Smooth-Cast™ 65D (I believe), with a pot lift of 5 minutes and a cure time of 15-20 minutes. It cured really quickly and I could visisbly see the material becoming more opaque as it hardened. It was also an intensely exothermic reaction and was very warm to the touch.
This was the final product and I ended up repurposing it as a jewelry holder for earrings and what not. If I have time later and materials, I'll still try to make the yogurt bark mold.
Group Assignment¶
Our group assignment was to review the safety data sheets for each of your molding and casting materials, make and compare test casts with each of them, and compare printing vs milling molds. Here is the documentation on our group site.
Individual Contribution¶
My role was to review the safety data sheets for each of our molding and casting materials.
Machining Wax Datasheet¶
For the machining wax, I referred to this source of information.
Its main features including being non-abrasive, self-lubricating and pretty user-friendly. It is ideal for producing accurate reproductions.
As for machining guidelines,
- Spindle Speed: 3,000 RPM
- Feed Rate: 100 in./min
- Finishing: Spindle Speed: 8,000–10,000 RPM
- Feed Rate: 40–100 in./min
Data obtained using a ½” ball end mill.
In terms of physical properties
| Property | Value |
|---|---|
| Specific Gravity | 0.94 |
| Ash Content | 0.010% |
| Hardness (Shore D) | 43 |
| Softening Point | 157°F |
| Volumetric Shrinkage | 7% |
| Viscosity @ 160°F (CPS) | 30 |
SORTA-Clear 37 Datasheet¶
SORTA-Clear 37 (Silicone Rubber) SORTA-Clear 37 is platinum-cure silicone. It has a 25-minute pot life and cures in about 4 hours at room temperature. It’s medium-firm with a Shore A hardness of 37, which means it’s flexible but not super soft. It’s certified food-safe and skin-safe, so you can use it for chocolate molds or wearable items. It mixes 1:1 by volume, so no scale is needed, and it has very low shrinkage. You should avoid using latex gloves or anything with sulfur nearby, as those can inhibit the silicone’s ability to cure. Vinyl gloves are safe. Also, make sure your space is well-ventilated and wear gloves and eye protection when mixing. Users should operate in a well-ventilated area to avoid inhaling vapors or mists. Vinyl gloves are recommended, as latex gloves can inhibit the curing process . Additionally, wearing safety glasses and long sleeves can help minimize contamination risks.
Smooth-Cast 65D¶
Smooth-Cast 65D (Semi-Rigid Urethane Resin) Smooth-Cast 65D is an opaque, fast-curing resin that’s tougher than most plastic. It’s often used for things like props, prototypes, or casting solid parts in molds. It mixes easily at a 1:1 ratio by volume and has a super short pot life of just 2.5 minutes, so you need to work fast. It sets up solid in about 10–15 minutes. With a Shore D hardness of 65, it’s semi-rigid — not rubbery but not brittle either. It’s moisture-sensitive, so make sure your workspace is dry and not humid, and mix quickly to avoid bubbles. It gives off a lot of heat while curing, so definitely wear gloves, safety goggles, and work in a well-ventilated area (or use a respirator for large casts).
Smooth-Cast 65D is not food or skin-safe, and you should not use it in any application that involves body contact or ingestion. Due to its chemical composition, it’s essential to handle this material with care. Users should work in a well-ventilated area to avoid inhaling fumes, which can be harmful. Wearing protective gear, including safety glasses, long sleeves, and rubber gloves, is recommended to prevent skin and eye contact. It’s also important to note that the resin is moisture-sensitive; exposure to atmospheric moisture can affect the curing process and the quality of the final product.
Applying a suitable release agent to molds can facilitate demolding and prevent the resin from sticking to surfaces. After curing, castings may be hot to the touch and could cause skin irritation; allowing them to cool to room temperature before handling is smart. Proper storage of the resin in a warm environment (around 73°F or 23°C) and sealing containers tightly after use will help maintain its usability and prevent degradation.
Overview¶
This week was another one of the fun-type weeks because I was able to make something purposeful in daily life, which is always nice. Even though it didn't fully go as expected and I had to pivot with what I ended up doing with it, it was a good experience learning about how to mold and cast. In the past the closest I'd done to molding or casting was in 5th grade where I made plaster hands. I learned to be very aware of the instructions, probably because that was also my group assingment, and safety precautions regarding such chemicals.
Files¶
Design: