8. Moulding and casting¶

This week’s tasks:¶

As a Group:

🐰 Review the safety data sheets for each of your molding and casting materials

🐰 Make and compare test casts with each of them

As a Individual:

🐰 Design a 3D mold around the stock and tooling that you’ll be using, mill it (rough cut + (at least) three-axis finish cut), and use it to cast parts.

Research¶

“Casting will typically involve metal, while molding focuses on plastics. In both cases, the melted material goes into a die or mold to create the final form. However, some other key differences in the process will change the final product. In molding, the material is injected into a form typically made of metal.”

Cast Materials¶

Material 1

Material name: Silicone rubber

⛔ Safety: 1. Used in a properly ventilated space. 2. Wear protective gloves and eye protection when using. 3. In case of skin contact, wipe it off with rubbing alcohol or hand sanitizer, then wash it with soapy water. 4. In case of eye contact, rinse with running water immediately for 15 minutes and seek medical attention. 5. Children should not use this product without adult supervision.

Process steps: Pour the Part A and B together, then stir the silicone rubber for about 5 mins. Make sure to stir the mixture thoroughly for better results.

🧐 Mix ratio (if applicable): 1:1

⏱️ Work time: 30 min ⏱️ Cure time: 3-6 hours

Material 2

Material name: RTV2 SILICONE RUBBER

⛔ Safety: safety glasses, long sleeves, and rubber gloves. However, it’s essential to note that latex gloves can interfere with the curing process of RTV-2 silicones, so opt for vinyl gloves instead.

Process steps: 1) Surface (Model) that silicone will be poured must be clean. • There shouldn’t any wet, dust or dirt.

2) Release agent for the surface is adviced. • Spray
• Brush
• Sponge

3) Silicone must be mixed at least 30 seconds before adding the curing agent. • Mixing process will increase the fluidity of the silicone. • Helps chemical components inside the silicone become homogeneous.

4) All preliminary work should be done before casting and casting should be completed without wasting time. • Enough amount of curing agentmust be added to silicone. • Ideal curing time that depends on the silicone and curing agent. In most of the cases it is better to wait for 8-12 hours. Silicones that vulcanized (cured)under or over this time may have slightly less performance. • Curing agent amount must be set according to the ambient temperature and moisture. • Curing and operation time shortens as the temperature and moisture rises. • More the curing agent amount faster the vulcanizing, less the curing agent amount slower the vulcanizing. • Precision balance is highly recommended to determine the right amount. If there is no access to any balance, tape measure or a syringe can be used, as well.

5) Silicone must be mixed well after adding the curing agent. • A low-medium speed mixer (paint mixer etc.) is recommended. • Mixing process, taking the silicone amount into consideration, should continue approximately for 1-2 minutes. • Important during the mixing process is to make sure that the curing agent penetrates the siliconecompletely and spreads homogeneously.

6) Removing of the air bubbles after the mixing process is essential. • Must be kept for 1-2 minutes inside the vacuum chamber for the best results. • If you have no access to a vacuum chamber one, vibration method can be used. • With a blowgun or by blowing, the evacuation of bubbles on the surface can be supported.

7) Silicone must not be touched after the moulding process until the vulcanizing (curing) is completed. • Vulcanized silicone can be released from the model. • For the best moulding performance, process should begin at least 24 hours after the vulcanizing is done. • It is recommended to rest the mould and cleaned at regular intervals between the castings if the offensive chemicals will be processed such as polyurethane.

🧐 Mix ratio: A:B - 1:1

⏱️ Work time: 30 - 40 mins ⏱️ Cure time: The catalyzed material will cure to a flexible rubber within 6 hours (or faster by different mixing ratio or room temperature), we advice you de-mold after 24 hours.

Material 3

Material name: Resin

⛔ Safety: Gloves, masks, and eye protection are recommended when working with resins to avoid skin contact and inhalation of fumes.

Process steps: Step 1 : Purchase the required materials and put on your personal protective equipment. Step 2 : Mix the resin and hardener in the suitable ratio. Step 3 : Add pigments or colours to it. Step 4 : Pour it in the mold. Step 5 : Cover it. Step 6 : Let it dry.

🧐 Mix ratio: 10:6

⏱️ Work time: 45 minutes ⏱️ Cure time: 24-48 hours

Material 4

Material name: Gypsum (standard plaster)

⛔ Safety: It is recommended to use Eye protection and gloves.

Process steps: collect into water (not reverse) in a clean bucket and use cool, clean water. Stop dosing when the powder exceeds the water level. After 1 minute of soaking, properly mix by hand or by mixer

🧐 Mix ratio: 1.25Kg of plaster for 1L of water. (Or 0.8L of water for 1Kg plaster.)

⏱️ Work time: 5 minutes ⏱️ Cure time: Initial: 5 minutes Final: 15 minutes

3D Design¶

I designed a medal with a star in the middle using tinkercad website.

🐰 Note that the cutter has the following dimension limitations:

The requirements for the design size are as follows: Smallest gap: 1.6mm (That’s the smallest milling bit) Design height max: 8mm Design width and length max: 60mm