Moulding and Casting

Group Assignment

1. Molding and Casting

Molding and casting is a manufacturing process used to copy shapes by using a mold.
Molding: making a negative shape (the mold) from an original object.
Casting: pouring a material into that mold to create a copy.
Molding and casting is a replication process:

- A mold = negative geometry

- A cast = positive reproduction

2. Materials

Molding and casting uses three main groups of materials. First, machinable materials like wax, foam, or MDF are used to mill the initial mold shape with a CNC machine. Second, flexible mold materials, mainly silicone rubber (such as products from Smooth-On), are poured over that shape to create a detailed and reusable negative mold. Finally, casting materials—like polyurethane resin, epoxy, plaster, or concrete—are poured into the mold to produce the final object. Each material is selected based on properties such as flexibility, curing time, strength, and ability to capture fine details.

Machinable wax Easy to cut, smooth finish Reusable (can be melted and recycled) Ideal for precise molds
RTV F-20 Plus Silicone RTV F-20 Plus is a room-temperature curing silicone with medium hardness and viscosity, offering high tear resistance.

I reviewed the silicone’s data sheet to understand its key properties and safety requirements. This helped me determine important parameters such as the correct mixing ratio, curing time, and working time (pot life), which are essential for a successful casting process. Additionally, the data sheet provided safety guidelines, including proper handling, recommended protective equipment, and ventilation requirements. Taking these factors into account ensured that the process was both safe and efficient, while also improving the quality and reliability of the final result.

Individual Assignment

3. Mold Design

I decided to design a pawn since it’s a standard 3D model, so I used Onshape for the design as well.

After completing the sketch, I used the revolve tool to create the pawn model.

I created two solid blocks and used the subtract tool in Onshape to generate the mold cavity.

4. Mold Printing

I printed both sides in order to get a complete mold.

5. Preparation for Casting

After printing the mold, I organized the workspace and gathered all the materials needed for the casting process.

I poured a sufficient amount of RTV F-20 Plus silicone into a glass container, enough to fill the entire mold cavity.

I used a balance to measure the correct proportion of silicone; as shown in the picture below, it weighs 388 grams.

According to the instructions, we need to add a catalyst equal to 3% of the silicone’s weight.That corresponds to approximately 11.64 grams of catalyst.

I added the catalyst to the silicone and mixed thoroughly to ensure it was evenly distributed.

We need to mix the silicone and catalyst thoroughly to ensure even distribution.

After that, I assembled the previously printed mold pieces and secured them with a clamp to hold the joint in place.

Finally, I poured the mixed silicone into the mold cavity, ensuring it filled all areas and avoiding air bubbles.

After allowing the silicone to cure and confirming it had set properly, I opened the mold and removed the finished part.

Next, I demolded the part and examined the result—it was very uniform with a smooth, high-quality surface.

After trimming and cleaning off the excess material, I obtained the final product.

6. Learnings

I didn’t design the mold with built-in fastening or alignment features, so I had to rely on a clamp to keep the parts together. This worked, but it made assembly less precise and more time-consuming. In future designs, I would include proper locking or guiding elements to improve alignment and stability.

I learned that once the silicone is mixed with the catalyst, it must be poured quickly because the curing process starts immediately. If I wait too long, the mixture begins to thicken and becomes harder to work with, which can affect the final quality. Planning the workflow in advance is essential to avoid delays during this step.

7. Files

Here are the files available for download.

1. STL 3d Model: 3d Model STL.rar

2. STL Mold parts: Mold parts STL.rar