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14. Molding and Casting

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Group Assignment

You can find more details on our lab site: TechWorks - Molding and Casting

This week was so nice; I worked with new things—“chemicals.”

  • Learning Outcomes:

Molding: Molding is the technique of forming a hollow cavity (called a mold) that mirrors the exact shape of the object to be produced. This mold serves as a negative imprint of the desired item. Once created, the mold is filled with a suitable material—such as liquid plastic, rubber, or molten metal—that can conform to the mold’s shape. After the material cools or solidifies, it adopts the form of the mold.

Casting: Casting refers to the act of pouring a fluid material—typically a liquid metal, plastic, or resin—into a pre-made mold. The material flows into every part of the cavity, taking on its shape. As it solidifies, the material becomes a solid replica of the intended design. This method is especially useful for producing multiple identical items efficiently.

Positive Mold: A positive mold is a replica that matches the shape and details of the original object. It serves as a master model for creating molds or final copies.

Negative Mold: A negative mold is the inverse of the original object, capturing its shape as a hollow cavity. It’s used to cast replicas by filling the void with a material.

Pot Life: Pot life, or working time, is the duration during which a mixed material (like resin or plaster) remains usable before it starts to harden. It depends on the material and environmental conditions such as temperature and humidity.

Cure Time: Cure time is the total time needed for a material to fully harden after mixing. It varies based on the material type, quantity used, and environmental factors.

  • My contribution:

I made test samples using different materials: Dragon Skin, Liquid Plastic 305, and Hydro Stone Super-X.


Individual Assignment

CAD design

I designed a FAB 2025 medal using SolidWorks.


Molding and Casting Process (Positive → Negative → Positive):

Positive (Wax Model): Start by shaping the desired object using wax. This serves as the original positive model.

Negative (Dragon Skin Mold): Cover the wax model with Dragon Skin silicone to create a flexible mold, capturing all surface details. Once cured, the wax is removed, leaving a negative cavity.

Final Positive (Plastic Casting): Pour liquid plastic into the silicone mold. After it solidifies, remove the final cast—an exact plastic replica of the original wax model.

Molding “Positive”

I used a CNC machine for the molding process.

The pictures below describe the process:














Casting “Negative”

After cutting the part, I wanted to know the volume of my medal to determine how much material I would use. So I filled it with water and measured it in kg.


It’s almost 60g.

After determining the amount, I started measuring the actual material Dragon Skin. I followed the procedure described in this link.


  • According to the datasheet, it’s 1A:1B by weight or volume, so I mixed 30g of material A with 30g of B.


  • The vacuum was used to remove any bubbles.


Here I added Vaseline, based on my teammate’s suggestion, so the material could be removed easily.

I used this machine (provides air with high pressure) to take the material off without losing any details.

The result:

Isn’t it nice?

Final Positive

I used Liquid Plastic 305 for the positive cast of my FAB medal design. I followed the procedure described in this link.

1A:1B by volume or 100A:90B by weight. I chose to use weight, as with all previous processes, so I mixed 14g of material A with 13g of material B.

Process: - Shook both material A and B very well before opening.

  • Mixed 14g:13g for 1 minute.

  • Poured the mixture into the wax mold.

  • Left it at room temperature for around 30 minutes until the material hardened.




Issues

In my first positive cast, I had an issue due to using a food color with Liquid Plastic 305.
After around 5 minutes of mixing, the mixture turned into a sand-like texture and became hotter.



Solution

Our lab instructor advised me to use a powder color to prevent any chemical reaction, and it worked.

The final result:

Files: