Week 14 Moulding and Casting

This week was an exciting and hands-on journey into the world of mold design and casting techniques. From understanding material safety to producing clean, functional parts, I gained valuable insights into both the creative and technical sides of the process.

Learning Objectives

👥 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.

Learning highlights

Project Presentation

1.1Food-grade Silicone

Food-grade silicone is a polymer material known for its safety, non-toxicity, resistance to high and low temperatures, and good flexibility. It is widely used in kitchenware, baby products, and medical devices.

👉 Datasheet

• Mixing Ratio: 1:1 (Part A : Part B)
• Hazards:
  • Moisture absorption can lead to harmful gel formation.
  • Fine dust may cause respiratory issues.
  • Rare skin allergies possible.
• Precautions: Use mask, gloves, goggles; ventilate the workspace; avoid ingestion.

Material Properties

Toxicity	Low toxicity
Color	Translucent
Curing time	About 8 hours
Weight mixing ratio	1:1
Reaction status	No significant heat generation
Advantages	Safe, non-toxic, suitable for food-contact molds, good elasticity
Disadvantages	Long curing time, surface details may not be very clear
Safety precautions	Wear gloves, avoid contact with eyes and skin
Usage process	Stirring may produce bubbles, defoaming process is slow
Bubble level	Medium bubbles
Defoaming level	Defoaming is slow

1.2 Epoxy Resin

Epoxy resin is a common thermosetting plastic known for its excellent adhesive properties, mechanical strength, chemical resistance, and electrical insulation performance.

👉 Datasheet

• Mixing Ratio: 1:3 (Part A : Part B)
• Mixing Instructions: Stir thoroughly for 5 minutes until the mixture is uniform with no stringy or fibrous texture. Pour directly into the mold immediately after mixing. Do not leave the mixture in the container waiting.
• Layering for Thickness:If casting thick layers, use a layering process based on the surface area. For regular resin tables, pour layers less than 2 cm thick at a time. Wait for the first layer to fully cure before pouring the next layer. Repeat this as needed.The best results occur when the ambient temperature is controlled below 25°C.
• Important Reminder: When mixing larger quantities, maintain the same base ratio accordingly. The Ultra Clear Crystal Resin and River Table Special Resin have different formulas, so use the correct ratio for each resin. Do not arbitrarily change the proportions.
• Hazards:
  • Skin irritation and potential dermatitis.
  • Vapors irritate eyes and lungs.
  • Possible allergic reactions.
• Precautions: Use PPE; ensure ventilation; avoid skin contact; follow safety instructions.

Material Properties

Toxicity	Moderate, may release volatile organic compounds
Color	Transparent, can add colorants
Curing time	About 24 hours
Weight mixing ratio	3:1
Reaction status	Slight heat generation
Advantages	High transparency, suitable for making detailed molds or accessories
Disadvantages	Strong odor, long curing time, high hardness
Safety precautions	Operate in a well-ventilated environment, wear gloves and a mask
Usage process	Few bubbles during stirring, uniform stirring has a significant impact on curing results
Bubble level	Low bubbles
Defoaming level	Good defoaming

1.3 Gypsum

The main component of plaster is calcium sulfate (CaSO₄). Depending on its water content, it is classified into raw gypsum, hemihydrate gypsum, and anhydrite. It is widely used in construction, medical applications, and crafts.

👉 Datasheet01 Datasheet02

• Mixing Ratio: 100g Plaster : 33g Water
• Hazards:
  • Dust inhalation may affect the lungs.
  • Wet plaster can irritate skin.
  • Hot plaster can cause burns.
• Precautions: Wear mask, gloves, goggles; avoid direct contact; work in ventilated areas.

Material Properties

Toxicity	Low
Color	White
Curing time	About 1 hour
Weight mixing ratio	10:3 (mix with water until no granules)
Reaction status	Slight heat generation
Advantages	Quick curing, low cost, suitable for rapid forming
Disadvantages	Brittle, not suitable for detailed mold making
Safety precautions	Wear a dust mask, avoid inhaling dust
Usage process	Stirring tends to produce bubbles, rapid curing affects defoaming
Bubble level	Medium-high bubbles
Defoaming level	Poor defoaming

2. Test Casting Comparison

Material	Mixing Ease	Detail Resolution	Curing Time	Flexibility	Safety Level	Notes
Food-grade Silicone	Easy	Excellent	~8 hours	High	High	Best for food-safe and flexible molds
Epoxy Resin	Moderate	Very High	~24 hours	Rigid	Low	Best finish, but hazardous
Gypsum	Very Easy	Good	~1 hours	Brittle	Moderate	Fast and low-cost option

3. Mold Making: 3D Printing vs CNC Milling

Method	Time	Surface Finish	Material Compatibility	Cost	Notes
3D Printing	3-5 hours	Layered lines	Great with silicone, plaster	Low	Ideal for complex shapes
CNC Milling	1-2 hours	Smooth	Wax, wood, foam	Higher	Best surface quality, 2.5D shapes

👤 Individual Assignment

5. 3D Printing

5.1 Fusion 360 Design-Floral Earrings

The floral earring model was created using Fusion 360. The final 3D model presents an elegant petal-like structure with a well-balanced overall design.

Downlode

File.STL this week File.STL this week

5.2 3D Printing Design

Printing Process

The final model was exported in STL format and processed using slicing software. The earrings were printed with an FDM 3D printer using PLA filament.

G code this week

To achieve higher detail, the layer height was set to 0.1 mm, and the print speed was set to 30 mm/s.

3D master mold

5.3 Molding and Casting

1. I mixed Part A and Part B of the silicone in a 1:1 ratio, so the total weight after mixing was 66 grams. Then, I stirred slowly to prevent the formation of air bubbles.

2. Let it sit for 8 hours and wait...

3. After the silicone mold was poured, I used plaster powder to make earrings. The materials I prepared were as follows:

4. The ratio of plaster powder to water was 10:3. I slowly mixed the appropriate amount evenly and poured it into the silicone mold.

5. Let it sit for one hour.

6. Paint the earrings.

7. Assemble the earring components, including clips, connectors, etc.

📌 Conclusion

This week's assignment helped us understand the properties, safety considerations, and performance of different casting materials. We learned how mold-making techniques affect the outcome and quality of the final cast. Silicone stood out as the safest and most flexible material. While 3D printing is more accessible, CNC milling provides superior finish for industrial applications.