Fab Academy 2025

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Week 14 - Molding and casting ​

Assignments ​

Group Assignment ​

  • Rreview the safety data sheets for each of your molding and casting materials,then make and compare test casts with each of them compare mold making processes

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 toolpath,and use it to cast parts
  • Extra credit: use more then two mold parts

Group Working ​

My group work is attached here: https://fabacademy.org/2025/labs/unnc/assignments/week14/week14.html

Individual Working ​

This week, I experimented with two mold-making methods: one using silicone to create molds, and the other using CNC machining to produce steel molds.

Silicone mold production ​

Keychain Modeling ​

I first completed the 3D modeling of the keychain using Fusion 360. The design features a simple geometric outline, with a reserved hole for attaching a strap.

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3D Printing ​

Once the design was finalized, I printed the keychain model using a 3D printer. The resulting object had a good surface finish and clearly defined details. alt text

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Testing 8015AB ​

I planned to use 8015AB (a silicone surface treatment agent) to improve surface adhesion before coating or printing.

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Mixing Test: ​
  • Mixed 8015A and 8015B in a 1:1 ratio.
  • Stirred evenly and observed the surface reaction and film-forming properties.

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  • After the AB resin was fully cured and demolded, a large number of bubbles were present on the surface.

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  • To improve the final finish and reduce air entrapment, I plan to use a vacuum pump for degassing in future tests.
Experiment Issues: ​

Due to the lack of a precise electronic scale, the mix ratio was inaccurate. As a result, the mixture failed to solidify or form a proper film — the surface remained sticky, indicating a significant deviation from the optimal AB ratio.

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Silicone mold making ​

To further process the keychain, I attempted to make a negative mold using silicone, for replication or casting.

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Reflection on failure ​

  • The curing agent was insufficient, resulting in prolonged uncured silicone.
  • Severe flow and bubble formation occurred.
  • Lessons Learned:
    • Always use a measuring cup or electronic scale to ensure accurate proportions.
    • Enhance defoaming steps during silicone preparation.

I experimented with a new process that combines 3D printing technology with hot press molding to fabricate a composite material of polycarbonate (PC) and high-temperature carbon fiber.

Metal mold ​

Material Introduction ​

Polycarbonate (PC) is a colorless, transparent thermoplastic engineering plastic known for its high impact strength, excellent heat resistance, and good molding processability. Its glass transition temperature is approximately 147°C, with a melting point between 220–230°C, making it suitable for secondary processing via hot press molding.

High-temperature-resistant carbon fiber (24K) is a high-strength carbon fiber bundle with outstanding mechanical properties and heat resistance, widely used in reinforced composite materials.

Experimental Steps: ​

  1. Mould processing

The processing results are as follows:

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  1. PC Sheet Preparation
    First, FDM 3D printing technology was used to print two flat PC sheets.
  • Model slicing and uploading:

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  • After printing, uniformly thick and smooth PC sheets were obtained:

alt text 2. Material Preparation
The required materials included molds, PC sheets, carbon fiber, and clamps:

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alt text 3. Hot Press Molding
The carbon fiber was evenly arranged between the two PC sheets to form a "sandwich structure." The assembly was then placed into the mold and secured with clamps to ensure tight bonding during heating. A heat gun was used to heat the mold for 3–5 minutes, allowing the PC material to fully soften and fuse with the carbon fiber:

  1. Cooling and Demolding
    After heating for 3–5 minutes, molten material was observed overflowing from the mold surface, indicating that the PC had reached a softened state and begun to flow:

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  • After cooling for a period, the mold was disassembled, revealing the fully formed material:

  • Comparison between finished product and PC material after processing:

alt text It can be observed that the originally opaque material became transparent after processing, with significantly improved hardness and no internal bubbles.

Reference: ​

The reference and design files are listed below: