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Molding and Casting

Idea Development

I started this week without a very clear idea of what I wanted to create. I initially thought of making a candle—something with an unusual, organic shape. The concept that came to mind was a deflated balloon. I figured this could make for a fun candle, and it would also allow me to explore two-part mold making. The plan was to design a two-sided mold that would fit together, so I could pour in wax and create a hollow object.

Materials and Tools Used

Materials:

  • PLA filament (for 3D printing the mold negatives)

  • Food-safe silicone (for casting the mold)

  • Melted chocolate (for final casting)

  • Water (used unintentionally during cleaning and caused defects)

Tools and Equipment:

  • 3D printer (home setup, FDM type)

  • Silicone mixing containers and stirrers

  • Microwave (for chocolate melting)

Design Process

I modeled the deflated balloon in 3D and built a negative mold with two halves that could align and connect. I added features like a pouring channel and a vent hole, imagining how the wax would fill the shape.

However, midway through the design phase, I decided to scale down the model without considering how that would impact the functional parts of the mold. That turned out to be a key mistake. Once I printed the mold and poured the silicone, I realized the walls were too thin, the connecting elements were too small to be effective, and the vent merged with the pouring hole. Everything lost its structural integrity because of the scaling.

Manufacturing Challenges

Because I was sick that week and couldn’t go to the lab, I decided to work from home using what I had: a 3D printer, food-safe silicone, and basic materials. I printed the mold at home and cleaned it with water—but didn’t dry it properly. When I poured the silicone, the remaining water droplets left marks inside, creating unwanted impressions.

The silicone I used takes 10 hours to cure and is designed for food use, so instead of wax, I had an idea—why not cast chocolate instead?

First Casting Attempt: Chocolate Balloon

Switching to chocolate introduced a whole new set of problems. Chocolate isn’t very fluid when melted, and pouring it into a small two-part mold was extremely slow and difficult. I couldn’t see how much chocolate was inside, and because of the shape and the tight interior, the chocolate didn’t fill the mold properly. The cast was uneven and fragile, and overall, the process was frustrating and impractical.

Reflection and Redesign

Key lessons learned from the first prototype:

  • Do not scale down designs without considering the impact on wall thickness, connectors, and functional features.

  • Avoid working blindly with viscous materials like chocolate in closed molds(you need visibility and flow control).

  • Moisture inside the mold (from water cleaning) can leave defects in the silicone.

  • Working outside the lab significantly limits access to essential tools and quality control.

  • A two-sided mold is not ideal for chocolate casting due to visibility and pouring challenges.

Redesign decisions:

  • Switch to a single-sided mold with a wide open surface for easier pouring and drying.

  • Choose a new shape that supports both aesthetics and function.

  • Plan to embed ingredients like almonds or other chocolates inside the mold for added texture and flavor.

  • Design with food casting in mind from the start—prioritize usability over complexity.

Second Mold: Geometric Chocolate Form

For the second attempt, I redesigned the process entirely. Instead of sticking with a two-part mold, I opted for a one-sided mold, inspired by conventional chocolate molds. This change allowed for easier pouring, better control, and visual monitoring of the casting process.

Design Improvements

This time, the shape was geometric, more structured compared to the organic balloon form. I angled the walls of the mold to improve flow and demolding, aiming for better usability. However, I underestimated how complex the shape and forgot completely about the model undercuts. This introduced potential risks during the demolding process.

Molding and Casting

Fortunately, the mold did not break when removing it from the 3D-printed negative. The silicone cured properly, and there were no bubbles or defects in the surface—this time I made sure there was no moisture left during casting.

There were still some issues, though:

  • I ran out of silicone toward the end, leaving the top layer too thin.

  • Ironically, this “mistake” turned out to be useful: the thin layer made demolding easier, acting almost like a built-in release aid.

  • The result was a very large chocolate, which worked, but felt oversized. However, it made me realize that the mold could be reused for other applications, like ice cubes or layered desserts.

Reflections and Next Steps

Overall, this prototype was a step forward. The mold was functional, the casting was successful, and I managed to resolve earlier issues with moisture and scaling. However, it revealed some new limitations:

  • The mold was too bulky, using a lot of silicone.

  • Demolding was still difficult, showing that my draft angles weren’t generous enough.

  • I hadn’t fully avoided undercuts, which complicated removal.

  • For food-safe molds, thinner, more flexible silicone would help—but that requires a multi-piece mold system for complex shapes.

Future Improvements

Looking ahead, I plan to make several improvements based on what I’ve learned. First, I’ll incorporate greater draft angles to make demolding easier and more reliable. Avoiding undercuts will also be a priority, as they complicate the removal process and risk damaging both the mold and the cast. I want to explore designing modular, multi-part negatives that allow me to create thinner, more complex shapes while still ensuring the mold can be removed in pieces without tearing. Additionally, I’ll focus on optimizing material usage to reduce waste—especially when working with costly food-safe silicone.