Week 13 - Molding and Casting
Published on: June 03, 2025
Custom Vegan Gummy Bear Mold
My goal for the Assignment Molding and Casting is to create a reusable, food-safe silicone mold to make vegan fruit gummy bears. To achieve this, I will design a positive 3D model of the gummy bears, 3D print it, and embed it inside a laser-cut mold box to cast the silicone. The final silicone mold will then be used to cast gummy bears using an agar-agar recipe.
Process Overview
- Designing the Mold Positive (TinkerCAD): The positive shape of the gummy candy is modeled using a CAD tool such as TinkerCAD. This model defines the final geometry of the castable shape.
- 3D Printing the Positive: The CAD model is 3D printed using a suitable material like PETG. Since FDM printing often results in visible layer lines, post-processing such as sanding may be required to achieve a smooth surface finish.
- Creating the Mold Box: A mold enclosure is designed using a parametric box generator and cut from materials such as 3 mm acrylic. The box serves as a container for the silicone and should fit tightly around the printed part.
- Silicone Casting: The printed positive is placed inside the assembled mold box. A food-safe, two-part silicone is then poured around the positive to form the negative mold.
- Demolding: After full curing, the mold box is disassembled and the 3D print is carefully removed. The silicone mold is then cleaned and prepared for casting.
- Casting the Gummies: A vegan gummy mixture—typically made with agar-agar and fruit juice—is poured into the silicone mold to create the final edible pieces.
Design the Mold Positive
I designed the positive model for my silicone fruit gummy mold using TinkerCAD, an easy-to-use browser-based 3D modeling tool. My goal was to create a simple but fun shape – a star – and replicate it multiple times on a flat base to prepare it for molding.
I started by dragging a flat box shape onto the workplane and resized it to create a baseplate with dimensions around 90 x 90 x 3 mm. This would serve as the foundation for the entire positive mold and ensure that all star shapes sit on the same level.
Next, I added a star shape from the basic shape menu, set its dimensions to approximately 18 x 18 x 6 mm, and placed it on the baseplate. I duplicated the star eight times and arranged them in a 3 × 3 grid pattern. To ensure perfect alignment and spacing, I used TinkerCAD's built-in "Align" and "Distribute" tools.
Once the stars were correctly positioned and centered on the baseplate, I selected all objects and used the "Group" function. This merged the stars and the base into a single solid object — making it ready for 3D printing and casting.
As the final step, I exported the grouped design as an .STL file, which I later used for FDM 3D printing. The exported file contains the full positive form that will be used to create the negative cavity in silicone.
I created an 80×80×2 mm baseplate to serve as the foundation for my mold.
A single star shape was added and scaled to approximately 6 mm height — the planned gummy thickness.
I duplicated the star and placed it across the baseplate to begin forming a grid layout.
TinkerCAD's alignment tool helped evenly distribute and center the stars precisely.
The final layout includes 9 stars, neatly arranged in a 3×3 grid, all grouped with the baseplate.
Once finished, I exported the model as an .STL file for 3D printing.
3D Print and Post-Processing
Since I haven't been to the Lab for a while, I unfortunately wasn't able to 3D print the mold.
Creating the Laser-Cut Mold Box
To hold the 3D printed star mold in place while pouring silicone, I needed a custom-sized mold box. For this, I used a parametric box generator called MakerCase to quickly generate a laser-cut-ready design.
I measured the dimensions of my printed mold base (approximately 80 × 80 mm) and added a small margin on each side to give the silicone enough wall thickness. I entered the final internal dimensions into the box generator and set the material thickness to 3 mm, since I used standard acryl for laser cutting.
The box generator created a downloadable .SVG file with finger joints that can be assembled easily.
I started with the MakerCase interface and selected a simple open-top box template.
I set internal dimensions to 92×92×20 mm, allowing space for silicone walls and height clearance.
The software generated SVG plans with finger joints, ready to be laser cut from 3 mm acrylic.
Next time I am in the Lab, I am going to laser cut the frame.
Silicone Casting
Once the positive mold has been 3D printed and the laser-cut mold box is assembled, I will be ready to pour the silicone into the mold. The silicone will flow around the star shapes and solidify into a flexible, food-safe casting mold.
Gummy Casting
The next step will be to cast the vegan fruit gummies into the finished silicone mold using an agar-agar and juice mixture. I'm really looking forward to seeing the final results!
