- 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.
Week 13. Moulding and Casting
Group Assignment – Molding and Casting
Group Members:
- Sandra Hipatia Núñez Torres
- Manuel Ignacio Ayala Chauvin
Objective: Apply molding and casting techniques using plaster, silicone rubber, and epoxy resin. Explore mold manufacturing methods and compare CNC machining vs. 3D printing.
We started the week by diving into the technical and safety data sheets of the three main materials we would use: plaster, silicone rubber, and epoxy resin. It was fascinating to discover how each one behaves differently in terms of mixing, curing, and safety.
We reviewed the safety and technical data sheets for plaster, silicone rubber, and epoxy resin. Each one had unique properties for mixing, curing, and handling. We also made comparison casts to analyze their behavior and results.
During our group work, we analyzed three essential materials used in molding and casting:
- Plaster (Yeso)
- Silicone Rubber
- Epoxy Resin
We examined the technical data sheets of each material, focusing on physical properties, mixing and curing times, and safety guidelines.
Plaster
Composition: Calcium sulfate hemihydrate (CaSO₄·½H₂O).
Mix ratio: 80% plaster and 20% water, mixed until smooth and lump-free.
Drying time: Ideally 8 days, though we used it after 4 days due to time constraints.
Silicone Rubber
Properties: Flexible, tear-resistant, excellent for capturing detail.
Curing time: 7 hours for solidification, 12 hours for complete drying.
Epoxy Resin
Use: Applied inside silicone molds for final casting.
Working time: 20 hours to solidify, 72 hours for full cure.
1. Preparation of Plaster Blocks
We started by preparing the plaster blocks with an 80/20 ratio of plaster to water. The mix was stirred until homogeneous, free of clumps or dry particles. We poured it into plastic molds and allowed it to dry.
The recommended drying time is 8 days; however, we accelerated the process to 4 days due to time constraints, which required extra care during handling.
2. Machining of Custom Designs
Each team member selected a personal design:
- Sandra: An elephant – symbol of memory and strength.
- Manuel: A structural support – functional and precise.
3. Silicone Mold Creation
We poured silicone rubber over the machined models to create flexible molds. Technical data sheets indicated a solidification time of 7 hours and demolding readiness after 12 hours of curing.
4. Resin Casting
We cast epoxy resin into the silicone molds. The resin has a 20-hour solidification period and requires a full 72 hours to cure completely.
5. Results
The final products were:
- A resin elephant (Sandra)
- A functional support in resin (Manuel)
6. Comparison: 3D Printing vs. CNC Machining
| Aspect | 3D Printing | CNC Machining (used) |
|---|---|---|
| Detail Precision | Very High | High (tool-limited) |
| Production Time | Slow (depending on model) | Moderate |
| Material Cost | High (filaments) | Low (plaster) |
| Mold Reusability | Limited | High with silicone molds |
| Versatility | High (complex forms) | Medium (simple geometries) |
Conclusion
This technical analysis was key for selecting and applying the materials properly. Reviewing the data sheets ensured that the molding and casting process during Week 13 was both safe and efficient, allowing us to produce functional and well-formed pieces.
This group project allowed us to explore and understand the complete workflow of molding and casting, from material preparation to final product fabrication. Through hands-on experimentation with plaster, silicone rubber, and epoxy resin, we gained valuable insights into the properties, behavior, and handling requirements of each material.
By dividing responsibilities and working collaboratively, we not only produced two functional and detailed resin pieces—a figurative elephant and a structural support—but also reinforced our ability to manage timelines, follow technical datasheets, and adapt when faced with time constraints.
The comparison between CNC machining and 3D printing as mold fabrication methods also enriched our understanding of digital fabrication strategies, allowing us to weigh the pros and cons of each depending on the design and production context.
Individual Assignment: Mold Design and Casting
Feeling more confident, I designed a keychain mobile holder from scratch in Fusion 360. I paid attention to wall thickness, cavity supports, and usability. The mold was milled into a plaster block I prepared myself with the standard 80/20 mix.
I cast the mold using silicone rubber and filled it later with epoxy. This second project gave me more control and let me apply everything I had learned so far.
Introduction
In this individual practice of the digital fabrication course, I developed a complete design, modeling, and casting process for a functional object: a cell phone holder keychain. The main objective was to design a mold with a smooth surface that doesn't show machining marks and use it to cast a quality piece.
1. Mold Design in Fusion 360
The idea started with creating a keychain that could also serve as a phone stand. Using Fusion 360, I sketched and modeled the 3D geometry.
Figure 1: 3D model of the phone holder keychain created in Fusion 360.
I adjusted the base plane to match the real size of the plaster block we had prepared, ensuring there would be no fitting issues during machining.
2. Adjusting Parameters and Heights
A key part of the mold design was using different extrusion heights for different regions. The mold walls were raised higher than the keychain profile:
- To support the silicone mold frame.
- To precisely shape the cast cavity.
- To create a clean base layer with defined edges.
Figure 2: The walls of the mold are taller to support the silicone pour.
3. Machining the Mold
The file was exported for CNC machining. We used a 3-axis milling machine and a ball-nose end mill for smooth finishing on the plaster block.
Figure 3: Machining the plaster block with precision.
After milling, I cleaned the mold carefully with a soft brush and compressed air to prepare it for casting.
4. Silicone Mold Casting
With the mold clean, I prepared and poured silicone into the cavity in thin layers, letting each one partially cure to avoid bubbles.
Figure 4: Pouring silicone to form the final mold.
After a full 12-hour curing process, I carefully demolded the silicone.
5. Producing the Final Piece
I used pigmented epoxy resin to cast the final keychain. A small vibrating motor helped eliminate bubbles during the pour.
Figure 5: Final piece with smooth surface and functional design.
Conclusion
This experience offered a full journey from digital design to physical production. I was able to:
- Design a functional and visually appealing mold.
- Adapt the CAD model to real-world material dimensions.
- Achieve a smooth finish without visible tool marks.
- Successfully replicate the object using silicone and resin.
Planning each step with care and experimenting with materials was key to achieving a professional result. This assignment bridged creativity, precision, and technical skill in a rewarding way.
Week 13: Conclusion
Week 13 was a pivotal stage in our journey through digital fabrication, where we transitioned from abstract design concepts to tangible, functional prototypes. By working with molding and casting processes, we deepened our understanding of material behavior, precision machining, and iterative prototyping.
The group assignment allowed us to collaboratively explore the technical and safety dimensions of plaster, silicone rubber, and epoxy resin. We tested each material’s limitations and advantages, and compared fabrication techniques such as CNC milling versus 3D printing. This comparative approach sharpened our decision-making for future projects.
On an individual level, designing and manufacturing our own molds reinforced our skills in CAD modeling, machine operation, and resin casting. From learning to adjust extrusion heights in Fusion 360, to achieving bubble-free resin pieces, the week highlighted the importance of precision, planning, and patience.
Overall, Week 13 exemplified the interdisciplinary nature of digital fabrication—combining engineering design, craftsmanship, and experimentation. It pushed us to be more autonomous, to document thoroughly, and to reflect on the practicality and aesthetics of our outcomes.
These experiences not only improved our technical proficiency, but also cultivated our ability to approach problems creatively, work as a team, and deliver projects with real-world relevance.
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