WEEK 14 - Molding and Casting
Group Assignment
Introduction
The group assignment for Week 14 focused on understanding the complete molding and casting workflow from a material, safety, and process perspective. As a team, we analyzed different molding and casting materials, reviewed their Safety Data Sheets (SDS), and identified the correct handling procedures, personal protective equipment, curing conditions, and possible risks associated with each material.
This group work was important because molding and casting processes involve chemical materials that require controlled preparation, accurate mixing, proper ventilation, and safe demolding practices. By reviewing the SDS information, we were able to understand the potential hazards, recommended storage conditions, protection requirements, and emergency procedures before using the materials in the lab.
During the group assignment, we also evaluated the behavior of different materials during mixing, pouring, curing, and demolding. We observed aspects such as viscosity, curing time, flexibility, surface finish, dimensional stability, and ease of release from the mold. These observations helped us compare the suitability of each material for different digital fabrication applications.
The knowledge gained from the group assignment was directly applied to my individual work. Understanding the material behavior and safety requirements helped me plan the fabrication of my CNC-machined master mold, the silicone molding process, and the final epoxy resin casting with better control and fewer risks.
Individual Assignment: CNC Mold, Silicone Mold and Resin Casting
The objective of the individual assignment was to design and fabricate a mold using a digital fabrication process, produce a flexible mold from it, and finally cast a physical object. For this assignment, I developed a cat face mold based on a digital model downloaded from Printables. The original model was used as a starting reference and was later adapted to create a manufacturable mold for the molding and casting process.
The digital preparation of the model was carried out in Autodesk Fusion 360. In this stage, the cat face geometry was reviewed, positioned, and integrated into a rectangular mold block. The mold design included enough border, wall thickness, and depth to contain the silicone material during pouring and to allow the final shape to be reproduced correctly during casting.
After preparing the 3D model, the CAM process was developed in Aspire. In this software, I defined the stock dimensions, material thickness, machining origin, cutting strategy, and toolpath preview. The G-code was generated in Aspire and later used to machine the positive master mold on a CNC Router using a 6 mm milling bit.
Once the CNC machining process was completed, the mold surface showed visible toolpath marks, especially in the curved areas of the cat relief. To improve the quality of the final casting, I manually sanded the surface and sealed the mold. This post-processing step was necessary to reduce porosity, improve surface finish, and help the silicone release more easily from the CNC-machined master.
After the master mold was prepared, I mixed and poured the silicone material into the CNC-machined mold. The silicone was poured slowly from one side to reduce trapped air and improve the reproduction of the details. Once cured, the flexible silicone mold was demolded and used as the negative mold for the final casting stage.
For the final object, I used EPOX-21 epoxy resin. The two resin components were measured, mixed slowly, and poured into the silicone mold. The cast was left to cure for 72 hours before demolding to ensure complete polymerization and dimensional stability. The final result successfully reproduced the cat face geometry and demonstrated the complete workflow from digital design to CNC machining, silicone molding, and resin casting.
1. Individual Workflow
- Reviewed the group assignment results, including material behavior, SDS information, and safety recommendations.
- Selected the cat face model from Printables as the base geometry for the individual mold.
- Prepared and adapted the 3D model in Fusion 360 to create a positive master mold.
- Added a rectangular mold frame with enough border, depth, and wall thickness to contain the silicone.
- Prepared the CAM process in Aspire by defining stock size, origin, toolpath strategy, and machining parameters.
- Generated the G-code in Aspire for CNC Router machining.
- Machined the mold using a CNC Router and a 6 mm milling bit.
- Inspected the machined surface and identified visible toolpath marks.
- Sanded the mold manually to improve the surface finish.
- Sealed the mold to reduce porosity and improve silicone release.
- Prepared and mixed the silicone material following the safety recommendations.
- Poured the silicone slowly into the CNC-machined master mold.
- Allowed the silicone to cure and carefully demolded the flexible mold.
- Prepared and mixed the EPOX-21 epoxy resin.
- Poured the resin into the silicone mold and allowed it to cure for 72 hours.
- Demolded the final resin piece and documented the complete process.
2. Cat Design and Digital Preparation for CNC Machining
The individual mold was developed from a kitten face relief model. The original geometry was downloaded from Printables as a reference model: Cat Face model. After downloading the file, I imported and prepared it in Autodesk Fusion 360.
First, I reviewed the geometry of the cat face and inspected the mesh to understand the relief details and the overall shape of the model. Then, I positioned the relief on a rectangular base to create a machinable master. After that, I added external walls around the geometry to define the mold limits and to create a containment area for the silicone.
These design modifications were necessary because the original downloadable file was only a decorative relief, while the assignment required a functional mold master suitable for CNC machining. The final design included the cat face relief, a solid base, and surrounding walls that would later help contain the silicone during the molding process.
Once the 3D model was completed in Fusion 360, the geometry was exported and prepared in Aspire for the CAM process and G-code generation. This file was then used to machine the mold on the CNC Router with a 6 mm milling bit.
| Design Step | Description |
|---|---|
| Original model reference | The kitten face model was downloaded from Printables: Cat Face model. |
| Software used | Autodesk Fusion 360 was used for the 3D design preparation. Aspire was used for the CAM process and G-code generation. |
| Initial geometry review | The original model was inspected in shaded and mesh views to verify the relief details and general shape. |
| Base creation | The cat relief was positioned on a rectangular solid base to create a machinable master. |
| Containment walls | Walls were added around the relief to define the mold limits and create a containment area for the silicone. |
| Final purpose | The final Fusion 360 model was prepared as a positive CNC master for silicone molding and final epoxy resin casting. |
Design Evidence in Fusion 360
The following screenshots document the digital preparation process of the kitten mold in Fusion 360. They show the imported relief, the mesh inspection, the placement of the geometry on a rectangular base, and the addition of the external walls required to create the final mold master.
Design Files Used for the Kitten Mold
The downloaded cat face model was used as the starting geometry. From this model, I generated my own Fusion 360 design file and adapted the geometry for the molding and casting workflow by adding the base, walls, and silicone containment area. After preparing the 3D geometry, the machining file was processed in Aspire to create the CNC Router toolpaths and export the G-code. This modification was necessary because the original model was a decorative relief, while my assignment required a manufacturable mold master for CNC machining.
| File | Use in the Assignment |
|---|---|
| Cat Face model from Printables | Original kitten relief used as the starting 3D geometry. |
| Mecanizado gato.f3d | Fusion 360 file used to prepare the mold block, base, walls, and kitten relief before exporting the geometry for CAM. |
| Aspire CAM / G-code file | File used to generate the CNC Router machining paths using a 6 mm milling bit. |
3. CAM Process and Milling Strategy
After finishing the digital design in Fusion 360, I used Aspire to prepare the CAM operations and generate the G-code for the CNC Router. In Aspire, I defined the stock dimensions, the material thickness, the machining origin, and the position of the cat relief inside the rectangular mold block. The top surface of the material was used as the Z reference plane, and the toolpaths were previewed before machining to verify that the cutter could reach the main areas of the kitten relief.
The machining process was planned according to the geometry of the relief and the available tool. A 6 mm milling bit was used to machine the mold on the CNC Router. The strategy removed the material progressively and created the cavity, border, and kitten face relief. Because the tool diameter limits the level of detail that can be reproduced directly by machining, sanding and sealing were later used to improve the final surface before pouring silicone.
| CAM Item | Documentation |
|---|---|
| CAM software | Aspire was used to create the toolpaths and export the G-code for the CNC Router. |
| Setup | Stock, material thickness, origin, and Z reference were defined in Aspire before generating the toolpaths. |
| Roughing strategy | Material was removed progressively using a 6 mm milling bit on the CNC Router. This operation created the main cavity and mold border. |
| Finishing strategy | The 6 mm tool followed the relief geometry as much as possible. The remaining surface marks were corrected manually by sanding. |
| Toolpath verification | The Aspire preview was checked before exporting the G-code to verify machining depth, remaining stock, and possible collisions. |
| Manufacturing objective | Produce a positive master with enough surface quality to later make a silicone mold. |
4. CNC Milling Process
The cat mold was fabricated using a CNC Router. The machine followed the G-code generated in Aspire and removed material layer by layer until the face, ears, eyes, nose, whiskers, and surrounding cavity were created. The 6 mm milling bit generated the main shape of the mold and left visible machining marks on some curved areas of the relief.
The cutting tool used for the process was a 6 mm milling bit. This tool was suitable for removing material and producing the general relief of the kitten mold. However, because the geometry included small decorative details, some areas could not be perfectly smoothed only with the CNC Router. After machining, visible toolpath marks remained on the surface, especially in curved areas, so a sanding and sealing process was required before pouring the silicone.
| Machining Element | Purpose in the Process |
|---|---|
| 6 mm milling bit | Used on the CNC Router to remove material and machine the kitten mold relief. |
| Aspire G-code | Used to control the CNC Router machining path for the cat mold. |
| CNC Router machining | Produced the positive master that was later used to create the silicone mold. |
| Post-processing | Sanding and sealing were applied to reduce toolpath marks and improve the mold release. |
5. Sanding and Surface Correction
After milling, the mold was corrected by sanding. This step was necessary to reduce the toolpath marks and obtain a smoother surface finish. The goal was to prevent the production process from being visible in the final cast.
6. Mold Sealing
The milled mold was sealed before pouring silicone. Sealing reduced the porosity of the wood-based material, improved the surface finish, and helped the silicone release more easily after curing.
7. Silicone Preparation
Safety equipment was used during the process, including gloves, safety glasses and a mask. The silicone material was mixed carefully to obtain a homogeneous mixture and avoid uncured areas.
8. Pouring Silicone into the CNC Mold
The silicone mixture was poured slowly into the CNC-machined mold. Pouring from one side allowed the material to flow naturally across the surface and helped reduce trapped air in the detailed areas of the cat face.
9. Silicone Mold Demolding
After curing, the silicone mold was carefully removed from the CNC master. The flexible mold captured the cat face details and was ready to be used for resin casting.
10. EPOX-21 Resin Preparation
For the final casting stage I used EPOX-21 epoxy resin. The material included component A and component B. The resin was mixed slowly to avoid bubbles and to obtain a uniform mixture before pouring it into the silicone mold.
Technical Sheet: EPOX-21 Resin Preparation
Before casting, I prepared a technical sheet to organize the material information, safety requirements, and practical parameters used during the resin preparation. This helped me work more carefully with the two-component resin system and avoid common casting problems such as bubbles, incomplete curing, or premature demolding.
| Technical Item | EPOX-21 Resin Preparation |
|---|---|
| Material type | Two-component clear epoxy casting resin: component A / base resin and component B / curing agent. |
| Application in this assignment | Final resin casting inside the flexible silicone mold produced from the CNC-machined cat face master. |
| Mixing ratio | 4 parts of component A + 1 part of component B, according to the DURA QUARZ epoxy resin technical sheet. Both components must be measured carefully before mixing. |
| Mixing method | Measure each component separately, combine them in a clean mixing container, and mix slowly for at least 3 minutes. A slow movement helps reduce trapped air and visible bubbles. |
| Working time | Approximately 1 hour at 77°F / 25°C, depending on room temperature and resin volume. |
| Curing time used | 72 hours before demolding. I selected the longer curing time to avoid deforming the final piece and to ensure better dimensional stability. |
| Recommended pour behavior | Pour slowly into the silicone mold, starting from one area and allowing the resin to flow into the details. This reduces bubbles in fine features. |
| Safety equipment | Nitrile or rubber gloves, safety glasses, long sleeves, and good ventilation. Direct skin contact and breathing fumes should be avoided. |
| Storage | Keep containers tightly closed, away from direct sunlight and heat, and store under 25°C when possible. |
| Quality controls | Check that the mixture is uniform, inspect for bubbles before pouring, keep the mold level, and do not move the casting during curing. |
| Reference | Open DURA QUARZ Epoxy Resin Technical Sheet |
Visible Technical Sheet: DURA QUARZ Epoxy Resin
The technical sheet of the epoxy resin used in this assignment is shown below. This document was used to verify the material description, mixing ratio, curing time, safety precautions, and application recommendations before preparing the final resin casting.
11. Resin Casting into the Silicone Mold
Once the resin was mixed, it was poured into the silicone mold. The resin was added slowly so that it could fill the detailed areas of the mold and reduce the formation of bubbles.
12. Hero Shot – Final Resin Casting Result
This hero shot presents the complete result of the molding and casting workflow developed during this assignment. Starting from a digitally prepared cat relief, a CNC-machined master mold was fabricated using a CNC Router and later improved through sanding and sealing to reduce visible toolpath marks. A flexible silicone mold was then produced from the CNC master and used to cast the final piece using EPOX-21 epoxy resin.
The resin was mixed according to the manufacturer's specifications and poured carefully into the silicone mold. To ensure complete polymerization and dimensional stability, the cast remained undisturbed for 72 hours before demolding. The final result successfully reproduced the geometry and details of the original design while achieving a smooth surface finish and good structural integrity.
This outcome validates the complete workflow of digital design, subtractive manufacturing, mold preparation, silicone molding, resin casting, and final demolding. The project demonstrates how CNC machining and casting techniques can be combined to create accurate and repeatable parts with high-quality surface finishes.
13. Problems and Solutions
| Problem | Solution |
|---|---|
| Visible tool marks after CNC milling | The mold was sanded manually to improve the surface finish before making the silicone mold. |
| Limited detail due to the 6 mm milling bit | The mold was designed with manufacturable relief features, and the surface was manually corrected after machining. |
| Porosity of the milled material | The mold was sealed before pouring silicone to improve release and reduce surface defects. |
| Risk of bubbles in silicone and resin | The materials were mixed slowly and poured carefully from one side of the mold. |
| Risk of premature demolding | The resin was left to cure for 72 hours before demolding. |
14. Download Files
The original kitten relief reference was downloaded from Printables and later modified in Fusion 360 for the molding and casting assignment. The final Fusion 360 file documents the adapted mold design used for CNC Router machining.
15. Fab Academy Checklist
- Linked to the group assignment page and reflected on my individual page what I learned
- Reviewed the safety data sheets for each molding and casting material
- Documented how I designed and created my 3D mold, including Fusion 360 preparation, Aspire CAM setup, CNC Router machining and the 6 mm milling bit
- Ensured the mold has a smooth surface finish through sanding and sealing
- Shown how I safely made the mold and cast the parts
- Described problems and how I fixed them
- Included design files and hero shot of the mold and final object
16. Final Reflection
This assignment allowed me to understand how molding and casting connects digital design, subtractive manufacturing, material preparation, and final part production. Through the group assignment, I learned the importance of reviewing Safety Data Sheets, selecting appropriate materials, and following safe working procedures when using silicone and epoxy resin systems.
In the individual assignment, I applied this knowledge by designing and manufacturing a cat face mold. I prepared the model in Fusion 360, generated the G-code in Aspire, machined the master mold on a CNC Router using a 6 mm milling bit, improved the surface through sanding and sealing, produced a silicone mold, and finally cast the piece using EPOX-21 epoxy resin.
One of the most important lessons was that the quality of the final casting depends on every previous step. The digital model must be designed according to the manufacturing process, the CAM strategy must consider the tool diameter and machining limitations, and the mold surface must be corrected before casting. I also learned that slow mixing, careful pouring, and sufficient curing time are essential to reduce bubbles, avoid defects, and obtain a clean final part.
Overall, this week helped me understand the complete molding and casting workflow and how it can be used to create repeatable parts from a digitally fabricated master mold. The final resin cat face confirmed that the process was successful and that CNC machining, silicone molding, and epoxy casting can be combined effectively to produce detailed physical objects.