14. Mold and Casting
For this week, I designed an Innovation Department badge in Fusion 360, exported it as an STL file, and 3D-printed the master pattern for molding and casting.
Group assignment page: Chaihuo Lab Week 14 Group Assignment
Self Reflection (Based on Group Work)
During the molding and casting group assignment, I learned that material choice is not only about casting quality, but also about safety, handling workflow, and repeatability. By reviewing the SDS sheets and comparing HongDa and ShinBon silicone in real tests, I could see that small differences in viscosity and curing behavior directly affect mold detail and bubble formation. This helped me understand why test casts are necessary before committing to a final mold.
Working with AB glue also made me more aware of responsible lab practice. The two-part resin system is effective, but it has higher risks such as skin and eye irritation, harmful fumes, and potential chemical burns if handled carelessly. Through this process, I developed a stronger habit of preparing PPE first, checking ventilation before mixing, and planning disposal in advance. My key takeaway is that good fabrication is inseparable from good safety discipline: consistent protection and careful procedure lead to both better results and a safer team workflow.
Workflow and Notes
I started by designing the badge in Fusion 360 and 3D-printing the master pattern.
Step 1: Design the badge outline in Fusion 360.
Step 2: Extrude the outline to the target thickness.
Step 3: Use the offset tool to create the inner and outer badge edges.
Step 4: Extrude the edge profiles to the required thickness.
Step 5: Add the text using the Text tool.
Step 6: Use a conic curve to define the path used to align the text.
Step 7: Build the bottom base and add the Innovation Department logo.
Step 8: Apply fillets to sharp corners, including text edges and box corners.
I printed the badge master with a 0.4 mm nozzle because a 0.2 mm nozzle was not available. The printed surface shows visible layer lines. I was concerned that these lines might affect molding and casting quality. In practice, they can transfer to the mold surface, so post-processing (such as light sanding or primer) is helpful when a smoother final cast is required.
For silicone use, I followed the label instructions: mix silicone and curing agent at a 100:2 ratio, stir thoroughly, and complete the operation within about 5 minutes. After pouring into the mold box, wait until fully cured before demolding. I also learned that testing a small batch first is very useful for understanding curing speed and avoiding material waste.
Bubble Reduction Methods
- Use a slightly lower curing-agent ratio to extend curing time, allowing more bubbles to escape naturally.
- Stir in one consistent direction to reduce additional air entrainment.
- Brush a thin first layer of silicone onto the master, wait for bubbles to disappear, then pour the rest.
- Use a vacuum machine after mixing to degas the silicone.
Material reference: Dongguan Lixing Technology Co., Ltd. (shelf life: 6 months).
Problem and Fix
In my first attempt, I forgot to add the curing agent. Even after 24 hours, the silicone was still liquid.
I have not completed the second trial yet. In the next attempt, I will remake the batch using the correct 100:2 ratio and mix thoroughly before pouring. The key lesson is to prepare a clear pre-pour checklist and verify each step before mixing, because I can become careless when rushing. I will also do a small test batch first to confirm curing before pouring the full mold.
Student's checklist – 0 / 7
- ☐ Linked to the group assignment page and reflected on what you learned on your individual page
- ☐ Reviewed the SDS for each molding and casting material, then made and compared test casts
- ☐ Documented how you designed and made your 3D mold, including machine settings
- ☐ Ensured the mold has a smooth surface finish with no visible production marks
- ☐ Documented how you safely made the mold and cast the parts
- ☐ Described the problems you encountered and how you fixed them
- ☐ Included your design files and a hero shot of the mold and final object