Week 14 — Molding and casting
Week 14 follows the official Moulding and Casting module. I used a silicone block mold (negative) taken from a 3D-printed master of a small “sprite” figure for my final project theme, then cast a rigid two-part epoxy copy. The individual assignment is the full mold-and-cast log; the group assignment summarizes our Chaihuo material and safety comparison.
Individual assignment
Off the assignment brief I focused on what I could finish at home: two AB systems (addition-cure silicone for the mold, epoxy “crystal” resin for the part), a disposable cup as a containment shell, and a printed positive I could sacrifice inside the first pour. This matches the nueval FAQ path for a negative mold, as long as the cast releases without destroying the silicone.
1) Task and design choice
My final project circles a set of three spirit-like characters. For Week 14 I wanted one tangible resin replica, both as practice and as a physical prop. I downloaded a suitable sprite-like mesh from a community 3D-printing platform, printed it in PLA as the master, and planned a single-volume pour of silicone around it inside a plastic cup. Splitting the silicone block afterward—rather than building a two-part printed mold—was the compromise that matched my materials and time.
2) Learning (from datasheets, the group page, and trial)
Before mixing anything I read the bottle labels and supplier notes for mix ratios, pot life, and cure time, and I kept the same mindset as in our group assignment: ventilation, gloves, and not rushing the stir. The group comparison already stressed that viscosity and cure profile change bubble behavior; my own extra question was whether uncured silicone would attack the PLA master—I ran a small contact check before committing the full pour (photo below).
3) Plan
- Print master → mount / center in cup → Vaseline as release on the PLA only.
- Weigh silicone A/B, mix, pour, cure (~one day at room temperature).
- Cut a parting path, drill vent ports, demold and clean the cavity.
- Weigh epoxy A/B at the manufacturer ratio, mix until uniform, pour, cure (several days).
- Open silicone and photograph the epoxy cast (“hero shot”).
4) Process log (with photos)
5) Problems, fixes, and how this links to the group write-up
The epoxy photos document the biggest near-miss: under-mixing looks innocent but causes soft spots or sticky regions after cure. I restarted the stir until the streaks disappeared, then accepted some entrained bubbles rather than whipping air in blindly—same “process control beats brand name” lesson as the AB-glue discussion. On the silicone side, cutting a curved parting line took patience but prevented the block from falling into two mismatched slabs.
Compared to the official reminder about smooth mold walls without FDM toolpaths, my mold is silicone (no layer lines), but the cast surface still echoes the FDM master. Next iteration I would sand/fill the PLA or switch the master to a finer process before molding if I need a toy-like finish.
6) Files and checklist (nueval alignment)
- Design file: the printable mesh came from the community platform I used for the master; I can zip the exact STL/3MF here once I mirror it into the repo for permalinking.
- Hero imagery: silicone cavity shots + final epoxy figure (above).
- Group link & reflection: aligned with Chaihuo Week 14 group page on materials and PPE.
- MSDS/TDS: key ratios, cure windows, and ventilation notes are logged from the product sheets that shipped with the four bottles; I will attach PDF links when I mirror them next to the design files.
Group assignment
Guangzhou (Chaihuo) — group documentation: comparing molding and casting materials, safety practices, and process workflows.
For Week 14, we followed the group assignment materials and focused on what we learned from the comparison process: how to read material behavior, how to work safely, and how to choose a process that is realistic for our own project timeline. Instead of treating molding and casting as a single technique, we started to understand it as a workflow that includes material selection, preparation, mixing, curing, and evaluation. That helped us see why even simple casting results can vary a lot depending on small decisions made at the beginning.
Note: The photos below are from the Chaihuo Week 14 group documentation page (shared team material), not individually shot by me in this page. I used them here as visual references to summarize the group observations and to record the main lessons that are most useful for my own future work.
1) Silicone comparison: we learned to choose by behavior, not only by price
The two silicone options (HongDa and ShinBon) taught us that small differences in viscosity and curing profile can strongly affect mold quality, bubble trapping, and demolding convenience. Our key takeaway: always run a small test cast before committing to a final mold. A material that looks cheaper or more convenient at first may actually create more rework if it traps bubbles easily or cures in a way that makes the mold harder to release. This comparison reminded us that material choice should be connected to the shape, detail level, and expected finish of the final part.
2) Safety practice: PPE is part of the process, not optional
The group examples made one point very clear: material handling discipline matters more than speed. Silicone and AB resin can irritate skin/eyes and produce harmful fumes in poor ventilation. We learned to treat PPE, ventilation, and cleanup as mandatory setup steps before mixing. In other words, safety is not something to remember only when a problem appears; it has to be built into the workflow from the start. Preparing gloves, masks, mixing tools, and waste handling in advance also makes the whole process more stable and less stressful.
3) AB glue casting: process control is the main skill
From the AB glue section, we learned that casting quality depends on repeatable process control: consistent ratio, complete mixing, and stable curing conditions. This is directly useful for future composite parts and transparent/rigid cast components. If the ratio is inaccurate or the mixing is rushed, the result can stay sticky, cure unevenly, or contain visible defects. This part of the assignment helped me understand that successful casting is less about one "correct" material and more about building a careful, repeatable method that can be trusted.
4) Personal takeaway for future assignments
For me, the most valuable outcome of this week was not only learning the names of the materials, but also learning how to think before starting. I now have a clearer idea of what questions to ask first: What kind of geometry am I casting? How much detail is needed? Is flexibility or rigidity more important? What failures are most likely, and how can I reduce them before mixing anything? This mindset will be helpful in later assignments and also in my final project if I need custom soft or rigid parts.
- Always do a small pilot cast before final geometry.
- Choose material by viscosity/curing behavior for the target shape.
- Write safety checks into the procedure (PPE, ventilation, disposal).
- Log ratio, timing, and ambient conditions for reproducibility.
Source
Group template and media source: Week 14 — Group Assignment: Molding and Casting.