Molding and Casting — Group Assignment
Material Testing, Safety Characterization & Process Comparisons
1. Material Safety Data Sheets (MSDS) Review
Before handling materials, our group thoroughly reviewed the safety specs for our lab's casting silicone and polyurethane/epoxy resins.
CRITICAL SAFETY REQUIREMENTS (MSDS Summary):
- Skin/Eye Contact: Resins cause acute dermal irritation and potential sensitization. Nitrile gloves are strictly mandatory (Latex fails against active polymers).
- Inhalation Risks: Isocyanate compounds in curing agents pose respiratory hazards. Mixing must occur in well-ventilated spaces or under localized extraction fume hoods using carbon-filter respirator masks.
- Disposal & Spills: Liquid components are hazardous to aquatic life. Never wash chemical remnants down typical sinks; allow liquid remnants to cross-link and solidify into stable plastic before disposal.
2. Material Performance & Test Cast Comparisons
We mixed test batches of variable casting compounds to analyze cure times, viscosity, and compliance profiles.
| Material Type | Mix Ratio (By Weight/Vol) | Pot Life / Cure Time | Viscosity / Air Bubbles | Flexibility & Properties |
|---|---|---|---|---|
| Flexible Silicone | 1:1 Volumetric | 20 min / 4 hours | High Viscosity (Traps air easily; needs degassing) | Highly elastomeric, ideal for complex shapes. |
| Rigid Casting Resin | 100A:45B Weight | 8 min / 90 minutes | Low Viscosity (Self-degassing but highly exothermic) | Rock hard structure, crisp edge replication. |
3. Process Comparison: Printing vs. Milling Molds
Our lab analyzed workflows for producing positive/negative mold geometries by comparing CNC milling against Sub-Millimeter 3D Printing.
| Metric | CNC Milling (Wax Blocks) | 3D Printing (FDM / SLA) |
|---|---|---|
| Surface Finish | Scalloped finish along toolpaths, dictates precise stepovers (0.1mm) to clean. | Stair-stepping ridges visible; FDM requires extensive sanding/post-glaze steps. |
| Speed & Throughput | Extremely rapid subtraction once paths are set (typically 15-30 mins). | Slow layered generation (Takes several hours depending on height). |
| Design Limitations | Restricted by tool geometry diameter; cannot clear sharp interior inner edges. | High geometry freedom; handles steep overhangs and strict internal corners easily. |
4. Lab Action Gallery
Below is the sequence tracking our safe preparation, proper weighing setups, and chemical curation:
<img src="../assets/media/lab_safety_mix.jpg" alt="Lab scale verification setup">
<img src="../assets/media/test_casts.jpg" alt="Comparative test cast samples">
Group Deliverables Checklist
Completed requirements verification.
- Reviewed MSDS and TDS sheets safely.
- Executed explicit material casting trials.
- Compared additive vs subtractive molding limitations.