What Is Vacuum Casting?
Vacuum casting is an advanced low-volume manufacturing technique combining silicone mold flexibility with vacuum-assisted resin infusion. Unlike injection molding, it’s ideal for producing 10–50 identical parts with production-grade material properties (e.g., ABS-like, transparent, or rubber-like polyurethanes).
Key Characteristics:
- Resolution: Captures details down to 0.05mm (comparable to injection molding).
- Materials: 500+ Shore hardness options (from soft elastomers to rigid plastics).
- Industry Standards: Complies with ISO 9001 for controlled environments.
How Does Vacuum Casting Work? (Step-by-Step)
1. Master Model Preparation
- Input: 3D-printed (SLA/DLP) or CNC-machined master, often post-processed with sanding/polishing.
- Critical Detail: Surface finish directly transfers to final parts – any defects will replicate.
2. Silicone Mold Fabrication
- Process: Liquid silicone (e.g., Dragon Skin®) is poured over the master in a pressure pot (1–2 bar) to prevent microbubbles.
- Curing: 4–8 hours at 40°C for optimal tear resistance.
- Mold Design: Requires venting channels and sprue gates for resin flow.
3. Vacuum Casting Cycle
- Degassing: Resin mixed with catalyst is vacuumed (-0.95 bar) for 3–5 minutes to eliminate air.
- Pouring: Resin injected into mold under vacuum to prevent void formation.
- Curing: 60–80°C oven for 1–4 hours (depends on resin system).
4. Post-Processing
- Demolding: Silicone molds allow undercuts but require careful cutting.
- Finishing: Parts may need UV coating, dyeing, or assembly (for multi-material casts).
Advantages and Disadvantages of Vacuum Casting
✅ Advantages
- Economic Efficiency
- Tooling cost: $200–$500/mold vs. $5k+ for injection molds.
- Break-even point: ~50 parts (vs. 1,000+ for injection molding).
- Material Performance
- Tensile strength: Up to 60 MPa (comparable to ABS).
- Thermal resistance: Some resins withstand 100–120°C (e.g., RenCast® 640).
- Design Flexibility
- Overmolding: Embed inserts (metals, electronics) in a single step.
- Transparency: Optical-grade resins like ClearFlex® for lenses.
❌ Disadvantages
- Mold Limitations
- Max 50 cycles before silicone loses dimensional stability.
- Not suitable for glass-filled or high-impact materials.
- Geometric Constraints
- Wall thickness: 1–5mm (thicker sections risk sink marks).
- Undercuts require mold segmentation, increasing cost.
- Labor Intensity
- Manual processes (e.g., degassing, demolding) limit scalability.
Applications by Industry
🚗 Automotive
- Functional prototypes: HVAC components, dashboards (tested for vibration/heat).
- Pre-production: Mirror housings in ABS-like resin (validated for fitment).
🏥 Medical
- Biocompatible devices: Hearing aid shells (ISO 10993-certified resins).
- Ergonomic testing: Handheld surgical tools with soft-grip overmolding.
🎮 Consumer Electronics
- Cosmetic prototypes: Smartphone cases in matte/flexible finishes.
- Waterproof testing: Wearable device housings (simulating IP67 seals).