The main difference between injection molding and vacuum casting(also known as urethane casting) is that injection molding is designed for high-volume production using durable metal molds, while vacuum casting is ideal for low-volume runs using flexible silicone molds.
Injection molding involves injecting molten thermoplastic into precision-machined steel or aluminum molds, delivering tight tolerances and excellent surface finishes. It requires a high upfront tooling investment but offers extremely low per-part costs at scale.
In contrast, vacuum casting uses polyurethane resins poured into silicone molds under vacuum. It’s much faster and cheaper to start but less durable, with limited mold life and lower dimensional accuracy.
Key Difference Between Injection Molding and Vacuum Casting
| Factor | Injection Molding | Vacuum Casting |
|---|---|---|
| Process | High-pressure injection into metal molds | Low-pressure resin casting in silicone molds |
| Mold Cost | 10,000+ (steel/aluminum mold) | (silicone mold) |
| Lead Time | 3-8 weeks (tooling) | 3-7 days |
| Production Volume | 1,000+ parts (up to millions) | 1-500 parts |
| Materials | Engineering thermoplastics (ABS, PC…) | Polyurethane resins |
| Part Accuracy | ±0.1mm tolerance | ±0.3mm tolerance |
| Surface Finish | Excellent, consistent | Good (may require post-processing) |
| Best For | Mass production, end-use parts | Prototypes, bridge tooling |
When to Choose Which:
Injection Molding when:
• Producing >500 parts
• Needing production-grade materials
• Requiring tight tolerances
• Budget allows for high tooling costs
Vacuum Casting when:
• Need <100 prototypes fast
• Testing multiple design iterations
• Limited budget for tooling
• Short-run production of non-structural parts
Technical Note: Vacuum casting parts typically have 70-80% the strength of injection molded counterparts, making them unsuitable for most functional end-use applications. The process excels in design validation and low-volume production where injection molding tooling costs would be prohibitive.
