Key Factors Affecting the Number of Cavities in Injection Molds

1. Injection Machine Capability

• Clamping Force (Tonage) – More cavities increase the projected mold area, requiring higher clamping force to prevent flash. Insufficient force may limit cavity count.

• Shot Capacity – Multi-cavity molds consume more plastic, so the machine must provide enough melt volume (including runners).

• Platen Size – The mold must fit within the machine’s maximum mold space; oversized multi-cavity molds may be unfeasible.

2. Production Requirements

• Order Volume – High-volume production favors multi-cavity molds for efficiency, while prototypes or small batches may use fewer cavities.

• Cycle Time – More cavities can reduce per-part cycle time, but cooling and ejection complexity must be balanced.

3. Mold Cost & Complexity

• Manufacturing Cost – Multi-cavity molds cost more (machining, cooling, ejection systems), but per-part cost decreases.

• Maintenance Risk – If one cavity fails, the entire mold may need downtime, affecting production stability.

4. Part Size & Design

• Large Parts (e.g., automotive panels) often use fewer cavities due to space constraints.

• Complex Geometry may require specialized gating or ejection, limiting cavity count.

5. Runner & Gating System

• Flow Balance – Multi-cavity molds need balanced runners (H-type, radial) to ensure uniform filling.

• Cold Runner vs. Hot Runner –

• Cold runners take up space, restricting cavity count.

• Hot runners save material and allow more cavities but increase cost.

6. Cooling Efficiency

• Uneven cooling in multi-cavity molds can cause warpage or longer cycle times.

7. Material Properties

• Low-fluidity materials (e.g., PC) may require larger gates or fewer cavities for proper filling.

8. Quality Control

• High-precision parts (e.g., medical components) may use fewer cavities to minimize variation.

Real-World Examples

Conclusion

Choosing the right number of cavities involves balancing machine capacity, cost, efficiency, and quality. Moldflow analysis can help validate flow balance before manufacturing. For mass production, multi-cavity molds maximize output, while complex or high-value parts may prioritize precision over cavity count.