What matters
- Calculate required output before choosing cavity count.
- Confirm shot size, projected area, clamp force, platen fit, tie-bar spacing, and cooling capacity on the intended press.
- Balance quality and uptime across cavities, not only the theoretical cycle output.
Begin with required good parts per hour
An eight-cavity mold running a 30-second cycle has a theoretical output of 960 parts per hour. It does not ship 960 good parts every hour after changeovers, maintenance, process checks, rejects, and unplanned stops. Use plant data for utilization when capacity matters.
What changes as cavity count rises
| Potential benefit | New burden to check |
|---|---|
| More parts per cycle | Larger shot, projected area and press |
| Lower machine time per part | Higher mold price and financing exposure |
| Fewer tools for the same volume | One tool can become a larger single point of failure |
| Runner efficiency at scale | Flow and thermal balance across cavities |
| Automated high-volume output | Part handling, inspection and cavity traceability |
A balanced layout is not only symmetrical steel
Runner length, pressure drop, shear history, hot-runner temperature, cooling, venting, gate condition, and cavity dimensions all affect balance. Track process and quality by cavity. A pooled dimension can look acceptable while one cavity trends high and another low.
Compare scenarios over the program
- Annual good-part demand, peak weekly demand, inventory policy, and planned working hours.
- Tool investment, qualification, press rate, expected cycle, labor, runner material, and maintenance.
- Spare capacity, backup tooling, cavity shutoff strategy, and recovery time after failure.
- Volume uncertainty: a modular or lower-cavity start may be worth more than the lowest theoretical unit price.
Use this as a design review, not a production release
These guides support early planning. The selected resin supplier, toolmaker, and molder still need to confirm the final geometry, process window, tolerances, safety factors, validation plan, and commercial assumptions for your application.