Injection Mold Cavitation Optimizer: How Many Cavities Minimize Cost per Part
Every added cavity cuts press time per part but raises mold price and needs a bigger press. Somewhere the savings stop. This optimizer sweeps the cavity count and plots machine cost, tooling cost and their sum so you can see the minimum and how flat it is.
Your numbers
The chart sweeps this input from 1 to 32.
Total cycle of the single-cavity case, dominated by cooling time.
Longer fill, pack and plastication as the shot grows. 1 to 3 percent is typical.
Quoted or estimated price for a single-cavity version of the same tool.
Mold cost grows roughly as cavities to the power 0.6 to 0.8 for a family of similar parts.
Fully burdened machine rate for the press sized to a single cavity.
Larger tonnage presses cost more per hour.
Your results
Planning model. Mold cost scaling, cycle penalty and press rates vary by part, steel and shop. Replace the defaults with quotes, and add cost of capital if tool payback matters. Check shot size and clamp tonnage before choosing a cavity count.
Cost per part vs number of cavities
Sweeps Cavities to evaluate from 1 to 32, holding your other inputs fixed.
Quote history based cavitation advice
Optional: see how your past mold quotes and actual cycle times could calibrate this model automatically.
Optional. The tool and every export work without this. No spam.
How to use it
Start with your annual volume and program length, then enter the cycle time and mold quote for a single cavity. Set the scaling exponent and cycle penalty from your tool shop's quotes at two cavity counts, or leave the defaults. Read the chart: the total curve usually drops steeply, flattens, then rises slightly as mold cost and press rate catch up. Pick the lowest point, then move left if volume is uncertain, because fewer cavities hedge the risk of a program that ends early.
The model
Output rate is cavities times 3600 divided by cycle seconds, times efficiency. Cycle grows by a small percentage with every added cavity. Mold cost is the single-cavity price times cavities to the power of the exponent, a common rule of thumb for similar part families. Machine cost per part is the hourly rate, scaled for larger presses, divided by good parts per hour. Tooling cost per part is mold cost spread over lifetime volume. The cavity count with the lowest sum is the cost optimum.
- Parts per hour = cavities x 3600 / cycle x efficiency
- Mold cost = single-cavity cost x cavities^exponent
- Tooling per part = mold cost / (annual volume x years)
Reading the result
At 600,000 parts a year over 5 years the default case lands in the low double digits, with the curve nearly flat across 8 to 16 cavities. That flatness is the useful finding: when two cavity counts are within a few percent, choose the one with lower tool risk, a smaller press and shorter lead time. Raise volume and the optimum moves right. Cut program life or add cost of capital and it moves left.
Limits and checks
The cost model ignores physical limits. A high cavity count may not fit the platen, may exceed shot capacity, may not balance the runner, or may force a hot runner you did not budget. Part quality also drops when cavity-to-cavity variation grows. Confirm clamp and shot with a tonnage check and get a real quote for the final choice.
- Compare press hours per year with available hours
- Confirm shot size is 20 to 80 percent of barrel capacity
- Ask for quotes at two cavity counts to calibrate the exponent
Frequently Asked Questions
Is a mold with twice the cavities twice the price?
No. Shared base, runner system and mold setup mean cost typically rises with cavities to a power between 0.6 and 0.8, so doubling cavities adds roughly 50 to 75 percent. Your tool shop's quotes at two cavity counts give the real exponent for your part.
Why does the cycle time increase with more cavities?
Cooling time depends on wall thickness and does not change, but a larger shot takes longer to plasticize, fill and pack, and bigger molds open and close more slowly. The penalty is small, usually 1 to 3 percent per added cavity.
Does the optimizer include resin cost?
No. Resin per part is the same at every cavity count except for runner size, so it does not change the optimum for a given design. Use the resin impact and part cost tools for a full cost view.
What if volume is uncertain?
Run the optimizer at low, expected and high volume. If the best cavity counts differ, choose the lower one, or consider a family or modular mold that can add cavities later if volume proves out.
If your cycle times, press rates and mold costs sit in an ERP and MES, Netray can build an agent that evaluates cavitation scenarios for new quotes from your own history.
Related Tools
Injection Molding Press Selection Worksheet (Tonnage and Shot Utilization)
List each mold with projected area, cavities, cavity pressure and the press you plan to use. The sheet computes required tonnage, clamp utilization and shot utilization for every row.
Engineering & PLMAPQP Tooling Cavity Count Calculator
Size the number of cavities per tool from annual demand, peak factor, cycle time, OEE and available hours before you commit to a tooling quote.
Costing & FinanceHot Runner vs Cold Runner Payback Calculator
Work out whether the extra cost of a hot runner system pays back through saved resin and shorter cycles, with a sweep over annual shot volume.
Industry TemplatesInjection Molding Cycle Time Calculator
Estimate cooling time from wall thickness and temperatures, then total cycle time, parts per hour and output per shift.
Costing & FinanceTooling and NRE Amortization Per Piece Calculator
Amortize tooling and NRE over lifetime volume, add financing, and see the effect on piece price at different volumes.
More Engineering & PLM tools
See all- Mold Steel Grades Selection Reference
- Injection Mold Gate Types Reference
- Mold Cooling Channel Reynolds Number, Flow and Heat Removal Calculator
- SAP Super BOM Design Worksheet
- SAP Engineering Change Number Checklist
- SAP Document Info Record Template
- SAP Change Master and Revision Level Log
- SAP Engineering Change Request (ECR) Template
- SAP BOM Usage and Item Category Reference
Keep exploring
Free tools
- Injection Mold Maintenance ChecklistA practical preventive maintenance checklist for injection molds, from daily checks at the press to full overhaul and storage.
- Injection Mold Gate Types ReferenceA comparison table of common mold gate types with where each works best, trade-offs and how the gate is removed.
- Mold Changeover Time Log WorksheetLog each mold change by phase, total the minutes and see which jobs miss your changeover target.
Guides
- Injection Molding Production Scheduling: Matching Molds, Presses and ResinHow to schedule injection molding: match molds to presses by tonnage and shot size, plan changeovers and resin drying, and keep capacity honest with real cycle data.
- How to Estimate Injection Mold Tooling CostA practical method to estimate injection mold cost: SPI class, cavitation, steel, hot runner, slides and lifters, texture, and how molders quote tooling.
- Best ERP for Injection Molders: What to Check Before You BuyWhat to look for in ERP for injection molders: mold and press tracking, resin lots, MES integration, scrap and regrind, and how DELMIAworks, Plex and Epicor compare.
AI on your ERP
- Epicor Kinetic AI for Injection Molders: Resin, Tooling, Scrap and Cycle Time Questions AnsweredPrivate AI on Epicor Kinetic for injection molders: query resin lots, tooling, scrap and cycle-time variance in plain English, with the query shown.
- AI on Infor SyteLine for Plastics Injection Molders: Presses, Molds, Resin and ScrapAI on Infor SyteLine for injection molders: mold and press scheduling, resin and regrind lots, scrap and cycle variance, on-prem and read-only by default.
Manufacturing hubs
- Ningbo and Yuyao, Zhejiang: Molds, Plastics and Hardware ManufacturingGuide to Ningbo and Yuyao manufacturing: mold making, injection molding and hardware, the port, typical ERP and quoting problems, and where private AI helps.
- Plastics Industry Association (PLASTICS): Molders, Processors and ERP RealitiesHow injection molders and plastics processors work in the PLASTICS ecosystem: NPE, safety standards, quoting, ERP and MES, and private AI on shop data.