Injection Molding Cycle Time Calculator
Cycle time drives part cost more than almost any other molding variable, and cooling is usually the largest slice. This calculator estimates cooling from wall thickness and temperatures, then builds up to cycle time, parts per hour and shift output.
Your numbers
Roughly 0.07 to 0.10 for ABS, PC and PS, about 0.10 to 0.15 for PP and PE.
Average part temperature at which it is stiff enough to eject.
Your results
The cooling formula is a one-dimensional estimate for a flat section. Real cooling depends on channel layout, coolant temperature, material and part geometry.
Cycle time (s) vs wall thickness
Sweeps Maximum wall thickness from 1 to 6, holding your other inputs fixed.
Compare routing cycle times with real press data
Optional: a short review of how to feed actual cycle times from your presses back into ERP routings.
Optional. The tool and every export work without this. No spam.
How to use it
Enter the thickest wall that governs cooling, the resin's thermal diffusivity, and the three temperatures: melt, mold wall and ejection. Add fill time, hold time and the dry cycle (mold open, eject and close). Enter cavity count and a realistic efficiency for the job. The tool returns cooling time, total cycle, parts per hour and an eight hour output. Use it during quoting, then compare against actual press data once the job runs.
- Use the thickest wall that is not a rib or boss.
- Ejection temperature is the part average, not the surface.
- Check the dry cycle against the press datasheet.
The method
The estimate uses the classic one-dimensional heat conduction result for a slab: cooling time equals wall thickness squared, divided by pi squared times thermal diffusivity, times the natural log of four over pi times the ratio of melt minus mold temperature to eject minus mold temperature. Cooling grows with the square of thickness, so a 3 mm wall takes about 1.44 times as long as a 2.5 mm wall. Hold time overlaps cooling, so the cycle takes the larger of the two after fill.
Worked example and reading results
With the defaults (2.5 mm ABS-like wall, 230 C melt, 60 C mold, 90 C eject) cooling comes out near 14 seconds, giving a cycle of roughly 20 seconds. Four cavities then make about 700 parts per hour, or about 4,800 good parts per shift at 85 percent efficiency. If measured cooling on the press is far longer, look at coolant temperature, flow rate, channel distance to the cavity and hot spots rather than just adding time.
Common mistakes
Using nominal wall rather than the thickest section understates cooling. Setting the mold temperature to the chiller setpoint instead of the actual wall temperature hides poor channel design. Counting hold and cooling as additive double counts time. Finally, remember that plasticizing time can become the limit on large shots with slow screw recovery, so compare recovery time to the cooling time before trusting the result.
Frequently Asked Questions
How is injection molding cooling time calculated?
A common estimate is wall thickness squared divided by pi squared times thermal diffusivity, multiplied by the natural log of the temperature ratio between melt, mold and ejection temperature. It is a one-dimensional approximation for a flat wall.
What share of the cycle is cooling?
For many parts cooling is 50 to 80 percent of the total cycle, rising with wall thickness. Thin-walled packaging is closer to fast fill and short cooling, while thick technical parts are dominated by cooling.
How do I reduce cycle time?
Look at cooling first: colder coolant, turbulent flow, conformal or closer channels, thinner walls and a higher allowable ejection temperature. Then trim hold time using a gate-seal study and tighten the dry cycle.
Why is my real cycle longer than the estimate?
The estimate ignores robot or degating time, slow ejection, screw recovery, thick ribs and bosses, and cooling circuit inefficiency. Compare each element against a timed cycle breakdown on the press.
If your ERP routings still carry guessed cycle times, we can help compare them with real press data. Reach out for a short review.
Related Tools
Injection Molding Clamp Tonnage Calculator
Estimate the clamp force a mold needs from projected area, cavity count and average cavity pressure, and see which press size fits.
Industry TemplatesInjection Molding Shot Weight and Shot Size Calculator
Calculate total shot weight from part and runner volume, then check it against the barrel capacity and melt residence time.
Costing & FinanceInjection Molded Plastic Part Cost Calculator
Build up the cost per good molded part from material, machine time, labor, scrap, secondary operations and tool amortization.
Industry TemplatesResin Drying Time and Temperature Reference
Typical drying temperature, time and maximum moisture for common injection molding resins, in a table you can search and export.
More Industry Templates tools
See all- Injection Molding Process Sheet Template
- Distributor Free Freight Policy Template
- Job Shop Quote Cover Letter Template
- Monthly Operations Review Meeting Pack Template
- OEE Improvement A3 Charter Template
- Sheet Metal Job Traveler Template
- Press Brake Setup Sheet Template
- Sheet Metal Cut List and Material Takeoff Worksheet
- Welding Wire Deposition Rate Calculator
Keep exploring
Free tools
- Injection Molding Cooling Time CalculatorEstimate the cooling time of a molded part from wall thickness, resin thermal diffusivity, melt, mold and ejection temperatures, and see how it drives total cycle time.
- Molding Scrap and Cycle Time SQL Query GeneratorGenerate generic SQL for molding scrap rate by tool and press, cycle time against standard, and mold shot-count maintenance alerts.
- Injection Molding Process Sheet TemplateA fill-in setup sheet that records the validated process window for a mold, press and resin, ready to print or export.
Guides
- Injection Molding Job Costing: Finding Where Quoted Margin DisappearsHow injection molders find margin leaks: compare quoted and actual cycle, scrap, resin and downtime by job and part, and fix machine rates and overhead.
- How to Quote Injection Molding Jobs FasterHow injection molders cut RFQ turnaround: standard cost build-up, cycle time and press selection rules, resin pricing, and where AI drafts quotes for review.
- Compression vs Transfer vs Injection Rubber Molding: Which Costs Less?Compression vs transfer vs injection rubber molding cost: how tooling, cycle time, flash, runner waste and labor shift the break-even volume for each process.
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.