Cycle Time Calculator
Calculate total injection molding cycle time from injection, packing, cooling, and mold open/close times.
Introduction
Cycle time is the denominator of every injection molding cost calculation: parts per hour, machine-hour absorption, and quoted piece price all flow from it. The Cycle Time Calculator builds total cycle from its four physical phases — injection (fill), pack/hold, cooling, and mold open/eject/close — so you can see exactly where the seconds go instead of treating the cycle as one opaque number. Enter the four phase times from estimates or from the press controller and it returns total cycle, which converts directly into hourly output and cost per part for quoting and capacity planning.
How it Works
The sum is t_cycle = t_inject + t_pack + t_cool + t_open_close, mirroring the sequential phases of the molding process. Each input is independently estimable: fill time from shot volume and injection rate, pack time from the Hold Time Calculator's gate-freeze estimate, cooling from the Cooling Time Calculator's conduction model, and open/close from dry-cycle specs plus ejection strokes. Because the phases simply add, the breakdown immediately ranks improvement targets — on most parts cooling is 50–70% of the total, making it the first place to attack.
Usage Scenarios
- Quoting a new job: assembling a defensible cycle estimate phase-by-phase before the tool is built, then converting to parts per hour for the cost model.
- Kaizen on a running job: comparing actual controller phase times against calculated estimates to find which phase carries hidden padding.
- Evaluating a robot upgrade — if open/eject/close is 8 s of a 32 s cycle, faster part removal attacks a quantified 25% slice.
- Capacity planning: translating a forecast volume increase into required press-hours using the calculated cycle and cavity count.
- Justifying conformal cooling: plugging the reduced cooling estimate into the sum shows the payback period for the tooling investment.
FAQ
Which phase should I optimize first?
Almost always cooling — it typically dominates the sum. Wall-thickness reduction, better circuit layout, and optimal coolant temperature deliver more seconds than shaving fill or clamp motion.
Are the four phases strictly sequential?
Pack and early cooling overlap physically — cooling starts the instant melt touches steel — but controllers timestamp them sequentially, and the additive model matches how presses report and how jobs are quoted.
What is a realistic open/close time?
Small presses with short strokes manage 2–4 s; large tools with long ejection strokes, side actions, or sweep robots can need 8–15 s. Use the actual dry-cycle plus ejection measurement when available.
How do I turn cycle time into cost per part?
Parts per hour = 3600 ÷ t_cycle × cavities. Divide the machine-hour rate by that figure and add material and labor to get the molded piece cost.