Autoclave Cure Cycle Time and Capacity Calculator
Autoclave time is usually the bottleneck in a composites plant, so a cure cycle that is an hour longer costs real capacity. This calculator turns your ramp rates, dwells and cooldown into total cycle time and then into runs and parts per week.
Your numbers
Intermediate hold for resin flow and debulk. Use the same as the cure temperature if your cycle has a single dwell.
Limited by the specification and by the thermal lag of the tool and part.
Often limited to 3 C/min or less to avoid thermal stress and spring-in.
Extra time for the coldest part thermocouple to reach each hold temperature.
168 hours less maintenance, holidays and unplanned downtime.
Your results
Planning estimate. Real cycles are governed by your qualified cure specification, thermocouple response and customer-approved recipe. Do not change recipes based on this tool.
Cycle time (hr) and runs per week versus heat-up rate
Sweeps Heat-up rate from 0.5 to 6, holding your other inputs fixed.
Plan autoclave loads from live demand
Optional: see how open work orders and tool data can feed an autoclave load and schedule planner.
Optional. The tool and every export work without this. No spam.
How to use the calculator
Enter the start temperature, the first dwell temperature and time, the cure temperature and time, and the heat-up and cooldown rates from the cure recipe. Add a thermal lag allowance, which accounts for the part and tool lagging the air temperature at each hold. Then enter turnaround time for loading, connecting vacuum and unloading, the weekly hours the autoclave can run and the parts per run. The primary results are cycle time and runs per week. The chart shows how faster heat-up shortens the cycle, which is useful for weighing the benefit of a rate that is already near the specification limit.
- Set the first dwell equal to the cure temperature and its time to zero for a single-step cycle.
- Use measured lag from earlier runs for the thermal lag allowance.
- Check cooldown against the maximum rate in the cure specification.
The arithmetic
Heat-up time is the temperature rise divided by the ramp rate. The default two-step cycle (22 C to 110 C, hold 60 min, then to 180 C, hold 120 min) has 44 minutes and 35 minutes of ramping, 180 minutes of dwell, and about 48 minutes of cooldown to 60 C at 2.5 C/min, plus 50 minutes of lag allowance. That totals about 6.9 hours of program run. Adding 2.5 hours of turnaround gives a 9.4 hour slot and 12 runs in a 120-hour week. Utilization shows how much of the available time is consumed by the schedule at that run count.
Using the results for planning
Capacity equals runs per week times the parts loaded per run, but parts per run is often constrained by tool size, so check it with the process engineer. Because a significant part of the cycle is dwell time that cannot be shortened, the sensitivity to ramp rate is smaller than people expect; doubling the ramp from 2 to 4 C/min saves only about 40 minutes. Reducing turnaround, increasing loading or combining compatible cure recipes in the same run usually delivers more capacity than chasing ramp rates.
Common mistakes
Planners often use the controller set-point ramp and ignore the lag of heavy tools, so the real cycle exceeds the plan. Cooldown is a second trap: it is frequently the longest ramp and is limited by the autoclave's cooling capacity at lower temperatures, so the final degrees take longer than a constant rate suggests. Mixing parts with different cure recipes in one load forces the longest and most conservative cycle on all parts. Finally, preventive maintenance and vacuum or leak problems reduce available hours, so do not plan to 100% utilization.
Frequently Asked Questions
How long is a typical autoclave cure cycle?
Aerospace epoxy prepreg cycles typically run from about 4 to 12 hours of program time, depending on the dwell structure, heat-up and cooldown rates and part thickness. Heavy tools and thick parts add thermal lag and lengthen the cycle.
What heat-up rate is typical for composite cure?
Many epoxy prepreg specifications call for 1 to 3 C per minute, measured on the part. Faster rates risk exotherm and uneven cure in thick laminates, while very slow rates waste capacity. Always follow the qualified recipe for your material.
Why is cooldown often the limiting step?
Autoclaves cool by circulating gas through a heat exchanger, and the temperature difference to the coolant shrinks as the load cools, so the rate drops near the end. Specifications also cap the rate to limit residual stress and warpage.
Can I cure different parts together in one run?
Only if they share a compatible recipe, with thermocouples on every part type and a cycle that meets the most demanding requirement. Mixed loads need engineering approval and a defined way to control the cycle from the coldest thermocouple.
If your autoclave schedule and tool loading are in an ERP or MES, Netray can help build a scheduling assistant that proposes load plans and shows capacity against demand, on-premises if required.
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