The cycle used to take 24 seconds. Now it takes 27. The cooling setting has not changed. Before shortening anything, find where the extra three seconds entered the sequence.
When injection molding cycle time increases, the first useful comparison is an event timeline. A total tells you that production slowed; event times tell you which interval changed. Machine fields can overlap, start at different events, or report requested durations rather than elapsed results. Adding every timer on the screen can count the same seconds twice.
Choose one clock before comparing the numbers
Define the total cycle as elapsed time between successive occurrences of the same event. Injection start to the next injection start is one possible definition. If the machine uses another definition, retain it and identify the events. Do not compare one convention with another without reconciling the difference.
Keep the cycle mode and context as well: automatic production, startup, a manual interruption, or a cycle awaiting an external action. A shift's elapsed time divided by its good-part count measures something different from an uninterrupted machine cycle. It can include downtime, rejected parts, and changes in active cavity count.
For a short review, select a traceable earlier sample window and the changed window from the same job. Record how many cycles each includes and keep the individual values. Averages can hide occasional waits. Confirm part, mold, material, recipe revision, and equipment identity before treating the windows as comparable.
An unchanged cooling interval and a longer total
Constructed teaching example. In this invented machine sequence, injection and hold occupy seconds 0–4. At second 4, two activities start: a 14-second remaining mold-closed cooling interval and screw recovery. The example requires both to finish before mold opening. Opening, part removal, and closing then take a combined six seconds. These event rules are assumptions for the exercise, not a claim about all presses.
Earlier: 24 seconds
Changed: 27 seconds
| Event | Earlier cycle | Changed cycle |
|---|---|---|
| Injection starts | 0 s | 0 s |
| Hold ends; remaining cooling interval and recovery begin | 4 s | 4 s |
| Recovery completes | 16 s | 21 s |
| Defined remaining cooling interval completes | 18 s | 18 s |
| Mold opening begins after both prerequisites | 18 s | 21 s |
| Next injection starts | 24 s | 27 s |
Recovery takes 12 seconds in the earlier cycle and 17 seconds in the changed cycle. Its duration increases by five seconds, but total cycle time increases by only three. In the earlier cycle, recovery finishes two seconds before the other prerequisite. The first two added seconds consume that margin; the next three delay opening.
The unchanged cooling interval therefore does not contradict the longer total. In this particular sequence, the difference appears between completion of the cooling interval and the start of mold opening. Shortening the cooling interval would not remove the demonstrated recovery wait.
Use the timeline's logic, not the sum of all fields
For this exercise only, the arithmetic is:
Earlier: 4 + max(14, 12) + 6 = 24 seconds.
Changed: 4 + max(14, 17) + 6 = 27 seconds.
The maximum accounts for the two activities starting together and the next event waiting for both. Simply adding injection/hold, cooling, recovery, and mechanical time would incorrectly produce 36 and 41 seconds. That method counts overlapping time twice.
Real sequences may start recovery later, overlap mechanical actions differently, or wait on another condition. Build the event relationship from the machine documentation and recorded sequence. Do not transplant the example's formula onto a controller screen just because the labels look familiar.
RJG's “Right Mold, Right Machine” describes situations where the ability to plasticize material limits cycle time, calling them recovery limited. That supports recovery as one possible timing constraint. It does not identify the reason for a delay in an unknown machine, nor does it make the article's equipment recommendations universal.
Ask for the record that distinguishes a slower action from a later start
A reported recovery duration can increase because the action itself takes longer. A recovery completion event can also arrive later because recovery started later. Those are different observations. Collect both start and completion events when available, together with the source's field definitions.
| Where the extra interval appears | Useful comparison | Do not assume |
|---|---|---|
| Injection start to hold completion | Transfer and hold events, actual durations, and the active recipe revision. | That an unchanged displayed setpoint proves identical elapsed behavior. |
| Recovery start to completion | Defined recovery duration and available cycle records before and during the change. | That the screw or drive is defective merely because the duration grew. |
| Prerequisites met to opening start | The actual readiness conditions, event log, and any documented external wait. | That all required permissions were already satisfied. |
| Opening through part removal and closing | Individual action events and identified waits in that sequence. | That motion is slower when the added time could be between motions. |
| Only occasional total cycles are long | The individual long-cycle IDs and their interruption or alarm context. | That every cycle has changed by the difference between averages. |
If records come from a press and a robot or monitoring system, establish how their timestamps align. A clock offset can look like a wait that never occurred. Note event resolution and rounding too; a coarse display may not locate a small difference precisely.
Keep “where” separate from “why”
The example localizes the added three seconds to a wait for recovery under its stated assumptions. It does not explain why recovery took longer. The follow-up should compare the applicable material, process, interruption, and equipment history, with the responsible specialist selecting any test. A timeline is a way to focus that work, not a substitute for it.
In a real sequence, there may be several simultaneous changes. State each observed interval rather than forcing the total into one cause. If the available export cannot distinguish a late start from a long duration, make that the specific missing record in the request for help.
Report the lost interval and preserve the quality decision
A finding for the teaching example
“Cycle increased from 24 to 27 seconds under the same defined start event. Recovery duration increased from 12 to 17 seconds. The defined cooling interval still ends at 18 seconds; opening now starts at 21 seconds after recovery completes. The cause of the longer recovery is unresolved.”
Restoring a shorter time does not by itself establish acceptable parts. Keep the required inspection and release decision separate from the timing result. Any authorized process change belongs in the trial record, with samples and verification. If the timer names are unclear, begin with reading process-sheet fields; if the sequence needs specialist interpretation, send a focused technical-help request containing the event definitions and original records.