How Do You Calculate 12-Cavity Machine Cycle Time?

The single-cavity station produces its first finished piece after 206 s, so adding independent cavities raises throughput without shortening the 200 s test. The key is to separate piece residence time, operator touch time, and the average interval between completed pieces.

Reject the two quick cycle-time fixes

The first quick calculation adds the full loading and unloading times to one-twelfth of the test time:

3 + (200 / 12) + 3 = 22.7 s/piece

That mixes two different models. Dividing the test by 12 treats the cavities as parallel capacity, while leaving both operator tasks undivided treats them as extra serial stages assigned to every output interval. It does not represent twelve independent cavities operating concurrently.

The second calculation gives the correct ideal long-run throughput interval but invites the wrong physical interpretation:

The operator does not load in 0.25 s or unload in 0.25 s. Each piece still requires 3 s to load and 3 s to unload. Division by 12 allocates the total cavity cycle across twelve concurrent positions; it does not accelerate either manual task.

Check: Record three separate values on the commissioning sheet: 206 s residence time, 6 s/piece operator touch time, and 17.2 s/piece ideal average output interval.

Define the measurement before calculating capacity

Use different names for quantities that are often all called cycle time:

Quantity	Calculation	Meaning
Piece residence time	3 + 200 + 3 = 206 s	Elapsed time from the start of loading one piece through the end of its unloading, when its operations occur without waiting.
Test time	200 s	Time one piece occupies its cavity for the automatic test. Adding cavities does not change it.
Operator touch time	3 + 3 = 6 s/piece	Total manual loading and unloading work required for each completed piece, excluding walking, reaching, identification, and delays.
Ideal output interval		Long-run average time per output when all twelve independent cavities remain productive and the operator keeps up.

The residence time answers, “How long is this part in the process?” The output interval answers, “How often does the process produce another part on average?” Production planning needs the second value; test traceability and work-in-process tracking often need the first.

Check: Confirm that the target being compared is expressed as average seconds per good completed piece, not elapsed time for one selected piece.

Connect each cavity as an independent pipeline

Start each cavity as soon as its load finishes. Do not wait for all twelve cavities to be loaded and then issue a common test start if independent operation is the intended design.

1. Load piece 1 from t=0 to t=3; its test then runs to t=203.
2. Load piece 2 from t=3 to t=6; its test runs to t=206.
3. Load piece 3 from t=6 to t=9; its test runs to t=209.
4. Continue the same start pattern through cavity 12. With uninterrupted loading, the twelfth load ends at t=36.

If unloading occurs immediately when each of the first three tests finishes, piece 1 finishes unloading at t=206, piece 2 at t=209, and piece 3 at t=212. The initial three-second loading offsets are pipelined; they do not each add another three seconds to the long-run average output interval.

After cavity 12 is loaded at t=36, the operator has 167 s before piece 1 reaches its test completion at t=203. That gap exists during initial filling of this twelve-cavity arrangement. It is not proof that every later unload and reload can occur on the original three-second spacing.

Check: Watch the cavity-state timestamps and verify that each test begins immediately after that cavity's load, independent of every other cavity.

Prove that the operator can service the completions

The operator performs 6 s of stated work per piece. As an aggregate capacity check, that is faster than the ideal machine demand of one piece every 17.2 s. Under the stated times alone, manual touch time is not the long-run bottleneck.

Observed symptom	Likely cause	Field check
A completed cavity waits before unloading	The operator is loading another cavity, handling another completed piece, or moving between positions.	Log test-end and unload-start timestamps; the difference is queue delay.
A free cavity waits before reloading	Unload and reload duties overlap, or parts are not staged at the cavity.	Log unload-end and next-load-start timestamps.
Actual output exceeds 17.2 s/piece	Walking, reaching, inspection, identification, rejects, or machine reset time is missing from the six-second touch-time estimate.	Time complete operator work over multiple outputs, including movement.
Tests finish together instead of staggered	The controls or operating method starts cavities as a batch.	Compare each cavity's load-end and test-start events.
The first piece takes 206 s and is treated as a throughput failure	Residence time is being compared with average output interval.	Measure several consecutive completed outputs after the pipeline fills.

With an unlimited row of cavities loaded every 3 s, test completions begin colliding with continued loading after about 66 consecutive loads because 200 / 3 ≈ 66.7. From that point, adding a three-second unload to each three-second load effectively creates six seconds of touch work per piece. The twelve-cavity station reaches its cavity limit well before that case, but unloading and reloading still need an explicit schedule.

Check: Confirm from timestamps that accumulated unload and reload queues return to zero during each operating pattern; otherwise replace the nominal six-second assumption with the measured touch-and-travel time.

Schedule unloading and reloading without hiding delays

Build a timestamp table rather than relying only on divided averages. Use one row per piece and include cavity, load start, load end, test end, unload start, unload end, next load start, and any waiting reason.

1. Stage twelve parts and load the cavities at the real walking sequence.
2. Let each cavity start independently at load completion.
3. At the first test completion, follow the intended priority rule: unload the finished piece, reload the free cavity, or service the next completed cavity.
4. Continue until every cavity has completed at least one later cycle, not merely the initial fill.
5. Mark every interval in which a completed cavity waits for the operator and every interval in which an empty cavity waits for a part.

A three-second initial load cadence does not mean the same cadence survives when unloading and reloading both become due. If an unload and the following reload are performed back-to-back, that cavity requires 6 s of operator attention. Other completed cavities may wait, and the stagger can spread. Those waits affect finite-run timing even when the long-run cavity-capacity limit remains acceptable.

If the measured movement makes repeated three-second handling impractical, reduce travel, stage parts at the point of use, or evaluate a loading magazine and automated insertion. Keep automation as a capacity and ergonomics decision based on the timestamp study, not as a correction to the arithmetic.

Check: Run the schedule until its pattern repeats and verify that no cavity's waiting time grows from one repetition to the next.

Calculate both continuous and finite-run performance

For the stated independent-cavity model, calculate ideal continuous output as:

The corresponding ideal rate is 3600 / 17.1667 ≈ 209.7 pieces/hour, assuming continuous operation, twelve productive cavities, immediate restart, and no losses. The six-second operator touch time has a separate arithmetic ceiling of 3600 / 6 = 600 pieces/hour before walking and other duties. The lower machine-capacity rate governs under those assumptions.

Startup and shutdown make a short run slower. One idealized timing expression for n complete dozens is:

Average interval = (n × 206 + 33) / (n × 12)

The term is the spread created by eleven three-second offsets from the first loaded cavity to the twelfth. For one dozen, the expression gives . As n grows, the startup term is diluted and the result approaches 206 / 12 ≈ 17.2 s/piece.

Use that expression only for the ideal timing pattern it represents. When the same operator must interleave unloads and reloads, calculate the finite run from the timestamp schedule because operator conflicts can move subsequent cavity starts.

Check: Compare both the finite-order average and the stabilized continuous average with the production target; state which one the target requires.

Verify the machine end to end

1. Start the clock at the beginning of the first load and record every cavity event.
2. Separate startup fill from the stabilized period.
3. Count good completed pieces, not test starts or occupied cavities.
4. Calculate actual average interval = elapsed stabilized seconds / good pieces completed.
5. Confirm that each individual test still lasts 200 s and that each stated load and unload still takes 3 s.
6. Compare actual output with 17.2 s/piece. Assign the difference to measured wait, travel, rejects, reset work, or unavailable cavities.
7. Repeat through enough cavity cycles for the service pattern and queues to repeat.

Get production running with a workable operator priority rule, then remove the recorded delays properly. A calculated average is commissioned only when the completed-piece timestamps reproduce it without a growing queue.

Check: Accept the arrangement only when all twelve cavities cycle independently, no service backlog accumulates, and the measured stabilized seconds per good piece meets the target.

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