How to Calculate Flow Time of Cutter in Flow Wrap?

Shree Narayan Machines

April 2, 2026

How to Calculate Flow Time of Cutter in Flow Wrap?

In horizontal flow wrapping (HFFS) the cutter must operate in perfect sync with the film feed and infeed conveyor. Cutter flow time (also called cutter cycle time or dwell time) is the time window during which the cutter engages, seals, and separates a pack while the product is stationary (intermittent) or while the cutter moves with the product (flying shear).

Key variables and formula

Important variables

$P$ = product pitch (distance between product centers) in mm.
$V_{f}$ = film linear speed (mm/s).
$N$ = target packs per minute (ppm).
$T_{c}$ = cutter cycle time (s) — the value to calculate.
$t_{d}$ = cutter dwell or engagement time (s) — mechanical requirement for seal formation.

Basic relationships

Packs per second $= \frac{N}{60}$ .
Product pitch $P = \frac{V_{f}}{packs per second}$ .

Cutter cycle time formula

$T_{c} = \frac{1}{packs per second} = \frac{60}{N}$

Dwell requirement

$t_{d} \leq T_{c} and t_{d} \geq t_{seal}$

where $t_{seal}$ is the minimum seal time determined by film and sealer temperature/pressure.

Worked example (practical)

Target: 600 ppm (common mid‑high speed line).
Packs per second = $600 / 60 = 10$ packs/s.
Cutter cycle time $T_{c} = 1 / 10 = 0.1$ s (100 ms).
If the sealer requires 30 ms to form a reliable seal, set cutter dwell $t_{d}$ to 35–40 ms to allow margin. Ensure cutter actuation and blade travel fit within the remaining 60–65 ms for acceleration/deceleration or flying shear motion.

Table — quick parameter checklist

Parameter	Symbol	Typical value	Why it matters
Product pitch	P	50–200 mm	Determines film advance per cycle
Target speed	N	100–2000 ppm	Sets cutter cycle time
Cutter cycle time	T_c	$60 / N$ s	Synchronization baseline
Dwell time	t_d	20–100 ms	Seal integrity requirement
Film speed	V_f	mm/s	Must match conveyor & cutter timing

Practical tips to reduce scrap and improve timing

Measure actual film slip with a tachometer; adjust $V_{f}$ in PLC to match theoretical pitch.
Use servo‑driven cutters for precise acceleration profiles and repeatable $t_{d}$ .
Validate seal time experimentally: run a seal‑strength test at different $t_{d}$ and temperatures.
Account for mechanical lag: include actuator response time in $t_{d}$ budget.
Implement closed‑loop feedback (encoder on film and cutter) to auto‑correct drift.

Troubleshooting checklist

Cutter misses sync: check encoder wiring and PLC phase alignment.
Weak seals: increase $t_{d}$ or sealer temperature; check film compatibility.
Excessive scrap at high speed: reduce acceleration, use flying shear, or increase lanes.

Conclusion

Calculating cutter flow time is a mix of simple timing math and empirical validation. Start with $T_{c} = 60 / N$ , allocate safe dwell $t_{d}$ for sealing, and validate on the line with real film and product. For a tailored calculation, share product dimensions, target ppm, and film type, and I’ll produce a step‑by‑step timing sheet and PLC parameter set.

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