A sewing line is only as fast as its slowest operation. Everyone on a production floor knows this, and still most lines are managed as if their output were the sum of everyone's effort. What you want is to find, today, the operation that is holding your line back, fix it or protect it, and know when the bottleneck has moved somewhere else — because it will. This article shows how to find it with nothing more than a count and a watch, what to do about it, and how to keep it visible.
Why one operation sets the pace for the whole line
A garment passes through a sequence of operations. Each has a capacity: how many pieces per hour the operators assigned to it can complete. The line cannot produce more finished garments per hour than its lowest-capacity operation, however fast the others work. The Theory of Constraints puts it generally — every system has a constraint that limits its output — and the International Labour Organization's lean manual for the garment industry defines the bottleneck in the same terms: a process that constricts or limits the flow.
Two consequences follow, and both are counter-intuitive on a busy floor.
- An hour lost at the bottleneck is an hour lost for the whole line. An hour lost anywhere else may cost nothing, because that operation had spare capacity.
- Speeding up an operation that is not the bottleneck produces work in progress, not garments. It piles up in front of the bottleneck.
Step one: know the pace the line needs
Takt time is the pace demand requires: the available production time divided by the number of pieces needed in that time. If a line has 480 minutes and must deliver 720 pieces a day, its takt time is 40 seconds: a finished garment every 40 seconds. Any operation that cannot keep up with that pace, with the operators assigned to it, is a bottleneck against the plan.
Step two: calculate each operation's capacity
For each operation, capacity per hour is:
Capacity per hour = (60 ÷ standard minutes for the operation) × operators assigned × their efficiency
An illustrative example: an operation with a standard time of 0.8 minutes, one operator working at 75% efficiency, can produce (60 ÷ 0.8) × 1 × 0.75, about 56 pieces an hour. If the line's target is 90 an hour, this operation is the bottleneck by a wide margin, and every other operation's extra speed is wasted until it is fixed. Laid out for all operations on a simple chart, capacities against the target, the bottleneck is the lowest bar. How garment factories calculate production efficiency explains where the standard times and efficiencies come from.
Step three: confirm it on the floor
The calculation tells you where the bottleneck should be. The floor tells you where it is. Three signs point to it directly.
- Work piles up in front of it. Count the bundles waiting at each operation at fixed times — say every two hours. The operation with a growing queue in front of it is the bottleneck, or is being starved and fed unevenly by one.
- Operators after it wait. Look for operators downstream who are idle, rearranging bundles or helping elsewhere.
- Its hourly output matches the line's. If the end-of-line output per hour is the same as one operation's output per hour, that operation is setting the pace.
A few timed cycles of the suspected operation will tell you whether the problem is its standard time, the operator's method, the machine, or simply too few people assigned.
Step four: fix it, or protect it
There are two kinds of response, and a good line manager uses both.
Raise its capacity:
- Add an operator, or split the operation so part of it moves to a neighbour with spare capacity.
- Move a multi-skilled operator onto it when it falls behind.
- Improve the method: a folder, a guide, an attachment or a better workstation layout can take seconds off each cycle.
- Check the machine: a bottleneck on an unreliable machine is a bottleneck twice.
Protect it from losing time:
- Keep a small buffer of work in front of it so it never waits.
- Stagger breaks so it keeps running when others stop, if the arrangement allows.
- Service its machine first and keep a spare nearby.
- Check quality before it, so it never spends its scarce time on pieces that will be rejected.
The bottleneck moves
A line balanced for one style is unbalanced for the next. An absent operator creates a bottleneck where there was none. A machine failure moves it for an hour. That is why finding the bottleneck is not a one-off exercise but a daily one, and why it needs data that arrives during the shift rather than the next morning.
Where tracking is done on paper or through a group chat, the only record of a moving bottleneck is the supervisor's impression, and the lost hours are discovered in the day's total. Paper, WhatsApp and old Windows programs: how garment factories lose production time looks at how much of that loss is simply the time between a stoppage and a response.
What to record so the bottleneck stays visible
- Hourly output at the end of the line against the target.
- Work waiting at each operation, counted at fixed times.
- Stoppages at each operation, with a reason and a duration.
- Operators assigned to each operation that day.
With those four, the bottleneck shows itself: output falls short, work piles up in one place, and the stoppage log says why.
The next step
Tomorrow, count the bundles waiting at every operation on one line at ten, twelve and two o'clock, and write the numbers on the operation breakdown. By two o'clock you will know where your bottleneck is. Softwiro builds production tracking that records output, waiting work and stoppages per operation as they happen; if you want the bottleneck to be visible on a screen rather than found by walking the line, tell us how your line is organised.
Sources
- Lean Manufacturing Techniques for the Ready-Made Garments Industry — International Labour Organization, Cairo office. Defines the bottleneck and line balance for garment production.
- Theory of Constraints — Theory of Constraints Institute. Every system has a constraint that limits its output.
- Takt time — Lean Enterprise Institute. Available production time divided by customer demand.
- Introduction to Work Study, fourth revised edition — International Labour Office. Time study and standard time for each operation.