The output of a sewing line is set by its slowest station. If one operation can only produce 60 pieces an hour, the whole line produces 60 pieces an hour, no matter how fast the other stations are. That station is the bottleneck. Improving any other station adds WIP, not output.
Signs of a bottleneck#
- WIP piles up in front of one station and is thin after it.
- Operators after the station wait for work.
- The station's operator never has a pause and is often under pressure from the supervisor.
- Hourly output stays flat even when more people are added elsewhere.
WIP is a sign, not proof. A pile can also form because a feeding operator just delivered a large bundle. Confirm with a capacity study.
Step 1: Capacity study#
For each station, time several cycles and calculate the hourly capacity:
Use actual observed cycle time, including handling, not the SMV. Take enough cycles (at least 5 to 10) at a normal pace. See time study for method.
Step 2: Plot the station capacities#
List stations in sequence with their hourly capacity and draw a simple bar chart against the line target. The lowest bar is the bottleneck. Several bars below the target show a line that cannot reach the target without rebalancing.
| Station | Operation | Capacity/hour |
|---|---|---|
| 1 | Shoulder join | 142 |
| 2 | Neck rib attach | 88 |
| 3 | Neck topstitch | 118 |
| 4 | Sleeve attach | 96 |
| 5 | Side seam | 104 |
| 6 | Hem | 126 |
Target: 100 per hour. Station 2 (88) and station 4 (96) are below target. Station 2 is the bottleneck.
Step 3: Find out why#
Common reasons a station is slow:
| Reason | What to check |
|---|---|
| Too much work content | Compare the station SMV with pitch time |
| Operator skill | Compare the operator's cycle time with a skilled operator on the same operation |
| Method | Handling, positioning, bundle opening, unnecessary movements |
| Machine | Speed, stops, thread breakage, missing attachments or guides |
| Quality | Repairs coming back to the station |
| Supply | Waiting for parts, trims or bundles from cutting |
Step 4: Raise the bottleneck output#
In order of cost and speed:
- Remove non-value work from the bottleneck (trimming, bundle tying, counting). Give it to a helper or another station with spare time.
- Improve the method: better workplace layout, guides, folders and attachments. See motion study.
- Fix the machine: stop repeated thread breakage, set the right speed.
- Move part of the work to an under-loaded station with the same machine type.
- Place a stronger operator at the station, using the skill matrix.
- Add an operator or machine if the work content is simply too high.
Step 5: Check again#
After fixing the bottleneck, the constraint moves to the next slowest station. In the example above, raising station 2 to 110 per hour makes station 4 (96) the new bottleneck. Keep going until every station is above the target or the balance is as good as the line can achieve.
Beyond the sewing line#
The bottleneck is not always in sewing. Cutting, embroidery, printing, washing or finishing can limit the whole factory. Apply the same logic: find the slowest process, protect it from interruptions, and raise its output before adding capacity elsewhere.
Related: line balancing, WIP control and low line efficiency troubleshooting.