Line efficiency is earned minutes divided by available minutes. When it is low, either the line earned fewer minutes than it should, or it had more minutes than were used. The job is to find out where the minutes went.
Step 1: Check the number itself#
Before changing anything on the floor, make sure the efficiency calculation is right:
- Is the SMV correct? A SMV that is too low for the real method makes efficiency look poor. Compare with a time study of key operations.
- Is output counted consistently? Only good garments passed at end of line, or all garments?
- Is manpower counted correctly? Operators only, or helpers, ironers and checkers too? Match the definition used in the target.
- Are minutes right? Include overtime minutes if overtime output is counted.
See line efficiency for the formula and definitions.
Step 2: Look at the hourly pattern#
Plot hourly output against the hourly target:
| Pattern | Likely cause |
|---|---|
| Low all day, steady | Bottleneck or imbalance; SMV issue |
| Low in the first hours | Slow start, no WIP at the start of the day, late cut issue |
| Drops at certain hours | Feeding gaps, machine breakdowns, breaks running long |
| Low near the end of the day | Fatigue, end-of-order changeover, WIP running out |
| Low for the first days of a style | Learning curve (normal, but check it is improving) |
Step 3: Measure lost time#
Record every stop longer than a few minutes with its cause, for at least a few days:
| Lost time cause | What to check |
|---|---|
| Machine breakdown | Mechanic response time, repeat breakdowns, preventive maintenance |
| Waiting for work | Cutting delays, missing bundles, bundle tracking |
| Waiting for trims | Store issue process, BOM accuracy |
| Style changeover | Pre-planning, machine setup before the change |
| Quality stops | Repairs, rework loops |
| Meetings and training | Scheduled during production hours? |
| Power and utilities | Generator switchover, compressed air |
Lost time is often the largest single loss, and much of it is outside the operators' control.
Step 4: Check the balance#
Carry out a quick capacity study at each station and find the bottleneck. If one station is at 70 pieces per hour and the target is 100, the line cannot exceed 70. Rebalance using line balancing.
Step 5: Check quality losses#
Rework takes time from operators and does not add output. Look at:
- End-of-line DHU and the top defect types
- Garments returning to the line for repair
- Operators doing their own repairs during production
Step 6: Check people#
- Absenteeism: replacements working on unfamiliar operations.
- Skills: are the right operators on the critical operations? Use a skill matrix.
- New operators: training plan and support.
- Motivation: targets that are unrealistic are often ignored.
Step 7: Check methods and workplace#
- Handling time: bundle position, tying and untying, repositioning.
- Missing guides and attachments.
- Poor lighting, chair heights and table layouts.
See motion study.
Prioritise#
After a week of data, list the losses in minutes per day and fix the biggest first. A typical order is: lost time, bottleneck, rework, then methods and skills.
Quick checklist#
- SMV and efficiency definitions checked
- Hourly output pattern plotted
- Lost time recorded by cause
- Bottleneck identified and addressed
- Top defects and rework measured
- Operator allocation reviewed with the skill matrix
- WIP levels checked. See WIP control