Most line-balance studies count the value-adding work. The operator also loads the fixture, finds the part, picks up the tool, checks the torque and puts the finished unit on the conveyor. Those actions are where the cycle time actually goes.
Key takeaways
- Fixture load and unload time is part of the station time and should be measured.
- Poka-yoke should prevent the wrong part from fitting, not rely on operator attention.
- Material should be within one step of the operator's normal position.
- Replenishment frequency is set by bin size and takt, not by convenience.
Fixture design: locate, clamp, release
A fixture has three jobs: locate the part repeatably, hold it against the tool force, and release it quickly. The locating scheme should use a fixed datum and a pin or a nest, not the operator's judgement. A fixture that relies on the operator to “push it home” will produce variation that shows up as torque or fit problems downstream.
Loading and unloading should be possible with one hand if the other hand holds the part. A fixture with two clamps and a plug takes longer than a drop-in nest with a single toggle. Measure the load time with a stopwatch before approving the design; a two-second difference per cycle is 1,700 seconds per shift.
Poka-yoke that works
The best poka-yoke is mechanical: a pin that only fits the correct orientation, a nest that is deeper on one side, a connector that cannot be inserted reversed. A sensor-based check is the next best, but it depends on the sensor being clean and the logic being correct.
Avoid poka-yoke that the operator can bypass. A colour mark or a label is not poka-yoke; it is a reminder. If a wrong part can physically fit, it will eventually be fitted.
Tooling at the station
Tools should be suspended within reach, with a balance arm if they are heavy. A torque tool should be programmed for the joint and should record the result if traceability is required. The tool cable should not cross the part or the operator's body.
For multiple tools at one station, use a tool balancer with a selector or a quick-change holder. A station with three tools on the bench and one in the operator's hand has a hidden search time that rarely appears in the process sheet.
Material presentation
The operator should be able to reach the part without turning or walking. The ideal zone is about 500 mm wide and 300 mm deep at waist height. Parts used most often should be closest. Parts used once per cycle can be slightly further away.
Bins should be angled toward the operator and should not be filled above the level where the operator has to dig. A bin that is filled to the top saves replenishment time but adds picking time. The right fill level is the one that keeps the pick time constant.
| Material | Presentation | Replenish trigger |
|---|---|---|
| Small parts, high usage | Gravity bin at waist height | Kanban card or sensor |
| Large parts | Flow rack beside the station | Empty slot |
| Kits | Kit cart sequenced to the line | Kit consumed |
| Consumables | Dispenser within reach | Visual level |
| Tools | Balancer or holster | Not applicable |
Replenishment and line-side inventory
Line-side inventory should be measured in minutes of production, not in days. A line that holds four hours of inventory has four hours of hidden problems. A line that holds 30 minutes needs a reliable replenishment route and a trigger that works.
For a line with a 12-second takt and a bin that holds 60 parts, the bin lasts 12 minutes. If replenishment takes 10 minutes, the line will run out. Either increase the bin, add a second bin, or shorten the replenishment route. The calculation is simple and should be done before the line is laid out.
Ergonomics and cycle time
Working height should be 50–100 mm below the operator's elbow height for precision work, and slightly lower for force work. A height that is wrong by 100 mm adds fatigue over a shift and slows every cycle. Anti-fatigue mats and sit-stand options are cheaper than the output lost to fatigue.
Lighting should be adequate for the inspection task, and should not create glare on the part or the screen. For fine assembly, 750–1,000 lux at the work surface is a reasonable target.
Frequently asked questions
Should fixtures be dedicated or adjustable?
Dedicated fixtures are faster and more repeatable for high-volume models. Adjustable fixtures are better for high-mix, low-volume production, but they must be designed so that adjustment is quick and cannot be set incorrectly.
How often should material be replenished?
Set the interval so that the bin never empties between replenishments, with a margin of at least one replenishment cycle. For most lines, 30–60 minutes of material at the station is a practical target.
Do I need a tool balancer?
For tools above about 2 kg, yes. A balancer reduces fatigue and prevents the tool from being dropped on the product.
Send the station layout and part list to our engineers through the contact page; we will review fixture and material presentation with the line design.
