Line balancing: how to split work so a line meets takt

Three calculations frame a simple serial line:

These describe how evenly work is split in the model. They are not a measure of factory performance. Always say which reference cycle you used. In the example below it is the longest station time, while each station is still checked against takt separately.

Build the study on direct observation and a written work sequence, not a list of average times. An observation sheet with these fields keeps the assumptions visible:

Start with enough detail to explain today's limit, then refine where uncertainty affects a decision.

Record interruptions separately. A missing component or a tool fault belongs in the loss record, not folded into the assembly time, where it would hide the cause. Observe more than one shift, product variant and trained operator, and note the conditions. The aim is a baseline you can defend, not the fastest demo anyone managed.

Beyond the chart, three kinds of technique help with harder lines:

Compare several assignments rather than taking the first that works. A slightly less even split may be better if it avoids a second fixture or moving a sensitive quality check. Before accepting an optimized answer, write down what better means: meeting demand with today's resources, lowering the longest station or minimizing disruption.

An illustrative four-station serial line: one unit per cycle, fixed task times, no parallel work and no downtime or defects. Available time is 25,200 seconds a shift and demand is 420 units.

Takt = 25,200 ÷ 420 = 60 seconds a unit

The current assignment:

Station 2 sets the pace. At 75 seconds, the line can make 25,200 ÷ 75 = 336 units a shift, short of the 420 needed. Total work is 210 seconds, so balance efficiency with 75 seconds as the reference is 210 ÷ (4 × 75) = 70%.

Suppose the element review finds moves that keep the sequence, tools and quality checks intact:

Total work content is still 210 seconds; no task got faster. But the longest station drops from 75 to 55 seconds. Balance efficiency becomes 210 ÷ (4 × 55) ≈ 95.5%, and modeled capacity rises to about 458 units a shift. That is a capacity figure, not an instruction to make more than demand.

Could three stations do it? 210 ÷ 60 = 3.5, rounded up to four. Three stations at a 60-second cycle offer only 180 seconds of work time, which is not enough for 210 seconds of work.

The pilot still has to answer what the math cannot: whether the moved tasks fit physically, whether material arrives in time and whether operators can hold the new sequence. Keep the calculation and the validation record together.

Spare seconds at a station are not enough reason to send it more work. Walk through the full task at the receiving station with the people who will do it, and check:

• Reach and posture: The positions needed through the full sequence, including rare actions.
• Tools and fixtures: Whether they can be supplied without blocking nearby work.
• Material presentation: Where each part arrives and how empty containers leave.
• Quality controls: Inspection access, identification and any traceability steps.
• Shared space: How neighboring operators work at the same time, not each one alone.
• Replenishment: Run the station while material is being restocked, not only with every bin full.

OSHA's ergonomics guidance asks that workstations fit the people using them, leave room to move and limit awkward postures, repetition and force. Use it as a prompt, not a substitute for a task-specific ergonomic review.

Where an operator loads a machine and walks away during its cycle, mark exactly when loading ends, when the automatic cycle starts and when the operator must return, including unloading and checks. Have engineering and safety review the overlap before a trial; a timing diagram does not prove safe access.

Start with the decision, not the product category. For a small, clear problem, a maintained spreadsheet and a yamazumi chart may be enough. For many variants and constraints, prepare a test data set with real models, resource limits and at least one hard case, and ask each vendor to show:

• Time types: Separate manual, walking, automatic and setup time where you need it.
• Sequence control: What happens when a proposed move breaks a dependency.
• Resource limits: Blocking or flagging assignments without the right equipment or skill.
• Scenarios: Comparing options without overwriting the approved baseline.
• Change control: Who changed an assignment and which plan is current.
• Data exchange: Imports, exports and who owns the source data.
• Everyday use: Letting the people who maintain the balance make a real update.

Ask for an infeasible case in the demo. Spotting a bad assignment matters as much as drawing a good one. The time study software category lists tools that capture the element times these packages depend on.

Set the acceptance criteria before changing the line, so everyone knows what evidence will count:

1. 1

   Set scope and owners. Name the product family, stations, shifts and owner. Involve operators, supervision, engineering, quality, maintenance and safety.

2. 2

   Save the baseline. Keep current assignments, output records, staffing and known losses, with the conditions attached to each measure.

3. 3

   Review the proposal. Check task order, equipment, material supply, quality controls and physical fit. Settle disagreements before the trial starts.

4. 4

   Prepare people and material. Train the new sequence, set out tools and parts and arrange support. Do not count the first unfamiliar cycles as normal.

5. 5

   Run and watch. Record good units, interruptions, difficult tasks and any extra help needed, and note which variants were actually tested.

6. 6

   Accept, revise or reverse. Compare results with the criteria, and keep a clear path back to the old setup.

After acceptance, update the work instructions and point-of-use information. A balance is not finished while output depends on an unlisted helper, temporary part staging or a supervisor stepping in again and again.

The work split is only one part of output. When the line falls short, check in this order:

Product mix often hides overload. An average across models can sit under takt while the hardest model sits well over it. Test each variant at each station, and look at the order models will arrive in. If the plan depends on alternating easy and hard units, write that down and schedule for it with heijunka.

Balancing should reduce unevenness, not move it. A new assignment that leaves operators rushing one cycle and waiting the next has traded one overloaded station for mura. The muri guide covers how unevenness and overburden feed each other.

Judge the balance by sustained production, not by how neat the chart looks. Keep balance efficiency next to these:

• Good output against demand: Did the setup make the needed quantity?
• Station load against takt: Which stations still run close to the line?
• Labor hours per good unit: Did resource use improve without hidden help?
• First-pass quality: Did the new sequence keep quality where it was?
• Stops and assistance: What kept the sequence from repeating?
• Operator feedback: Which tasks still feel hard or unstable?

Compare like with like. If staffing, mix, overtime or equipment changed, say so rather than crediting line balancing with everything. Set review triggers as well as dates: a new option, an engineering change, a fixture change or a new shift pattern should prompt a fresh check.

1. 1

   Using takt as if it were cycle time. The pace customers need is not proof the line can hold it.

2. 2

   Balancing on averages across models. The hardest variant can overload a station the average says is fine.

3. 3

   Ignoring precedence. Moving a task ahead of the step it depends on.

4. 4

   Folding stops into task times. Breakdowns and shortages disappear into the averages.

5. 5

   Moving work for spare seconds alone. Without checking reach, tools, material and quality access.

6. 6

   Calling the chart the result. Equal bars are a plan until a pilot shows repeatable good output.