Most balancing problems are created before the balance chart exists. An operation is split that cannot be split, or two operations are combined that share a fixture, or a test is placed downstream of the station that needs its result. The method below starts with constraints, not with arithmetic.
Key takeaways
- List operations with their precedence and their equipment, not just their time.
- Some operations cannot be separated: adhesive cure, torque sequences, tests with a fixed dwell.
- Station content at 85–90% of takt leaves room for variation.
- Walk time between positions is part of the station time.
Step 1: list operations with constraints
For each operation, record the time, the tool, the fixture, the skill and the precedence. Two operations with the same fixture often belong at the same station even if the times allow separation, because moving the part between stations adds handling and error. An operation that must follow a cure or a test has a hard precedence that cannot be balanced away.
Step 2: calculate takt and target content
Takt is available time divided by required output. If the line runs 430 minutes and must produce 2,150 units, takt is 12 seconds. Target station content is 85–90% of takt, or 10.2–10.8 seconds. Anything above 12 seconds cannot meet rate without overtime or a second operator.
Step 3: group operations into stations
Start from the operations with the hardest precedence and work outward. Group by fixture and by test dependency first, then by time. A station can hold several small operations if they use the same fixture and the operator can reach them without walking.
Do not create a station that is just below takt by a fraction of a second. That station will be the bottleneck on every cycle where anything varies. Leave a visible margin.
| Operation | Time | Constraint | Station |
|---|---|---|---|
| Place housing in fixture | 3.0 s | Fixture A | 1 |
| Insert gasket | 3.5 s | Fixture A | 1 |
| Fit PCB | 4.0 s | ESD | 2 |
| Torque 4 screws | 6.0 s | Torque tool, sequence | 2 |
| Functional test | 9.0 s | Test dwell | 3 |
| Label and pack | 5.0 s | — | 4 |
Step 4: add walk and handling
An operator who walks 1.5 m between two positions adds about 1.5 seconds. A operator who has to turn, pick up a tool and return adds more. These times are real and should be measured, not estimated from a layout drawing.
If the walk time pushes a station over takt, the answer is usually to change the layout, not to ask the operator to move faster. A U-shaped cell or a double-sided line can reduce walking without adding stations.
Step 5: test the balance with variation
Run a simple model with ±10% variation on each operation and see which station becomes the bottleneck. If the same station is the bottleneck in most cycles, rebalance. If the bottleneck moves, the line may need a buffer rather than a new balance.
For mixed-model lines, balance for the longest model and check that the shortest model does not create idle time that tempts operators to work ahead. Working ahead breaks the sequence and can cause missing parts or skipped tests.
What balancing cannot fix
Balancing cannot fix a process that is not capable. If a torque operation takes 6 seconds but fails 8% of the time, the station needs a rework path and a buffer, not a smaller station time. Balancing also cannot fix a fixture that requires two hands and a foot pedal; that is a tooling problem.
Before rebalancing an existing line, measure the actual station times for a full shift. The times in the process sheet are often 10–20% different from what operators actually do.
Frequently asked questions
How many stations should one operator run?
Two adjacent stations are common if the combined content is below 85% of takt. Three stations usually require the line to stop long enough for the operator to move between them.
Should I balance for the average or the slowest operator?
Balance for a competent operator at a normal pace, then add a variation allowance. Balancing for the slowest operator over-staffs the line; balancing for the fastest under-staffs it.
Can a line run at 100% balance?
Only briefly. A line designed at 100% has no recovery margin, and the first variation propagates. Plan for 85–90% and use buffers for the rest.
Send your operation list and target output to our engineers via the contact page; we will return a station balance and a layout concept. Our assembly line section covers fixture and material feed design.
