Line Balancing Efficiency

Also known as balance efficiency · assembly line efficiency · balance delay · line efficiency · station idle time · how well is the line balanced

E = \frac{\sum t_i}{N\,C}

E =

ΣT =

N =

C =

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Stations get paid for the whole cycle whether they are working or waiting. Five stations on a 100-second cycle buy 500 station-seconds per unit built; if the work only fills 400 of them, efficiency is 80% and the other 100 seconds are balance delay. That idle time is real money, and on a line running two shifts it is the equivalent of a full-time position.

Efficiency is capped by the longest single task. The cycle time can never be shorter than the biggest indivisible task on the line, so one 95-second operation forces a 95-second cycle even if the average station only holds 60 seconds of work. This is why line balancing so often turns into task splitting: break the bottleneck task in half and the whole line's cycle can drop, lifting efficiency at every station at once.

The number to distrust is a very high one. Efficiency above about 95% usually means the cycle time was fitted to the work rather than to customer demand, which is a line balanced to itself instead of to takt. It will look wonderful on the report and build inventory nobody asked for.

Line Balancing Efficiency

E = \frac{\sum t_i}{N\,C}

Where

$E$ = Balance efficiency
$\sum t_i$ = Total work content (s)
$N$ = Number of stations (stations)
$C$ = Cycle time (s)

Missing one of these? Work it out first, then come back

Balance efficiency — Thermal Efficiency, Machine Efficiency
Total work content — Theoretical Minimum Number of Stations, Reorder Point
Number of stations — Theoretical Minimum Number of Stations, Economic Order Quantity (Wilson EOQ)
Cycle time — Theoretical Minimum Number of Stations, Little's Law (Work in Process)