Takt the pulse
The ideas behind takt time and how it forms the fundamentals for determining the speed of production has always amazed me — how it was used as a pacing clock (or pulse) to produce B-24 bombers where one B-24 is produced once every hour [1] and how it lives within lean manufacturing across a multitude of companies today. Essentially, takt time ensures that goods flow through each linked workstation in the most efficient manner.
Line balancing and Takt time
Line balancing works by assigning tasks to a series of linked workstations in a manner that (i) minimises the number of workstations and (ii) minimises the total amount of idle time at all stations for a given output level. A line is perfectly balanced when the amount of work assigned to each workstation is identical. This is hardly the case in practice — most lines are unbalanced in reality — as the actual amount of work varies from one workstation to the next.
There are five basic steps to perform line balancing:
1. Identify all the process steps required including the time for each task, the immediate predecessor for each task and the total time for all tasks.
2. Draw a precedence diagram. This will be used when assigning individual tasks to workstations.
3. Determine the take time for the line:
Takt time = Available production time / Required output rate
This tells us the maximum allowable time between completions of successive units on the line.
4. Compute the theoretical minimum number of workstations needed:
Number of workstations = Total time for all tasks / Takt time
With fractions, round up. Note that the shorter the required takt time, the more workstations we will require.
5. Use a decision rule to assign tasks to the workstations. Start with the first workstation and add tasks until we reach the point at which no more tasks can be assigned without exceeding the takt time (best effort). Once this point has been reached and all the tasks have yet to be assigned, repeat the assignment process with the next workstation.
Some common decision rules are:
- assign the largest eligible task that will still fit within the workstation without exceeding takt time
- assign the eligible task with the most tasks directly dependent on it
- assign some combination of the above
A quick example
A contract manufacturer produces 900 units per 8-hour day and the total time for all tasks is 302 seconds. Compute the takt time and the number workstations required.
Takt time = 8 * 60 * 60 seconds / 900 units per day = 32 seconds
Number of workstations = 302 seconds / 32 seconds = 9.43 ≈10 workstations
Some nuggets
1. Most line are unbalanced in reality
2. Line balancing facilitates a streamlined flow of the production process
