Understanding a process’ cycle time is extremely important, especially in the context of takt time. In a mixed model environment, cycle time can be a bit less straight-forward. That’s where weighted averages may make sense.
Weighted average cycle time, also known as “average weighted cycle time,” provides a representative average cycle time. Varied models or services in a given cell, line or work area often have varied work contents due to different steps, duration of steps, sequence of steps, etc. Accordingly, the cycle times vary.
Weighted average cycle times can be calculated for operator cycle times, machine cycle times and effective machine cycle times. Often weighted average cycle times are presumed to be operator related, but this is not always the case.
As we endeavor to maintain a cycle time that is less than or, at most, equal to takt time, mixed models and their varying work content will likely have cycle times for some products or services that are below takt time, while others exceed takt time. The weighted average cycle time serves as an average proxy for cycle time and is often the same as the planned cycle time.
Clearly, change in product or service mix will change the weighted average cycle time. As the demand mix shifts to one with a greater proportion of cycle time(s) that exceed the average, then the weighted average cycle time will approach and may exceed takt time. The lean practitioner must be aware of these dynamics and should proactively address the situation through reducing work content, optimizing balance between operators, adding additional operator(s) or lines, strategically applying/sizing FIFO lanes, etc.
See below for the weighted average cycle time formula and an example (click to enlarge).
Related post: Musings About FIFO Lane Sizing “Math”