Weighted average cycle time (Tcwa), also known as “average weighted cycle time,” provides a representative average cycle time (Tc) within a mixed model environment. 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 Tc‘s vary.
Tcwa can be calculated for operator cycle times, machine cycle times and effective machine cycle times. Often Tcwa is presumed to be operator related, but this is not always the case.
As we endeavor to maintain a Tc that is less than or, at most, equal to takt time (Tt), mixed models and their varying work content will likely have Tc‘s for some products or services that are below Tt, while others exceed Tt. Tcwa serves as an average proxy for Tc and can be the same as planned cycle time.
Clearly, change in product or service mix will change Tcwa. As the demand mix shifts to one with a greater proportion of Tc(s) that exceed the average, then Tcwa will approach and may exceed Tt. 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.
The math follows.