Cell Validation and Flexible Capacity

Why it matters

When demand changes, changing the number of workers in the cell can be useful; but deleting one person from the same task schedule does not create a new work sequence. The remaining workers walk to different points, combine some tasks and start the automatic processes at different moments. Task handovers may decrease; on the other hand, walking or waiting may increase. For this reason the one-, two- and three-worker arrangements are defined as separate methods. Each arrangement has its own person loads, machine times and part positions. Flexibility is not getting the same efficiency with any number of workers; it is being able to switch between validated options that fit the changing demand. The worker's task knowledge is part of this option too.

Changing capacity in proportion to the number of people misses the joint limit of the human and the machine. In an arrangement where human work dominates, an additional person can reduce the output interval. Once the machine limit is reached, adding a new person does not make the same resource process faster. When the number of workers decreases and new walking or process waiting appears, the drop in rate may not be exactly proportional either. Capacity forms separate steps like a staircase; each step rests on a specific work sequence and set of constraints. Different distributions with the same number of workers can give different results. So the unit of comparison is not only the number of people but the verified output interval of the defined arrangement.

Validation means showing that the output expected by calculation is achieved in repeated work and that the product stays suitable. Choosing only the shortest cycle can hide normal variation and support jobs. Starting conditions, the quantity of parts in the cell, the replenishment arrangement and the workers' skills are part of the same record. Nonconforming or incomplete products are not counted as evidence of capacity. Even if an arrangement works in a short trial, its daily capacity is different if it stops during regular container changes. The learning period and the settled working period are evaluated separately. A numerical result gains meaning for a decision when it is explained under which conditions it was obtained; a single daily total does not show all the causes.

The transition between worker arrangements also takes time and attention. While the task sharing changes, the position of work in process, completed operations and the restart sequence must be determined. The time in this transition that cannot be given to production is subtracted from the available time of the changeover day. The same loss is not added again to the cycle time. A flexible capacity decision, besides meeting today's demand, also states under which change a retrial is needed. A new product, a different machine time or a missing skill can invalidate the old capacity step. The aim is not to work with the fewest people in every situation, but to choose the smallest verified arrangement that meets the given demand safely and with suitable product.

Formula