Sizing kanban and verifying the replenishment loop

Why it matters

In a pull system, the upstream process produces in response to the consumption of the downstream process. Kanban is the production and replenishment signal that makes this authorization visible. Not every empty space is a new production order, and not every forecast may be used as if consumption had occurred. The product, the container quantity, the replenishment source and the event that creates the signal are defined together. This way the worker does not decide by personal guess what to complete and when. But preparing the card alone does not build a pull arrangement. Extra production started before consumption has occurred can exceed the limit even if a card appears on it. The behavior of the card determines more than its appearance.

To calculate the card count, the demand rate is multiplied by the replenishment time. This product gives the quantity that will be consumed until the new container returns. Replenishment time is not only the running time of the machine. Noticing the signal, waiting in the queue, setup, production, conformity inspection and moving to a usable location can all be inside the same loop. Removing a wait that falls within the scope makes the calculation look tidy but creates a shortage of containers. Adding the same wait both to the replenishment time and to a separate safety quantity without explanation can enlarge the stock limit unnecessarily. First the time boundaries are set, and then it is written down which uncertainty is covered and how.

The safety rate is a design assumption chosen for demand or replenishment variability. It cannot be said that one particular rate suits all products. The rate given in the training is accepted for the calculation; on the shop floor the choice must be justified with observation. The safety quantity does not allow producing defects or ignoring a delay. If insufficient capacity causes shortages continuously, adding more cards can only increase waiting work. As replenishment time grows, stock grows; if the queue lengthens as stock grows, cause and effect feed each other. For this reason the card calculation is assessed together with capacity and the recorded actual replenishments.

The card count is a whole number, while intermediate calculations may come out fractional. The fraction found when dividing by the container quantity is rounded up; rounding down leaves part of the calculated requirement uncovered. The quantity added by this operation is not the same as the chosen safety rate. The total authorization must also be separated from the physical full stock. Some cards may be in production, some in return, some on a full container. The same authorization must not be used twice, once in production and once on the shelf. A sound arrangement closes all card states and does not solve a lost card by automatically printing a new one. The figure, example, counterexample and short quiz numbers in this lesson are within the scope of this training. This dataset was generated synthetically for training; it does not represent a real business, employee or customer study.

Formula