Guideline #3: Use supermarkets to control production where continuous flow does not extend upstream
There are often spots in the Value stream where continuous flow is not possible and batching is necessary. There are several reasons for this including:
There are several icons associated with a supermarket pull system:
The supermarket icon is open on the left side, which faces the supplying process. This is because this supermarket “belongs” to the supplying process and is used to schedule that process. On the factory floor, supermarkets should ordinarily be located near the supplying process to help that process maintain a visual sense of customer usage and requirements. The “customer” process material handler then comes to the supplier’s supermarket and withdraws what is needed. These withdraws trigger the movement of pre-printed kanban (typically cards) from the supermarket to the supplier process, where they are used as the only production instruction for that process.
Pull systems are a nice way to control production between processes that cannot be tied together in a continuous flow, but sometimes it is not piratical to keep and inventory of all possible part variations in a pull-system supermarket. Examples include custom parts, parts that have a short shelf life, and costly parts that are used infrequently. In some of these cases you can use a FIFO (“first-in-first-out”) lane between two decoupled processes to substitute for a supermarket and maintain a flow between them. Think of a FIFO lane like a chute that con hold only a certain amount of inventory, with the supplying process at the chute entrance and the customer process at the exit. If the FIFO lane gets full, the supplying process must stop producing until the customer has used up some of the inventory.