Future state value stream map: flow, pull and kanban

Why it matters

A future state map is not prepared by erasing every queue on the current map. First the customer's demand, the rhythm of the flow and the workable operating conditions of the resources are determined. Then it is chosen which processes can be connected without unnecessary waiting between them. If the process sequence, quality assurance, safe access and capacity are not suitable, merging two boxes in the drawing does not create continuous flow. Where the flow cannot be connected, it is defined clearly how long material may wait and with what information production will start. In this way the future state stops being merely a layout picture and becomes a proposal that arranges material movement and the production decision together. Every connection of this proposal must rest on current data and a testable condition.

In pull, the earlier process replenishes, in a set quantity, the realized consumption of the next process. Kanban is the signal used for production or replenishment. The signal states which part is to be replenished, in what quantity and between which points. The consumption of one container produces authorization only for that part and the defined container quantity. A resource left idle producing the product it prefers does not fit this rule. In limited part stock, called a supermarket, a quantity can be held for specific products. A first-in-first-out lane, on the other hand, preserves the sequence of the products and lets them wait up to a certain upper limit. In both solutions, what the earlier process will do when the limit is full must be defined. A limit that exists only in a report does not provide control in practice.

The replenishment time on which the card calculation rests is not only the machine's processing time. The interval is taken from the moment the consumption signal arises until the replenished full container is available for the consumer. Signal transmission, job sequence, setup, production, inspection and transport can be in this interval. A card count calculated with an incomplete time may fall short. The safety allowance is not used to hide this shortcoming; it is an explicit assumption against defined variability. The demand rate and the replenishment time must be on the same time basis. Multiplying daily demand directly by a time in hours is a unit error. The container size must also describe the actual usable product quantity; if there is short filling, the validity of the nominal quantity is verified separately.

In this module the aim is to choose the boundary of the future state and to verify the logic of the card calculation. The detailed setup of the real stock and card arrangement is covered in later modules. Here it is explained which material will be tied to flow and which to limited replenishment. The most important limit is this: fewer cards does not mean more production capacity. If capacity is below demand, reducing the card count does not close the gap. More cards also do not permanently make an insufficient producer sufficient. The proposal is tested together with stock quantity, lead time, good-product output and safety conditions. Announcing only a target card count without writing who will examine which data when a problem arises is an incomplete design.

Formula