Understanding lean manufacturing process is easy if the supermarket system of provisioning components for assembly is explained first.
An assembly line is provided with a supermarket of components and whatever components it requires to produce the assemblies based customer orders given to them can be taken from the supermarket. A supermarket that works with one day inventory will have enough inventory to manufacture any product from the variety it assembles up to the maximum quantity specified for a day. Thus the supermarket actually has more days of inventory for all the products summed together. But for any one product it has only a day’s inventory. The inventory is decided by the system design.
From the supermarket, as components are removed Kanbans become released for the part or component making department to produce and replenish the consumer parts. The capacity of the component making department is such that it can produce the component and keep it in stock by next day morning or actually by the end of the day so that assembly has full supermarket at its disposal the next day. One can think of a supermarket for materials for the component making department also. Thus a lean process contains supermarkets and production facilities. We can think of supermarkets in the supply chain.