In LEAN Times 26 back in May 2015 we spoke about how the founder of Lean, Taiicho Ohno developed his shop floor production line based on the “Supermarket” system.
Supermarkets in manufacturing are actually named after retail supermarkets, or more precisely self-service grocery stores. Before, whenever you went shopping, you told the shop-keeper what you wanted, and he or she got you the items from the back of the store, quite like many modern pharmacies.
The breakthrough in supermarkets was that the customer picked up the items themselves and paid at the check out. The company that pioneered this was Piggly Wiggly, opening its first store in Memphis in 1916, but the idea soon spread due to the savings being significantly greater than the occasional theft.
One small aspect of these supermarkets was the reordering principle. While not a completely novel concept, they simply reordered whatever quantity they sold to the customer. It is this aspect that defines modern supermarkets in manufacturing.
The first implementation of these supermarkets was by Taiichi Ohno at Toyota in 1948. Back then there were no supermarkets in Japan, but Ohno had heard about them and seen pictures taken by a classmate. Hence he named his inventories supermarkets. Only ten years later, in 1956, did Ohno visit the US, where he made sure to stop by some real retail supermarkets.
What are the requirements of a Supermarket?
A supermarket is not just any inventory. Instead, a supermarket is an inventory organised according to some rules. The three primary conditions that define a supermarket are:
1) The products are split by part type: In a supermarket, parts are stored in groups according to their part type. Ideally they are stored in physical groups, which allows easy observation of the current state (visual management). Alternatively, they could also be merely digitally arranged within a Data Management system, (Isoserve), although in this case you would need to dig through the data to see if you are running out of stock.
2) FiFo (First-in-first-out) is maintained: The first part of one type that went into the supermarket is also the first part that is taken out if that part type is required. The FiFo principle ensures that the oldest part is always used first.
3) A part leaving the supermarket gives a signal for re-production or delivery of more goods: The requirement for pull production is that any part leaving the last inventory (the supermarket) gives a signal (e.g., a kanban card) to replenish the part(s). If the supermarket is at the end of a production line, the signal is to produce more. If the supermarket is at the end of a logistic chain, the signal is to order more. Hence, it is a requirement for a functioning supermarket to give exactly such a signal. Only having a part type specific FiFo (the first two conditions) is not a supermarket, but merely a nice inventory.
Christopher Roser (AllAboutLean.com)
The Supermarket system has great relevance to us during Off-site Pre-fabrication. Alerts are used to tell us when the different phases of a project should be started and carried out, such as:
These alerts signal when it’s time to start fabrication processes. Only supplies required for each fabrication stage should be bought and only when a piece is required on site should it be delivered.
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