“Flow.” One of the core concepts of the Toyota Production System. Today, I would like to try some analysis on this.
In a dictionary, there are many definitions of flow. Many are associated with movement. Unfortunately, in TPS, we will not be able to use those definitions because we have the waste of movement and transportation. To satisfy the elimination of these two wastes, I would like to define flow as “continuous value-adding processes.” The opposite of flow is stock. Inventory is also a waste. For a long time, I thought the waste of inventory is worse than movement or transportation. But after observing materials just moving on overhead conveyors or trucks for hours, creating fake flow mode, I don’t know which is more criminal.
Flow is one word in English, but there are two words as the translation of “Flow” in Japanese. Below are those words and a simple explanation.
- Nagare （流れ）= flow without intention. Ex. Water flows through a river.
- Nagashi （流し）= Flow with intention. Ex. I flow water into a tank.
It is a very annoying difference, but we use both in TPS. “Flow production” will be “Nagare” since we are producing according to flow. For “One-piece flow,” we use “Nagashi” because we are intentionally making one at a time. Very often, a TPS coach will ask this question, “Is this Nagare or Nagashi?” The meaning behind this question is, what is the intention? Or another way to think about this is the lead time. In Nagare, we have to add words like “about,” “probably,” “average,” etc., in front of the lead time. In Nagashi, lead time is a specific number.
Crucial points in Flow for TPS are mergers and split points. Unfortunately, at these points, we often have problems, problems about quality, sequence, inventory, etc. The ideal is to eliminate such points and create one large continuous flow. Flow without such mergers and split points are called “organized flow （整流）.” The opposite of this is the “contaminated flow（濁流）.” If we have to keep the mergers and split points, these points will require additional control. This control has to be something physical that moves according to the material, not virtual. Also, in some technics, they ignore the mergers and split points on the paper. Such technic is not TPS. Very often, when my father saw such a report, he will say, “if the flow is this simple, why we don’t make the shop floor simple right now.”
The flow needs to be standardized work-friendly. Standardized work-friendly means is that the flow needs be able to adjust according to changes in demand. For example, inside a flow, we can have two kinds of processes, manual and automatic. If these two methods stay next to each other in a flow, it becomes challenging to re-balance the flow when the demand changes. So it better to separate them. The main flow will contain only the manual processes, and the automatic form a loop from the main flow. Also, all processes inside a flow should be in one direction, counterclockwise. If a different direction of work is inside, this will cause a massive hiccup in the flow.
Ideally, a flow should report to a manager. Flow management means that the manager needs to be capable of managing many different functionalities. A multi-functional manager might sound like a daunting task. But today, the plant manager is the only multi-functional manager. Is this person handling every multi-functional issue? Most likely, no. Instead, having flow and flow managers means having mini-plants inside a plant. Organizations can solve so many multi-functional problems by having this concept.
Flow. Such an important topic that is understudied. I hope this blog sorted some information.