When we look at the flow, where do you see?
One of the most essential places to see is the flow's division and confluence points.
Water flow has long attracted humans' attention, which was necessary for us to develop agriculture. In hydrology, there are studies on the confluence of the water flow. One study discusses the six zones that appear when the flows merge. Those zones are;
🔹 Stagnation zone
🔹 Deflection zone
🔹 Recirculation zone
🔹 Maximum velocity zone
🔹 Recovery zone
🔹 Shear layers
Looking at these zones, we recognize that we have something similar to material and information flow in operations.
🔹 Stagnation zone = Inventory
🔹 Deflection zone = Adjustments
🔹 Recirculation zone = Rejects, return, rework
🔹 Maximum velocity zone = Typically, we talk about “Lead time” based on this
🔹 Recovery zone = Processes after confluence that will be impacted
🔹 Shear layers = Confusions
Of course, it is not precisely the same, but some are similar. In the flow of operations, things could go even worse. For example, the Stagnation zone might be right in the center of the shop floor, with materials and people moving around it. It’s been like that for years, and nobody questions why it is there. Mother Nature is more logical about why and where we have stagnation zones.
Identifying the flow's division and confluence points is the most critical step. Unfortunately, some believe in ignoring them. “It’s too complicated to draw,” a manager responded sarcastically when we asked about these questions. My coach responded, “If so, stop blaming people for not having discipline. You are giving them a chaotic flow.” People working on the genba are often blamed for the chaos at these points. But there is no mechanism in place to control the flow. Without such control, it is unfair to blame the discipline. There is a good reason why the 5S goes wrong in such places, or people do not follow the standards.
Here are places where we have division and confluence.
1️⃣ Difference in the number of processes
When the number of processes differs, it automatically creates some division or confluence. The only situation that doesn’t have these points is one by one.
Suppose there is a sequence of processes from A to B. When the quantity relationship is A < B, this will be a division. When the relationship is A > B, this will be confluence.
The actual number of processes will have a significant impact. For example, flowing from one to two will be much simpler than flowing from one to three. Also, from two to three is simpler than flowing from three to four. Identifying each point of the process and drawing the lines between them is critically important because differences in such structures require different mechanisms.
Another sub-category of this is the difference in the process's batch size. We often mix the processes one by one with other batch quantities or rules, which creates similar turbulences.
2️⃣ Capacity
Another important aspect is to consider each process's capacity. The above example assumes that all processes have the same capacity.
When we have different capacities, then the difference must be considered. Here, we are not talking about operational availability but the theoretical capacity. When one process has a low operational availability, that is the problem. We must immediately work on problem-solving. We should always design a flow based on high operational availability.
Capacity difference creates complexity in flow. Suppose there is a confluence of three processes into one, and one has double the capacity of the other processes. Then, we must create a Heijyunka mechanism that allows the process to pull considering the capacity. The sequence will be like “ABAC.” This way, we will consistently pull from the suitable machine. If not, such confluence will become chaotic.
3️⃣ Reverse
Reverse is a condition in which processes inside a flow are not always in the same sequence. Some products flow from A to B, but others go from B to A.
In many cases, there is no logical reason why it has reversed. It is like a designer or engineer's personal preference. In such cases, it is better to standardize the flow sequence. Yet, in some cases, such a reverse exists.
Reverse division and confluence should be handled with the utmost awareness. Such processes are hazardous and can result in quality issues or process skips. Confusion happens frequently, and inventory could flood the area.
Every division and confluence requires a specific mechanism to control the flow. The control mechanism is particular to the division and confluence's structure. Before copying the mechanism, many must understand the structure or relationships among the processes. Wrong mechanisms will do more harm than good.
The foundation of TPS is eliminating such divisions and confluences. “One by one” challenges the difference in the number of processes. “Line balance” thinking challenges the differences in the capacity. “Standardized work” challenges to keep one sequence. The ideal is to eliminate these points physically. The worst crime is pretending these points don’t exist on paper. We must create a unique, controlling mechanism if we can’t eliminate these points. However, the mechanism should highlight the problem when there is one. Simply keeping more inventory is not the right approach since it will hide the issues of the flow.
The division and confluence of the flow are critically important. Please don’t ignore them.🙏