Standard In-process stock

Standard In-process stock is one of the three elements of standardized work. It is essential to maintain the repeatability of work and separate human and machine tasks within standardized work.

In Japanese, at Toyota, this is called “Temochi.” 【手持ち】 Many other Japanese have used the phrase Zaiko 【在庫】, which directly means stock. We explained that both mean the same, but there are some nuances.

“Temochi” comes from “Te【手】,” which means Hand, and “Mochi【持ち】,” which means to hold. So, the direct translation is “Hold by hand.” For example, when we play cards, the cards that the player has in their hands are “Temochi.”

From such original meaning, for the daily life of the Japanese, “Temochi” meant “Cash on hand.” A real-life conversation might go: “Do you want to go out and drink?” “No, my Temochi is tight today.” (Very real example.) Understanding the connection between cash and “Temochi” within the Toyota Production System reveals another concept related to money, known as Kanban. “Treat the Kanban like cash.” But Kanban represents outgoing cash. We don’t want to overspend, so we manage it with Kanban. If Kanban represents the cash going out, then the cash that keeps our standardized work circulating is known as “Standard Temochi.” Without such funds, our daily lives would come to a halt, and we would suffer. Therefore, it is the minimum amount of cash that we need to keep on hand to live a daily life. And, Ohno explained it as “the minimum intra-process work in-process needed.” Many places continuously run out of “Standard In-process stock” and suffer even more when trying to recover from downtime or the start of a shift. “One process is down, but let's keep the other processes running.” Supply processes leave early before the shift ends, emptying the whole line. After such actions, production will require time and effort to recover. The opposite condition exists when we have extra “Temochi.” The Japanese will say “Asobi,” which means to play. A real-life example would be, “I have extra Temochi today, so let’s go and drink.”

Therefore, “Temochi” is the minimum required stock to keep the standardized work in action. This quality is not based on opinion; it is based on strict rules.

The rules are straightforward.

1️⃣ When we have Jidou-ka and man and machine work are separated, we need a standard in-process stock. The quantity of standard in-process stock varies depending on the machine.

2️⃣ When the operator works in reverse of the process flow, we need the standard in-process stock.

These two are the only cases where we will require the standard in-process stock.

One common mistake is placing in-process stock between processes. Ohno is clear on this point. “Standard inventory between processes is generally unnecessary if work is carried out in the order of the machining processes.” (Ohno, Taiichi. Toyota Production System: Beyond Large-Scale Production (p. 23).) Unfortunately, despite his clear teaching, many people want to place some inventory due to instability. Such stock masks fluctuations and undermines the need to address the underlying causes.

The worst-case scenario of the above occurs when those who consider safety stock standard also include it as in-process stock. I even met some “Lean” folks who rush to add safety stock without addressing the root cause of the problem. Safety stock is not part of the standardized work. Standardized work does not deal with problems; it highlights them. If a problem arises and standardized work can’t be followed, we should immediately stop and start problem-solving.

Final point. We say, “Standardized work” and “Standard In-process stock.” It is “Standardzid work” because we continue to change and improve. It is “Standard In-process stock” as we define it based on the rules.