Section 4. Construction of the Automotive Department Assembly Plant and Koromo Plant
Item 5. The Origins of Just-in-Time
Kiichiro Toyoda proposed Just-in-Time production when operations began at the Koromo Plant. This was the beginning of Just-in-Time used in the current Toyota Production System.
I believe that the most important thing is to ensure that there is neither shortage nor excess, that is, to ensure that there is no excess labor and time for the designated production. There is no waste and there is no excess. It means not having to wait for parts to be circulated around. For Just-in-Time, it is important that each part be ready 'just in time'. This is the first principle of increasing efficiency.1
Eiji Toyoda, who was instructed by Kiichiro at that time, explained the Just-in-Time concept in the following manner:
What Kiichiro had in mind was to produce the needed quantity of the required parts each day. To make this a reality, every single step of the operation, like it or not, had to be converted over to his flow production system. Kiichiro referred to this as the 'just-in-time' concept. By this he meant: 'Just make what is needed in time, but don't make too much.2
According to the recollections of Jiro Iwaoka, who was in charge of the machine shop at the Koromo Plant, Kiichiro "was using the slogan 'Just-in-Time' even before we shifted production to the Koromo Plant".3
When operations started at the Koromo Plant, a Preparation Office was established between the raw blank divisions and machining divisions and an early-stage production system was adopted before the transition to Just-in-Time production. The Preparation Office delivered only the raw blanks necessary for that day's planned production to the Machining Shop, the Machining Shop delivered completed parts corresponding to the raw blanks that it received to the Assembly Shop, and the Assembly Shop produced only that number of complete vehicles. When the planned quantity was manufactured and delivered to the next process, that department shut down its line. Kiichiro proposed a revolutionary management system that did not use transfer slips, but it took a long time for the ideas to be understood.4
As a result, for the time being, the Goguchi production control system (discussed below) was used for production management. Regulation was tightened during wartime, and a rationing system was implemented for automobile production materials in 1939, making it impossible to acquire just the necessary materials in just the necessary volumes, and just when they were necessary. Later, Just-in-Time production initiatives were unavoidably suspended.
The Just-in-Time concept was not fully realized until 1954 when the ‘supermarket method’ was proposed. This was the idea of having subsequent processes take what they need from the earlier processes. The kanban was proposed as a tool for carrying this out, and it is referred to as the ‘Kanban system’.
The name has undergone various transformations, but the fundamental concept of Just-in-Time remains the same, and with the concept of jidoka (‘automation with a human touch’), it is one of the two core elements of the Toyota Production System.