Just in time (JIT)
This time we will reflect on and discuss JIT, one of the two pillars of the TPS house.
This pillar has everything to do with the production side of the system.
Its creator was Kiichiro Toyoda, the founder of Toyota. From the start of operations, one of the things he observed was that finished parts sat in storage waiting until they were needed for the next stage of production.
The parts were exposed and could easily be damaged and rendered useless. Large factories usually have enormous spaces and resources to store parts in warehouses. Toyota did not, and Kiichiro saw that this was waste.
Capital saved on inventory and warehouse space could be used for something else. At that moment a new production philosophy was born, called “just-in-time”. And what Kiichiro told employees was: no component of a car should be made before it is needed. In other words, components must be made “just-in-time”.
JIT means producing and transporting what is needed, when it is needed, in the exact quantity needed.
It aims at manufacturing with no or minimal work-in-process inventory, resulting in a very short lead time with enormous cost savings. It benefits quality and also promotes employee motivation.
Let us consider the case of a conventional production system. Many parts and components needed for assembly must be scheduled to be at the right place in the production process (across several processes) in time for assembly of the right model. The detailed schedule must be planned months in advance, distributed to suppliers, and production must proceed accordingly.
In practice it is very difficult for things to happen as planned. The conditions at the time the plan was first established and at the time production is carried out can change drastically.
Even without taking changes into account, it is a huge and difficult task to coordinate hundreds of models and thousands of parts and components at the same time, not to mention the countless problems that will arise during the assembly process. The predictable consequences of facing this situation are increased inventory of parts and components and a longer production lead time.
JIT production avoids all these problems by strictly observing the following three principles:
- Takt time: knowing in detail the required volume (what, when and at what speed it must be produced),
- Pull production: a single flow of information (kanban)
- Flow production: continuous flow process (general rule – one-piece flow)
Takt time and continuous flow production reduce production lead time, ensured by synchronized processing across all manufacturing processes.
Pull production, carried out through the use of kanban, is the control mechanism that prevents overproduction and ensures fast and accurate dissemination of information.
The three principles above have a necessary precondition for them to work effectively: heijunka, or leveled production.
I recommend taking another look at the article on Heijunka already published in this column, as well as the article on takt time.
In the next articles I will discuss Flow production and Pull production in separate chapters. Stay tuned.
