The just-in-time (JIT) principle is an organisation and control concept used in logistics. Essentially, it means that a product is made available precisely when it is needed. However, the common understanding of the term is not altogether accurate. Although it is true that parts are only supplied when they are needed, the fundamental logic behind the concept is slightly more complex.
Thinking things through in reverse
Traditionally, production moves forward – as soon as a unit has been completed, it is delivered to the next stage in production. However, the just-in-time philosophy moves in the opposite direction to the material. Each workstation “pulls” the parts it needs from the upstream station. The required parts are only actually produced at the individual assembly stations when they are ordered. As a result, intermediary and end-products are always produced at the right place, in the right volume, to the right quality standards and only when they are required. This reduces a company’s material stock levels and minimises capital tie-up. Toyota invented and rolled out this principle in the 1950s and production output increased hugely.
The overall concept
Today, just-in-time is a logistics concept that extends beyond a company’s workshop to encompass its entire supply chain, including all suppliers and the full flow of materials and information. The Kanban system, which was derived from the JIT concept, primarily focuses on managing the flow of materials and information at workshop level.
Just-in-time in the plant
For just-in-time production to function smoothly, it is imperative that requirements and consumption are known at all times. Today, this is mostly done via electronic data capture and parts move through the production system by means of order cards (see Kanban). The individual manufacturing stages and transport need to be planned down to the smallest detail and times and quantities logged. The more flexibility there is in how materials are moved from A to B, the more efficient the system. On the one hand, when production is running smoothly, the just-in-time philosophy delivers a system that requires virtually no stockkeeping. On the other hand, minor organisational errors can have a massive impact on production, even leading to short-term stoppages.