Just-in-time (JIT) manufacturing is a production model in which items are created to meet demand, not created in surplus or in advance of need. The purpose of JIT production is to avoid the waste associated with overproduction, waiting and excess inventory, three of the seven waste categories defined in the Toyota Production System (known in North America as the lean production model).
The JIT concept was described by Henry Ford in his 1923 book, My Life and Work:
We have found in buying materials that it is not worthwhile to buy for other than immediate needs. We buy only enough to fit into the plan of production, taking into consideration the state of transportation at the time. If transportation were perfect and an even flow of materials could be assured, it would not be necessary to carry any stock whatsoever. The carloads of raw materials would arrive on schedule and in the planned order and amounts, and go from the railway cars into production. That would save a great deal of money, for it would give a very rapid turnover and thus decrease the amount of money tied up in materials.
Toyota adopted JIT in the Toyota Production System (TPS), as a means of eliminating the seven wastes. However, it was not at the Ford Motor Company that Toyota representatives saw the JIT model in action. When Toyota toured plants in the United States in 1956, Ford had not yet fully implemented the JIT model. It was at Piggly Wiggly, the first self-service grocery chain, that Toyota representatives saw JIT demonstrated and that was the model they based their system on.
In the major alternative to JIT manufacturing, inventory in excess of immediate need is managed. That model is sometimes referred to as "just-in-case" (JIC) manufacturing.
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Wikipedia has more information about JIT manufacturing.
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