Production leveling, also known as production smoothing or – by its Japanese original term – heijunka (平準化), is a technique for reducing the mura (unevenness) which in turn reduces muda (waste). It was vital to the development of production efficiency in the Toyota Production System and lean manufacturing. The goal is to produce intermediate goods at a constant rate so that further processing may also be carried out at a constant and predictable rate.
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Where demand is constant, production leveling is easy, but where customer demand fluctuates, two approaches have been adopted: 1) demand leveling and 2) production leveling through flexible production.
To prevent fluctuations in production, even in outside affiliates, it is important to minimize fluctuation in the final assembly line. Toyota's final assembly line never assembles the same automobile model in a batch. Instead, they level production by assembling a mix of models in each batch and the batches are made as small as possible.