Leveling the type and quantity of production over a fixed period of time. This enables production to efficiently meet customer demands while avoiding batching and results in minimum inventories, capital costs, manpower, and production lead time through the whole value stream.
With regard to level production by quantity of items, suppose that a producer routinely received orders for 500 items per week, but with significant variation by day: 200 arrive on Monday, 100 on Tuesday, 50 on Wednesday, 100 on Thursday, and 50 on Friday. To level production, the producer might place a small buffer of finished goods near shipping, to respond to Monday's high level of demand, and level production at 100 units per day through the week. By keeping a small stock of finished goods at the very end of the value stream, this producer can level demand to its plant and to its suppliers, making for more efficient utilization of assets along the entire value stream while meeting customer requirements.
With regard to leveling production by type of item, as illustrated on the next page, suppose that a shirt company offers Models A, B, C, and D to the public and that weekly demand for shirts is five of Model A, three of Model B, and two each of Models C and D. A mass producer, seeking economies of scale and wishing to minimize changeovers between products, would probably build these products in the weekly sequence A A A A A B B B C C D D.
A lean producer, mindful—in addition to the benefits outlined above—of the effect of sending large, infrequent batches of orders upstream to suppliers, would strive to build in the repeating sequence A A B C D A A B C D A B, making appropriate production system improvements, such as reducing changeover times. This sequence would be adjusted periodically according to changing customer orders.
In Japanese, the word heijunka means, roughly, "levelization."