Leveling the type and amount of production over a fixed period of time, allowing production to efficiently meet customer requirements.
Batch formation is avoided and inventories, capital costs, manpower and production lead time are minimized throughout the value stream.
When leveling the quantity of production, imagine that a producer routinely receives orders for 500 items per week, but with considerable variation each day: on Monday an order for 200 items arrives, on Tuesday one for 100, on Wednesday one for 50, on Thursday one for 100 and on Friday one for
50. To level out production, the producer could ensure that there is a small buffer of finished goods ready for delivery. That way he can adequately respond to Monday's high demand and keep daily production at 100 throughout the week. By keeping a small amount of finished goods in stock at the very end of the value stream, this producer can level the demand for his plant and his suppliers, making more efficient use of his assets throughout the value stream and responding appropriately to customer demand.
When leveling the type of product (see also illustration page 35), imagine that a company making T-shirts offers models A, B, C and D to the public and that the weekly demand for T-shirts is five of model A, three of model B and two each of models C and D. A mass producer, trying to achieve economies of scale and minimize changeovers, would probably produce these products in the weekly order AAAAABABBBCCDD.
A Lean manufacturer, realizing what happens when it sends large, infrequent orders to suppliers, would strive to incorporate the repeating sequence AABCDAABCDAB and make matching improvements to the production system, such as reduction of changeover times. Depending on changing customer orders, this sequence would be adjusted periodically.
In Japanese, the word heijunka roughly means 'equalization'.