Leveling the type and quantity of production, to reduce batching and WIP inventory and thus reduce lead time and space requirements. Additional benefits include leveling the orders placed on upstream vendors.
Assume that Products A, B and C are all produced in the same cell or production line, and demand for is 300 units per month for Product A, 200 units per month for Product B and 100 units per month for Product C.
Pure batch production would make 300 units of A, then change over to make 200 units of B then change over again to make 100 of product C.
An improvement would be to make 30 units of A, then 20 of B and 10 of C. Changeovers would have to be reduced to prevent working additional hours.
Further improvement would be to repeatedly make 3 of A then 2 of B then one of C, represented by AAABBC AAABBC AAABBC.
Heijunka would be represented by further breaking that down to ABCABA ABCABA ABCABA or even ABACAB ABACAB.
One must be mindful of realistic limits to heijunka. Changeover times have a point of diminishing return; further cost of changeover time reduction (SMED) may be justified by customer want and costs of holding, moving and storing an incremental amount of WIP inventory. Customers may not need or want delivery spread out over a period of time. Still, with the way costs of inventory compound it is best to use changeover time cost as the constraining factor, and accumulate product only in shipping if it is to be shipped by batch.