Heijunka

Origin. Toyota Production System; the word means "leveling" or "smoothing."

Mechanism. Production is smoothed over time to minimize variation. Rather than producing in large batches that create peaks and troughs, produce in a mixed sequence at constant rate. Leveling reduces inventory, enables just-in-time, and stabilizes the load on upstream processes and suppliers.

Procedure. Compute the takt time: available production time divided by customer demand. Sequence production so that each product type appears at a rate matching its share of demand, interleaved rather than batched. Use a heijunka box (visual scheduling board) to assign production slots. The sequence absorbs demand variation rather than passing it upstream.

Applies to. Production scheduling, service operations, any process where demand varies and capacity is shared across multiple product types.

Limitations. Heijunka requires setup time reduction; if changeovers are slow, leveling is too expensive. It also requires stable enough demand to forecast the mix. High variability, lumpy demand, or long lead times break the model. In software, heijunka applies to work intake (limit WIP, smooth the flow of features) rather than to production.