What does Heijunka (平準化) mean?

Heijunka is Japanese for “leveling” or “smoothing”: the deliberate spreading of production to maintain a constant and predictable rhythm—in both quantity and product type—over a fixed period of time. Heijunka is not a reaction to customer demand, but a deliberate buffer between the volatility of the market and the stability required by an efficient production system.

Without leveling, irregular demand amplifies as it moves upstream through the value stream: small fluctuations at the end become larger fluctuations for suppliers, leading to overproduction, inventory buffers, capacity issues, and waste. Heijunka mitigates this effect by maintaining a small, controlled buffer of finished products at the end of the value stream and feeding a steady production flow from there.

Quantity Smoothing
‍Supposea manufacturer delivers 500 items per week, but daily orders vary widely: 200 on Monday, 100 on Tuesday, 50 on Wednesday, 100 on Thursday, and 50 on Friday. Instead of responding to current demand every day, the manufacturer maintains a small buffer of finished products and produces a constant 100 units every day. The buffer absorbs the daily fluctuations. The result: a more stable workload for the factory and for the suppliers.

-style leveling ‍Supposea T-shirt manufacturer offers four models with the following weekly demand: five of model A, three of model B, and two each of models C and D. A mass producer would manufacture in the order AAAAABBBCCDD—large batches per model to minimize changeovers. A Lean aims for a repeating mixed sequence such as AABCDAABCDAB, which reflects the actual demand ratio and prevents large, irregular orders to suppliers. This does, however, require short changeover times—heijunka and SMED are inextricably linked in that regard.

The Heijunka Box
‍Inpractice, Heijunka is often supported by a Heijunka box: a physical planning tool divided into time periods (usually equal to the pitch, a multiple of the takt time) in which kanbans are placed to define the production plan for each period. The heijunka box makes the planned production mix visually apparent and helps maintain a steady rhythm in production.

Together with just-in-time and standardized work, heijunka forms the operational foundation for a stable and responsive production system.

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