Lean teams use heijunka to stop the peaks and troughs that create overtime, idle time and excess inventory. A steady schedule also makes pull systems and standard work stable.
Where it comes from
Heijunka is a foundation of the Toyota Production System, sitting under just-in-time and jidoka. A heijunka box is the common tool for releasing kanban in a leveled sequence.
At a glance
From weekly blocks to a leveled mix
Swipe sideways to see the whole diagram.
How to apply Heijunka
- 1
Understand demand
Analyze demand by product over several periods. Separate steady runners from low-volume or erratic items.
- 2
Calculate takt time
Divide available time by average demand. Takt sets the pace the leveled schedule must hit.
- 3
Shorten changeovers
Use SMED so the line can switch products often. Leveling mix is impractical while changeovers stay long.
- 4
Build a leveled pattern
Create a repeating sequence that mixes products in proportion to demand. Decide the pitch, or time interval, for releasing work.
- 5
Use a heijunka box
Load kanban into time slots by pitch so work is released at a steady rate. Material handlers pull one slot per interval.
- 6
Buffer and review
Hold a small finished-goods buffer to absorb short-term swings. Review the pattern when demand shifts.
Worked example
A line builds three models in weekly blocks, so stock of one model runs out while others pile up. The team cuts changeover time and moves to a daily repeating sequence in demand proportion. Inventory falls and the downstream schedule becomes predictable.
Common mistakes
- Trying to level the mix before reducing changeover times.
- Chasing every short-term order change, which reintroduces the peaks heijunka should remove.
- Leveling final assembly while upstream processes still run in large batches.
When Heijunka is not the right tool
Heijunka needs some repeat demand to level. Highly custom work with no repeating products is hard to level by mix.
A common approach is to split products into runners, repeaters and strangers, then level the runners and repeaters first.
Heijunka box and board
A heijunka box is a board with a grid of slots. Columns are time intervals, set by the pitch, and rows are products. Kanban cards are placed in the slots to show what to make in each interval, in a mixed and level sequence.
A material handler collects the cards for each interval and takes them to the line. Because the box holds the plan, everyone can see whether production is on time just by looking at which slots are empty.
Leveling volume and mix
Volume leveling makes the same total amount each day, even when orders arrive unevenly. Mix leveling spreads the different products across the day instead of in long batches.
Both need short changeovers, which is why SMED usually comes first.
Pitch and the heijunka box
Pitch is a set time unit for releasing work, often takt time multiplied by the pack quantity. A heijunka box has a slot for each pitch, holding the kanban to be released then.
Art Smalley's guide Creating Level Pull describes how leveling, pull and kanban work together.