Building 500 units of Product A on Monday and 500 of Product B on Tuesday looks efficient — it's also exactly the pattern that overloads a plant one day and starves it the next. Volume vs. mix leveling, and the heijunka box.
Building 500 units of Product A on Monday and 500
units of Product B on Tuesday looks efficient on paper — one changeover
a day, long steady runs. It’s also exactly the pattern that overloads
a plant on Monday, starves it on Tuesday, and sends wildly uneven
demand signals up the supply chain. Heijunka is the lean tool built to
fix that.
Heijunka means production leveling: smoothing both the volume and
the mix of what’s produced so a plant runs at a steady, sustainable
pace instead of lurching between overload and idle time. It directly
targets two of the “three Ms” that lean methodology treats as root
problems — mura (unevenness) and muri (overburden) — on the theory that
unevenness in scheduling is what creates overburden on people and
equipment in the first place, not the other way around.
| Dimension | What it smooths |
|---|---|
| Volume leveling | The total quantity produced each day or shift, avoiding spikes and troughs |
| Mix leveling | The sequence of different products, building smaller amounts of each in rotation instead of large single-product batches |
A heijunka box, sometimes called a leveling box or runbox, is a
physical card-sorting tool with a grid of slots organized by time
interval down one axis and product type across the other. Production
kanban cards get placed into the box according to the leveled schedule,
giving operators a simple visual signal for what to build next without
needing to consult a computer screen or a supervisor’s verbal
instructions each time.
Mixing smaller batches of different products throughout the day only
works if changeovers between them are fast — otherwise the time lost
switching setups eats into the capacity leveling is supposed to free
up. Most successful heijunka implementations depend on quick,
well-rehearsed changeovers already in place, which is why leveling
efforts are usually built on top of, not instead of, a facility’s SMED
work.
Heijunka fits inside the lean fundamentals covered in SCMEP’s
Lean 101 Overview. As a
NIST Manufacturing Extension Partnership affiliate
serving South Carolina manufacturers since 1989, our focus is
helping teams build a leveled schedule around their actual product mix
and changeover times, not a textbook example.
If your team is dealing with uneven production loads or planning a
heijunka box implementation, you can
browse the Lean and Continuous
Improvement training catalog or email the training team.
Heijunka is a lean production leveling technique that smooths both the volume and mix of production to run at a steady, sustainable pace, rather than large single-product batches that create uneven demand and overburden.
Volume leveling smooths the total quantity produced over time to avoid spikes and troughs. Mix leveling smooths the sequence of different products, building smaller amounts of each in rotation instead of large single-product runs.
A heijunka box is a physical card-sorting tool with time-slotted grids used to visually schedule production kanban cards according to a leveled plan, giving operators a simple signal for what to build next.
Mixing smaller batches throughout the day only works if changeovers between products are fast. Without quick changeovers already in place, the time lost switching setups eats into the capacity leveling is meant to free up.
