Also called production levelling, level loading, heijunka box
What is heijunka?
Smoothing the production schedule so the plant makes a steady mix every day instead of lurching between big batches.
What else it is called
- Other names
- production levelling, level loading, heijunka box
- In French
- lissage de la production
Related entries
Understanding heijunka
Rather than making a month of product A then a month of product B, a levelled schedule makes some of each every day in roughly the proportion the customer buys them. The plant runs at a steady rate, the staffing is predictable, and supplier deliveries can be regular instead of feast and famine.
The obstacle is changeover time. A plant that loses four hours to a changeover cannot afford to do three a day, so it runs long batches, which creates the unevenness it then has to manage with inventory and overtime. This is why changeover reduction and levelling nearly always have to be tackled together, and why levelling fails when it is attempted on its own.
In practice
Compare your weekly overtime hours across a quarter. If they swing wildly, the schedule is doing that to you, and the cost is being paid in premium labour and in supplier goodwill.
Frequently asked
How can we level when our customers order unevenly?
You level what you make, not what they order, and hold a small finished goods buffer on the regular items to absorb the difference. For genuinely irregular products, level the predictable base and schedule the rest around it.