What is heijunka?
Heijunka, or production levelling, is one of the foundations of the Toyota Production System. Customer orders arrive unevenly, but if production follows them directly, every peak ripples upstream as overtime, inventory and expediting. Heijunka levels both the volume (the same quantity every day) and the mix (every product made in every part of the day), so the whole value stream runs at a steady rhythm set by takt time.
How a heijunka box works
- The box has one row per product and one column per pitch interval (e.g. every 60 minutes).
- Each kanban represents one container of a product, and is placed in the slot of the interval when it should be made.
- At each interval, a material handler takes the cards from the next column to the pacemaker process and collects the finished containers.
- If the previous cards are not finished, the problem is visible within one interval, not at the end of the shift.
Heijunka example
A valve line has 900 minutes a day and four products with daily demand of 240, 120, 60 and 30 units: 450 units, a takt time of 120 seconds. Instead of running each product in one batch, the heijunka box places one or two V-10 kanbans (10 units each) in every one-hour column, V-20 and V-30 kanbans in most columns and a V-40 kanban every two to three hours. The load row checks that slow products do not pile up in the same hour, and the mixed-model sequence V-10, V-20, V-10, V-30… repeats through the day.
Prerequisites for levelling
- Quick changeovers: levelling multiplies changeovers; reduce them with SMED.
- Stable processes: high OEE and standard work.
- A finished-goods buffer to serve uneven orders while production stays level.
- One pacemaker process that receives the schedule; upstream processes are pulled by kanban.
How to use this Heijunka tool
- Set the time frame. Enter the available production time per day, the pitch interval (column width) and the start time.
- Add the products. For each product, enter its daily demand, units per kanban and cycle time.
- Read the box. The tool spreads each product's kanbans evenly over the intervals of the day.
- Check the load. The load row shows the work in each interval against its length; red intervals are overloaded.
- Use the sequence. The mixed-model sequence gives the repeating order of units to build at the pacemaker.
- Export. Export the heijunka box to PDF, PNG or Excel and use it to load the physical box.
Frequently asked questions
What is heijunka?
Heijunka (Japanese for "levelling") is a lean technique that levels the type and quantity of production over a fixed period. Instead of making all of product A, then all of B, a levelled line makes a little of every product in every part of the day, in a repeating mix, so that upstream processes and suppliers see a steady demand.
What is a heijunka box?
A heijunka box is a scheduling board with a row for each product and a column for each pitch interval of the day. Kanban cards placed in the slots tell the pacemaker process what to make in each interval. A material handler takes the cards out one column at a time, which also checks every interval that the line is keeping pace.
What is pitch?
Pitch is the amount of time needed to make one container (one kanban) of product: takt time × pack-out quantity. In a heijunka box, the pitch interval is the column width: the time between two withdrawals of kanbans from the box, often 15 to 60 minutes.
What is a mixed-model sequence?
A mixed-model sequence is the repeating order in which products are made, proportional to demand. With daily demand of 240 A, 120 B, 60 C and 30 D, the smallest repeating pattern has 15 units: 8 A, 4 B, 2 C and 1 D, spread as evenly as possible.
What are the benefits of production levelling?
Lower finished-goods inventory, shorter lead times, a steady workload for people and equipment, stable kanban loops and demand for suppliers, and fewer peaks of overtime. Levelling is a prerequisite for a stable pull system.
What do I need before I can level production?
Short changeovers (see SMED), because levelling means many more changeovers; a stable process with enough capacity; and finished-goods stock or a supermarket to absorb short-term demand variation while production runs to the levelled plan.