Heijunka Box = 平準化箱 (HAY-joon-kah BOH-ku)
A Production Leveling Box, often called a Heijunka Box, is a physical grid used to sequence production in a level, mixed-model pattern. Kanban cards representing customer demand are slotted into pigeonholes by time interval and product variant, creating a visible, walking-order schedule that paces production evenly across the shift.
The box is a grid: columns represent pitch intervals across the shift; rows represent product variants. Kanban cards for each variant are dropped into the correct time slot to create a level, interleaved sequence. Every pitch, the operator or water spider pulls the cards for that interval and takes them to the line, which then produces exactly that mix.
A schedule in a computer is invisible to the operator. The physical box is at the pacemaker process, visible to everyone. The mix, the sequence and the pace are obvious in one glance. Deviations, a missing card, an empty slot, a build-up in one row, are immediately apparent and prompt investigation.
Start with the demand mix, how many of each variant the customer wants per shift. Calculate takt time and pitch. Distribute the Kanban cards for each variant evenly across the pitch intervals so that the mix in any short window matches the mix over the shift. Adjust the sequence to smooth out any changeover impacts.
The Production Leveling Box is the visual heart of Heijunka. It turns a leveled schedule from an abstract calculation into a tangible, walk-up-and-pull artifact that every operator understands. It is what makes mixed-model production sustainable at the operational level.
