Leveling box

A tool used to level the mix and volume of production by distributing kanban at fixed intervals within a facility. Also called heijunka-box. 

The illustration shows a typical leveling box. Each horizontal row relates to one type of product (one part number). Each vertical column represents identical intervals for rhythmic kanban dispensing. The shift starts at 7:00 a.m. and the interval for kanban dispensing is always twenty minutes. This is the frequency at which the material worker removes kanban from the box and issues it to production processes within the facility. 

While the boxes represent the timing of material flow and information flow, the kanban in the boxes each represent one production pitch for one product type. (Pitch is the branch time multiplied by the package size). In the case of product A, the pitch is 20 minutes and there is one kanban in the box for each time interval. For product B, however, the pitch is 10 minutes, so in that case two kanban are in each box. Product C has a pitch of 40 minutes, so there the kanban are located around the box. Products D and E share a production process with a 20-minute pitch and a demand ratio for product D versus product E of 2:1. Therefore, there is a kanban for product D in the first two intervals of the shift and a kanban for product E in the third interval, and so it continues in the same order. 

When the leveling box is used in this way, it consistently levels demand by always working with short units of time (rather than issuing demand for a shift, day or week) and also levels demand by product within the mix (for example, by ensuring that product D and E are produced in a stable ratio and in small batches).