Heijunka – definition and meaning
Heijunka is a Japanese technique for achieving a perfect supply and demand balance. In other words, achieving an even output flow by carefully coordinating very small production batches across the whole manufacturing line. Heijunka means ‘leveling.’ When done correctly, it helps organizations meet demand elegantly, i.e., without haste. They meet demand while also reducing waste in the production process.
We also call this technique production smoothing or production leveling.
It is a technique for reducing the Mura which in turn reduces Muda. Mura and Muda mean ‘unevenness’ and ‘waste’ respectively.
Heijunka was crucial for the development of the smooth production efficiency in the Toyota Production System.
It is part of lean manufacturing. Lean manufacturing or lean is a systematic method of reducing waste to a minimum. However, companies achieve this without sacrificing productivity.
In an MIT presentation, Amy Reyner and Kweky Fleming described Heijunka as:
“The distribution of production volume and mix evenly over time. It converts uneven customer pull into an even and predictable manufacturing process.”
“It is generally used in combination with other key Lean principles to stabilize value flow.”
Heijunka and Just-in-Time
Heijunka is a technique to facilitate Just-in-Time (JIT) production. JIT is a manufacturing or inventory strategy in which businesses keep stock levels at a minimum.
With JIT, as orders come in, the seller contacts suppliers immediately to make immediate deliveries of components and raw materials. Just-in-Time is the opposite of Just-in-Case.
Toyota started JIT in the 1960s. People called it the Toyota Production System. By the late 1970s, Western Europe and North America had also adopted the technique.
Regarding this technique, Toyota UK’s official blog says:
“Heijunka is also important when it comes to sequencing production. For example, were the factory’s ordering system to send batches of high specification models down its assembly line at the same time, workers would be required to manage lots of complex build tasks not present in less well-equipped cars.”
With the Toyota Production System, the company assembles a mix of models within each batch. This subsequently ensures that there is a product inventory which is proportional to fluctuating demand.
The Toyota Production System used several Japanese words that manufacturers all over the world use today. For example, Kaikaku, which means ‘radical change’ in Japanese, is a drastic change approach. In other words, management tries to improve the production process by changing everything drastically.
A Heijunka box is a visual scheduling tool that people use. The box is a specific tool people use in achieving the aims of production leveling.
The box is typically a wall schedule. The schedule has a grid of boxes, i.e., rectangular receptacles or pigeon holes.
Each box column represents a specific period. Lines are drawn down the grid to break the columns in shifts, days, or even weeks.
There are also Kanban Cards in the boxes. Kanban is Japanese for ‘billboard’ or ‘signboard.’ They provide a visual representation of impending production runs.
With a Heijunka box, people can rapidly see what types of jobs are in the queue for production. It also tells them when they will occur.
To know what they have to do, workers remove the cards for the current period.
Video – Toyota: Heijunka
This Toyota Material Handling Europe video explains how the Toyota Production System works. Heijunka levels the workload. It also creates a smooth workflow.