Heijunka is an essential practice of the Toyota Production System to maintain a stable and efficient production. It’s goal is to produce goods at a constant rate so that further processing may also be carried out at a constant and predictable rate. This prevents stress on the system and employees with variable demand. A fitting mantra would be, “keep calm and heijunka on”.
To prevent fluctuations in production, it essential to also minimize fluctuation in the final assembly line. Toyota’s final assembly line never assembles the same automobile model in a batch. Instead, they level production by assembling a mix of models in each batch and the batches are made as small as possible.
Heijunka controls production to help deliver exactly what the customer wants, when they want it. This naturally lends itself to being green as it helps prevent muda waste, in turn resulting in less energy, natural resources, landfill waste, and an attitude of apathy toward overproduction. Even more interesting though, is how the concept of heijunka itself is found in nature. Ecosystems have perfected a heijunka model over the course of evolution. We may think that “batch thinking” is second nature to us, but in reality, nature has already figured out how to balance efficiency with resilience to survive.
Significant research has explored this practice and was published in two inter-disciplinary papers. The papers explain how alligators received amounts carbon transfer from being on the top of the food chain. The alligator’s main prey, large fish, turtles and snakes, consume prawns which have high rates of carbon transfer, and are therefore highly nutritious. The large fish are the most efficient of the three as they have the highest rate of carbon transfer from prawns. If nature thought in “batches” or maximizing efficiency, alligators would have evolved to feed solely on large fish, however, the species has thrived on a more diversified diet.
Diversity gives the reptiles the advantage of flexibility: should the population of large fish suddenly reduce drastically, they can rely on their other sources of food to survive. It’s easy to draw a parallel to lean manufacturing, where having a mix of products in production hedges against the inability to survive an increase or decrease in demand.
Examples of heijunka in nature are easily found. For example, the circulatory system in our bodies has a network of large arteries and veins which descend into a large network of capillaries. Likewise our lungs split from the main trachea to further crack into the bronchi, themselves dividing into bronchioles. Trees and other plants work this way as well, beginning from the trunk, to branches of decreasing sizes, ending as a multitude of leaves. When a similar pattern repeats across various scales, it’s called a fractal. This design can be found in the building blocks of our DNA sequence.
Nature has been working on production for millions of years. A possible reason why Lean has seen such dramatic results could be due to its common sense, biomimetic systems. In nature, and as we can see in business, the systems that stay around the longest are the ones that leverage a diversity of scales building in efficiency and resilience.
Ulanowicz, R.E., Goerner, S.J., Lieater, B., Gomez, R., Quantifying sustainability: resilience, efficiency and the return of information theory. Ecological Complexity 6 (2009), 27–36
Goerner, S.J., Lieater, B., Ulanowicz, R.E., Quantifying sustainability: resilience, efficiency and the return of information theory. Ecological Economics 69 (2009) 76–81