Heijunka

In today’s world, many manufacturing or business companies are consistently working towards completely incorporating Lean manufacturing or one-piece process flow as a management practice. In essence, they want to be able to produce goods and services just as requested by customer when they want them.  However, what often visible around is what you could describe as a “hurry up, then slow down” build-to-order approach to manufacturing. This is because orders for products and services vary from time to time, thereby creating uneven production scheduling.  

Companies who produce items first with the hope that customers will come placing orders will usually have huge quantities piling while paying overtime and stressing their people and equipment one week at the same time. It becomes even worse when some workers are forced to leave as a result of low number of orders over time. With this, what happens as a result is that large amounts of inventory will be left without customers who want them, poor product and services quality as a result and other hidden problems. In order to fight off the issue, the management of Toyota Car Company came up with a concept which they called heijunka, levelling out the work schedule.

Heijunka (otherwise known as Production Levelling or Production Smoothing) is a Japanese word used to describe the technique dedicated to reducing the mura (a Japanese word meaning unevenness, inconsistency in physical matter or human spiritual condition in English) waste. Heijunka was vital to the development of production efficiency in the Toyota Production System and has been proven to work for other companies and organisation as well who are interested in practicing Lean Manufacturing. Basically, the idea is to produce intermediate goods at a constant rate, to allow further processing to be carried out at a constant and predictable rate.

Heijunka, as a management technique, is more often encountered in the manufacturing environment. For example, assuming a factory can switch over their machines in a convenient manner (a step which is a precondition for heijunka) a levelled production system may look something close to the example below: 

• XXX (c) YY (c) Z (c) XXX (c) YY (c) Z (c) XXX (c) YY (c) Z – where (c) stands for changeover.

However, when compare to how a mass producing company would likely approach this same product demand structure, the result could turn out to be something like that shown below; but bear in mind that their changeover time is likely much greater when compared to the lean producer’s.

• XXXXXXXXX (c) XXXXXX (c) ZZZ

Based on these and in addition to the above definition, Lean Lexicon – Third Edition describes Heijunka as: “Levelling the type and quantity of production over a fixed period of time.  This enables production to efficiently meet customers’ demands while avoiding batching and results in minimum inventories, capital costs, manpower, and production lead time through the whole value stream”.
Ideally, Heijunka or levelled production can easily be achieved where demand is constant but in the real world where actual customer demand appears to fluctuate from time to time, two approaches could be adopted in lean: Demand levelling and production levelling through flexible production.