It should come as no surprise that a varying demand produces waste. By encountering peaks and valleys on the assembly line, large groups of parts are backed up and lead to downtime, idle workers, and excess inventory. The entire objective of all supply systems, led by heijunka, or work leveling, is to make sure that the assembly line produces a product in a constant, flowing manner.
The basis behind production leveling is to manufacture as small a batch as possible, so that fluctuations in demand do not affect the output very dramatically, and the production line may be given time to adapt to unexpected changes. This can be accomplished in a few ways, but one of the more prevalent ways is to set up an assembly line such that variation is accomplished inside of the line. By doing this, the same equipment will manufacture different models or different classes of products with the same machinery. Unless there is a major swing in demand that affects the entire industry, the line will be sheltered from fluctuations, more constant output will be achieved, and waste will be reduced dramatically.
Of course, heijunka cannot be made possible without the advent of modern machinery and processes that allow for one assembly line to be able to output multiple products. Henry Ford, when he revolutionized the manufacturing process, built his entire philosophy around the philosophy that an assembly line can be more efficient if one worker was able to perform their work as efficiently as possible and became an expert at one task. According to his system, this could only be accomplished by repetitive tasks that are accomplished by skilled employees repeatedly. As one can imagine, this was completely changed in the last two decades with the advent and industrialization of robots that can perform multiple tasks just as efficiently as it can a single task. This makes heijunka a much more viable possibility, as no time is lost when the production line shifts focus from one product to another.
This lean tool can be used in many situations. It does not have to be specifically geared towards manufacturing, but like most other lean tools, was created for it. Heijunka can also be used when involving paperwork reduction projects, project management, cost saving measures, and many other business related situations. Any time a company wants to streamline their processes such that an increase or reduction in demand for a product, whether that product is a service, a form, or a project output, they should be able to benefit from the process of production leveling.
The best way to demonstrate what is possible with heijunka is by illustrating with an example. A car manufacturer has 6 different car models that come out of the same plant. Up until now, there were 6 different assembly lines that put the cars together. The assembly workers were great at putting together their specific piece of the puzzle, and were always able to handle whatever was thrown their way.
About 7 years ago, demand for all cars, in general, dropped dramatically. The need for 6 assembly lines to be putting out cars is not necessary. However, in order to cut back in production, the car company had to close one of their production lines and stop making one of their models, something that they did not want to do strategically.
They employed heijunka to help them solve this problem. They closed two of their lines, and reprogrammed the other four so that they could each put out the 6 models that defined their business. This was evident when there was a large decrease in the demand for one of their models.
The company’s competitor came out with a new, more efficient model that is comparable to one of the models the company puts out. The senior leadership knew that demand for their model would be dramatically reduced, so they started producing less of that model. All they had to do in order to accomplish that was to tell the assembly line to skip that model every fifth time it came around. Their production of that one model was reduced by 20% and the production of the other 6 models was unaffected. They were able to immediately react to the shift in demand, one of heijunka’s end goals.