One of the methods put into place by Toyota Manufacturing in Japan many years ago, is called Heijunka. This is a Japanese word meaning ‘leveling’. The Toyota Production System is the basis for Lean Manufacturing, which focuses on increasing efficiency and reducing waste in manufacturing.
Heijunka is used to smooth out unpredictable customer demand and is often referred to as Production Leveling. By reducing the Mura (unevenness), manufacturing companies can usually better manage and reduce Muda (waste), which is often key to developing and sustaining efficient and stable manufacturing models.
One of the tools used in Lean Manufacturing concerning Heijunka, is called a Heijunka Box. This particular implement is used to obtain the goal of Heijunka, which is ultimately an undisturbed production flow.
In a nutshell, a Heijunka Box is a visual device that can come in various shapes and designs. Most commonly, it is seen as a working diagram detailing the production schedule, including different types of product, over the course of a period of time. This period of time can vary case by case, but is typically a week of production.
This matrix can be a board, a wheel, or even an actual structure. It is divided up into rows and columns. Most often, the columns are of the specified work interval in hours or days, while the rows detail various product types.
This method of staging production allows the responsible party to evenly and efficiently distribute information to various manufacturing processes throughout the plant. The quantities posted in each slot are governed by the takt time (required time to produce a finished product to meet customer demand). This is referred to as the ‘pitch’ in regard to the Heijunka Box.
Utilizing this strategy, overall production is consistently leveled and streamlined by ensuring steady and reliable production of each product type. This is in opposition to what is commonly seen in manufacturing where production quantities for the day or week are released to the shop in advance, all at once. This brings up another important aspect of the Heijunka Box, which is the data included in the slots themselves.
In conjunction with this tool, another Lean Manufacturing tool called a Kanban Card is also used. These cards are basically a visual depiction of a production item. Ideally, it should contain all relevant and important information regarding the processes, personnel, and time lines necessary to deliver to the customer on time.
To be successful using these methodologies, it is critically important everybody is on the same page and accountable for their actions. If nobody follows the rules and direction, it will become nearly impossible to sustain for any duration that shows a positive improvement to overall production. For these reasons, and for the ease of future training, a number of companies today are moving toward storing the Kanban Cards online.
Hopefully, the information provided here has been enough to spark your curiosity and point out just a few of the benefits of Lean Manufacturing, and specifically the advantage of Production Leveling using a Heijunka Box.