A critical element to the Toyota Production System and Lean manufacturing is Heijunka, a Japanese concept translating to mean “production leveling.” The goal of Heijunka is to smooth out production to a constant and predictable rate, reducing Mura (unevenness) which will in turn reduce Muda (waste). Heijunka is a technique that allows you to best optimize capacity and meet demand while maintaining a stable flow of work, effectively facilitating just-in-time (JIT) production.
Production is leveled through one of two avenues:
- Leveling by volume: Leveling production by volume is essentially leveling it by the average volume of orders. Instead of running production based off of orders in real time, it establishes a stable work flow by determining average demand and leveling production to meet that demand. If a company receives a different number of orders every day for instance, the average demand for the week would be calculated and divided among the work week for level production.
- Leveling by product/type: If a company is making a family of different products, leveling by type is the way to go. The goal is to create a production sequence that can create a variety of products at one time, rather than having to produce each variation in a large batch. Instead, the facility is optimized for quick changeover times and a flexible assembly line.
Heijunka boxes are a visual control tool used within Heijunka to effectively schedule and level production. A Heijunka box consists of rows and columns, with each product listed in a row. The corresponding vertical columns represent production intervals, and within the matrix you can spread out production evenly and easily. At this point, you may choose to integrate another Lean manufacturing tool, Kanban cards. Kanban cards act as a trigger for production can be placed within the matrixes to indicate exactly what needs to be produced, when it needs to be produced, and how much must be produced.
