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How can production leveling help companies become lean?

Eliminating waste is an important principle in lean production. Here's a look at how heijunka, or production leveling, can help achieve that.

For companies that want to follow lean principles, production leveling is an important concept to know.

The driving principle behind lean manufacturing is to eliminate production waste whenever and wherever possible. One way to do that is to eliminate variation, which is also the prime objective of Six Sigma, often associated with lean.

Variation in production is inherent in the start-stop nature of traditional batch manufacturing. Production cells and lines, when properly designed and operated, eliminate that start-stop variation by enabling a steady flow of work that creates a steady demand for supplying lines, departments and suppliers -- helping them eliminate variation in their own processes -- and provides a steady flow of products to downstream processes and customers.

The benefits of level production -- or continuous, repetitive or flow production, as it may be called -- can only be achieved if the cell or line is operated at the steady pace for which it was designed, with the least amount of variation possible. The process of production leveling, also known by its Japanese term heijunka, is based on maintaining that smooth flow of work, meaning that work is released to the plant at the required even rate, and that every effort is made to eliminate interruptions to that even flow.

The Toyota Production System uses the Japanese term heijunka to mean production leveling and links heijunka to the reduction of muda (waste), as well as mura, another form of waste referring directly to unevenness or variation.

Lean manufacturing is well-known for its focus on physical methods of control, such as Kanban cards for triggering inventory replenishment. A heijunka board is a physical, visual scheduling tool that often takes the form of a magnetic board or whiteboard divided into a grid, with the columns representing periods of time and the rows listing or displaying the work to be done.

Another common form of visual representation is the heijunka box, an array of pigeon holes arranged in columns that represent time intervals and rows representing products. Job cards or Kanbans are placed in the pigeon holes to indicate the work that is scheduled for that shift or day. Workers remove the card when starting the work and send the card to the next operation or department to be placed in the proper slot in that department's heijunka box when they're done. 

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