Production leveling is the art of distributing work on the shop floor to prevent bottlenecks during peak periods. Atsushi Niimi, president and CEO of Toyota Motor Manufacturing North American, Inc., recently explained the concept of heijunka – or production leveling – in a speech at Manufacturing Week in Chicago.

     The simple definition of heijunka is production leveling.

     Think about the last time you went to a baseball game. In the hour before the first pitch, people trickled in, took their seats and got ready for the game. But when that last pitch is thrown, everyone stands and heads for the exits. What happens? A massive bottleneck.

     This shows the needs for heijunka.

     Like many aspects of the Toyota Production System, heijunka was born out of necessity.

     In the early 1950’s, Toyota needed to increase production of trucks for the United States to use in the Korean War. Unfortunately, there was a shortage of everything from raw materials to parts.

     We could not get things in the quantity or time needed. In fact, we literally could not do any production during the first half of the month. Those two weeks were spent gathering the parts that were arriving in no particular order. Then we spent the second half of the month assembling the trucks.

     We realized this system would never work if production levels increased. So, out of this challenge, the system of heijunka was developed. Heijunka is one of the main foundations of the Toyota Production System, along with standardized work and kaizen, or continuous improvement.

     If we matched (production) exactly to customer orders, some days production would be very high and some days it would be very low. But you would always need to have the machinery, manpower and materials to produce at peak production. Of course, there would be significant idle time during the valleys. We call this waste muda.

     The solution is to take all the orders for a certain period - a month... a week... a day — put them in a pool and then level out the production. This is heijunka.

     Let’s say that over the period of a week, we get 700 orders for Camrys and 300 orders for Avalons. Now, of course, those orders don’t come in at 100 per day of Camry. Some days it may be 175, other days 65. But we pool together all the Camry and Avalon orders and...

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