Heijunka

Heijunka is the Japanese term for level-loading or production leveling. It is intended to smooth out the peaks and valleys of customer demand into something flatter to create conditions that make standardization easier. It also stabilizes the product mix to support Standard Work.

Heijunka, pronounced High-June-Kuh, is a workaround for variations in demand. It essentially consolidates short-term demand into larger buckets, and then parcels it out in daily buckets.

The premise behind heijunka is that bigger demand windows vary less than smaller ones. January and February’s average demand (big demand window) probably look a lot alike. A small demand window from 1:00-2:00 on March 16^th might look quite different than 2:00-3:00 on the same day.

This lets Lean manufacturers build in repetitive sequences instead of running a single model for a long period. Heijunka turns AAAAAABBBBBBCCC into ABABC, ABABC, ABABC.

Because of the shorter runs of each product, inventory needed on hand drops. It also allows for some production flexibility. (I discuss this concept in more detail in my Lean tutorial, Structuring Standard Work.)

For heijunka to be effective, demand must be monitored. When demand shifts, the model mix has to be adjusted as well. Heijunka is also limited to moderate demand fluctuations. Dramatic demand shifts need more extreme measures.

Why Does Heijunka Work?

Customer orders, in the short term, tend to be highly variable, but as the window of time increases, there is more evenness to demand. For example, weekly demand over a 3-week period might be 200, 218, 197-fairly close. The Monday demand for those same three weeks could be 37, 61, 47-not quite as stable. And day-to-day demand might fluctuate even more wildly-Wednesdays might be the day that three of your biggest customers all place their orders (hey, not everyone is Lean, right?).

Your product mix also likely has similar variation. The breakdown of what people order every day probably fluctuates. Over a longer period, product mix is probably smooth, but the day to day change in product mix might be significant.

Heijunka Has Limitations

Heijunka is a workaround for uneven demand. It is the bridge between how customers order and how a Lean company operates.

Think about this: Lean promotes pull, and at the same time pushes for standard work. In truth, the two concepts don’t play very well together. Standard work promotes rhythm. Pull promotes responsiveness. If your customers don’t buy at an even pace…well, you can see the problem.

In Lean, Heijunka aims to find a way to level the demand on the factory to prevent having wild shifts in production. In effect, a heijunka system uses actual demand from customers over a long period to set production rates, and then stabilizes the short-term demand based on those average rates. That way, you only have to shift production schedules to match long term changes in customer demand. You don’t chase the small, day-to-day fluctuation.

An Example of Heijunka

In the example above, the average demand is 205 units. If you set your production at 41 per day, you would be balanced with your demand, on average. You would end up with 4 extra units the first Monday (overproduction), and then run 20 units behind the second Monday. But, at 41 per day, you’d end up flush on the third Friday-even though you might have only gotten the daily demand to match production a couple of times.

For the three-week period, you were right on the money. Plus, you kept from having to wildly shift production around in your facility. Just remember–during those three weeks, you were either pulling from a finished goods inventory, or increasing your order backlog whenever your demand wasn’t identical to your production.

Heijunka is a Tradeoff

Heijunka is simply trading the higher costs of wild demand swings for the lower costs of warehousing a small controlled quantity of finished goods. But as with any workaround, it is not actually the best solution.

It is far better to create a responsive production system that can adjust efficiently within a specific demand window. This can be accomplished with a flexible workforce, but it takes great skill in continuous improvement to pull it off. You’ll also need excess infrastructure, as you’ll have some areas sitting idle when people are moved around. The key is to be creative in how you battle demand variation without resorting to massive piles of inventory and long production runs.

Benefits of Heijunka

• Heijunka provides consistency in processes.
• Heijunka presents stable demand to suppliers.
• Heijunka makes processes predictable.

Drawbacks of Heijunka

• Heijunka trades inventory or lead time for stability
• Heijunka limits rapid adjustments
• Heijunka requires industrial discipline
• Heijunka can only handle moderate variations in demand