Heijunka — Level Scheduling

A short brief before you play

Heijunka (pronounced hay-June-kah) is Japanese for levelling. It means smoothing production so the same amount, and the same variety, is made at a steady pace, instead of lurching to match every rise and fall in customer orders.

The three enemies it fights

Mura unevenness. Orders arrive lumpy, so if you chase them the workload swings wildly.
Muri overburden. On the peak days people and machines are pushed past their limit, so quality and safety suffer.
Muda waste. On the quiet days people and machines sit idle. Mura causes both muri and muda, so levelling attacks the root.

Chase versus level

Chase means produce exactly what was ordered each day. It sounds efficient, but it forces overtime and overburden on busy days and idleness on slow days, and it needs a flexible workforce you rarely have.

Level means produce close to the average every day, and hold a small buffer of finished goods to absorb the swings. The workload becomes calm and predictable, staffing is stable, and quality steadies. The price is a modest amount of inventory, which is usually far cheaper than the chaos of chasing.

Two kinds of levelling

Volume levelling: make the same quantity each day (the average), not the daily order.
Mix levelling: make a little of every product each day in a repeating pattern, rather than one product in a long campaign. This is what the Heijunka box shows: instead of AAAAA then BBB then CC, you run a level sequence like A B C A B A C. Any customer can then be served on any day.

Mix levelling means more changeovers, so it depends on quick changeover. That is why Heijunka and SMED (single-minute exchange of die) are taught together: SMED makes the frequent changeovers cheap.

A worked example: Sunrise Foods, Karachi

Sunrise makes three sauce lines, A, B and C. Last week distributors ordered 8, 30, 5, 40 and 17 cases from Monday to Friday, a total of 100 for the week, so the average is 20 a day. The line can make at most 25 in a day.

Chasing the orders means 8 on Monday (people idle), then 30 and 40 on Tuesday and Thursday. Both are above the ceiling of 25, so the line is overburdened on two days, ships late, and pays overtime, while Monday and Wednesday are slow. That is mura creating muri and muda at the same time.

Levelling to 20 a day removes every overburden day and steadies the crew. Sunrise starts the week with a small finished-goods buffer, builds a little stock on the light days and draws it down on the heavy days, and still serves every order. For the mix, instead of a Monday A-campaign it runs a daily pattern such as A B C A B A C A B A, so a distributor wanting sauce C on Wednesday no longer waits for the next C campaign.

The lesson executives take away: the demand did not change, but by levelling the response to it, Sunrise cut overtime, protected quality and improved delivery, at the cost of a small, deliberate buffer.

How to use the tool

Open the Level the Load (tool) tab.
Edit the daily demand and the daily capacity to match a situation you know.
Toggle between Chase demand and Level it (Heijunka) and watch the peak load, the overburden days and the inventory change.
Set a weekly mix (A, B, C) and read the level sequence the Heijunka box produces.
When you are done, click Submit to facilitator to record your result.

This week's customer demand

Edit the daily demand and the daily capacity, then compare the two ways to schedule.

Daily capacity (max the line can make in a day):

Production schedule

Chase versus Level, side by side

Measure	Chase demand	Level (Heijunka)

The Heijunka box (mix levelling)

Levelling is not only about volume. Instead of making one product in a big campaign, produce a little of every product each day in a repeating pattern. Set a weekly mix:

A B C units per day

Each day now ships the full mix, so any customer can be served any day. The cost is more frequent changeovers, which is exactly what SMED exists to make cheap.

Heijunka: Level the Load