SC QUALITY GUILDHeijunka production leveling
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Enter each product's demand for the period. Get the daily quantities, the shortest repeating mix pattern, takt or pitch, the day-by-day plan, and a check that the pattern meets demand.
ON THE EXAM · CSSBB VII.B.2 · FREE · NOTHING YOU TYPE LEAVES YOUR BROWSER
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What heijunka levels
Heijunka is production leveling. It smooths two things:
- Volume: the same total every day, rather than a light Monday and a heavy Friday.
- Mix: a little of every product every day, in a short repeating pattern, rather than all of A on Monday and all of B on Tuesday.
Batching by product looks efficient because it cuts changeovers. But it makes the upstream processes and suppliers see huge swings: a week of demand for A's parts, then none. It also means a customer who wants B on Monday waits, or is served from stock. A leveled schedule lets every upstream kanban loop run at a steady rate, with less stock.
How the pattern is built
- Daily quantity: each product's period demand divided by the working days.
- Pattern: the daily quantities divided by their greatest common divisor. With 240 A, 120 B, 60 C and 60 D a day, the divisor is 60, so one pattern holds 4 A, 2 B, 1 C and 1 D: eight units, run 60 times a day.
- Sequence: the units in the pattern are spread as evenly as possible. At each position the tool places the product that is furthest behind its even share, which for this mix gives ABACDABA. This is a simple form of the goal-chasing method.
- Takt: available time divided by the total daily quantity. When leveling by containers, the same calculation gives the pitch: the time to make one container, which sets how often material is moved and how the slots of a heijunka box are spaced.
When the daily quantities share no common divisor, the exact pattern is the whole day. Setting fewer repeats per day gives a shorter pattern with a small mismatch; the checks show it product by product, and the day-by-day table still meets the period demand exactly.
What it needs
Leveling the mix means more changeovers, so it depends on short setups (SMED). It also needs some finished-goods stock to absorb the gap between the leveled schedule and daily orders. Products needed less than once a day are better run on fixed days than squeezed into the daily pattern.
The heijunka box
On the floor the pattern is often run with a heijunka box: a rack with a column for each pitch interval and a row for each product. Kanban cards are loaded in the pattern, and a material handler takes one column at each pitch, so the line is told what to make next in small, level steps.
On the exam
The CSSBB lists heijunka (production leveling) among the tools for cycle-time reduction, with continuous flow and SMED (VII.B.2). Expect to explain why leveling the mix helps the upstream processes, to work out a daily quantity and a repeating pattern from a product mix, and to relate takt and pitch.