What Is Heijunka?
Heijunka (hay-JUNE-kah) is the Japanese term for production leveling — distributing production volume and product mix evenly over time. Instead of building all of Product A on Monday and all of Product B on Tuesday, heijunka spreads both products across every day (or every shift, or every hour).
Heijunka attacks mura (unevenness), which Toyota considers the root cause of both muri (overburden) and muda (waste). When demand is lumpy, everything downstream suffers: overtime one week, idle time the next; inventory spikes then shortages; suppliers whipsawed by erratic orders.
Two Types of Leveling
| Type | What It Levels | Example |
|---|---|---|
| Volume Leveling | Total quantity per period | Instead of 800 Monday / 200 Tuesday / 600 Wednesday, produce 500 every day |
| Mix Leveling | Product variety per period | Instead of AAAA-BBBB-CCCC, produce ABCABC — every product every interval |
Volume leveling is easier and should come first. Mix leveling is harder (requires short changeovers) but delivers the biggest flow and inventory benefits.
Why Batch Production Creates Chaos
❌ Batched Schedule
- Monday: 2,000 units of Product A
- Tuesday-Wednesday: 1,500 units of Product B
- Thursday: 800 units of Product C
- Friday: Catch-up / overtime for missed production
- Result: Huge WIP, long lead times, overtime every Friday, suppliers cannot keep up, finished goods pile up then run out
✅ Level Schedule
- Every day: 400 A, 300 B, 160 C
- Repeated pattern: AABABCAABABC...
- Same total weekly volume, evenly spread
- Result: Stable WIP, short lead times, no overtime spikes, suppliers get steady demand, finished goods replenished daily
The Heijunka Box
The heijunka box is a physical scheduling device — a grid of slots where rows represent products and columns represent time intervals. Production cards (kanban) are placed in slots to create the leveled sequence. The material handler pulls cards from left to right, delivering them to the line in the planned sequence.
| 7:00 | 7:30 | 8:00 | 8:30 | 9:00 | 9:30 | |
|---|---|---|---|---|---|---|
| Product A | 🟢 | 🟢 | 🟢 | |||
| Product B | 🟢 | 🟢 | 🟢 | |||
| Product C | 🟢 |
The Heijunka Box Is a Pacemaker
The heijunka box sets the rhythm for the entire value stream. Upstream processes produce to replenish what the pacemaker process consumed. Downstream processes receive a steady, predictable flow. It replaces the MRP-driven batch schedule with a visual, pull-based rhythm.
Prerequisites for Heijunka
Leveling does not work without these foundations in place:
Implementing Heijunka
Heijunka ≠ Ignoring Demand Variation
Heijunka does not mean producing the same thing every day regardless of demand. It means smoothing the demand signal over an appropriate period (week, day) and producing to that smoothed signal. Actual customer orders are still fulfilled from a small finished goods buffer. As your system matures, the buffer shrinks because lead times shrink.
🎯 Key Takeaway
Heijunka is the missing link between kanban (pull) and stable operations. Level production eliminates the peaks and valleys that cause overtime, excess inventory, and supplier chaos. Start with volume leveling (same total output daily), then build toward mix leveling as changeover times drop through SMED. The reward: shorter lead times, lower inventory, less overtime, and a calm, predictable operation.
Interactive Demo
Compare batch vs leveled production. See how heijunka reduces inventory peaks and smooths workflow.
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