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Heijunka is one of the elements of JIT (Just In Time) Manufacturing of Toyota Production System.
Definition
The process of smoothing the type and quantity of production over a fixed period of time
Benefits
- Enables production to efficiently meet customer demands (more flexibility)
- Avoids batching
- Reduces finished goods inventories
- Reduces capital costs
- Stable work force
- Reduces production lead time
Heijunka Example
- Level Production by Quantity of Items
Routinely received orders for 500 units/wk:
- 200 units on Monday
- 100 units on Tuesday
- 50 units on Wednesday
- 100 units on Thursday
- 50 units on Friday
Level production at 100 units/day Keep small stock of finished goods
- Leveling Production by Type of Goods
- Product A – 5 units/wk
- Product B – 3 units/wk
- Product C – 2 units/wk
- Product D – 2 units/wk
Mass Production: AAAAABBBCCDD Lean Level Production: AABCDAABCDAB
Conversion Steps
1. Determine the total monthly demand for each type of product Example:
- Product A = 1000 units
- Product B = 200 units
2. Establish the weekly product requirement Example:
- Product A = 1000/4 = 250 units
- Product B = 200/4 = 50 units
3. Determine the number of days during the production month: Example:
- 4 weeks x 5 days = 20 days
4. Calculate the daily requirement for each product type
Example:
- Product A = 1000/20 = 50 units
- Product B = 200/20 = 10 units
- Total daily production = 60 units
5. Compute the build ratio and the production frequency for each product type Example:
- Product A = 50/10 = 5
- Product B = 10/10 = 1
- Production frequency = 60/10 = 6
6. Determine the build frequency Example:
- Product A – 5 units will be produced every 6 units
- Product B – 1 unit will be produced every 6 units
7. Set a build schedule Example:
Heijunka Box
A tool used to level the mix and volume of production by distributing kanban within a facility at fixed intervals
- Each horizontal row is for one part number
- Each vertical column represents identical time intervals for paced withdrawal of kanban
- The slots represent the material and information flow timing
- The kanban in each slot represents one pitch of production for one part number
Pitch = the takt time multiplied by the pack-out quantity
- A: 20 min
- B: 10 min
- C: 40 min
Product D: Product E = 2:1 – they share a production process with a pitch of 20 min.
- Heijunka consistently levels demand by short time
increments (instead of releasing a shift, a day or a week’s
worth of demand to the floor)
- It levels demand by mix ensuring that products d and e are produced in a steady ratio with small batch sizes.
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