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Heijunka (Level Production) between Theory and Application
Heijunka is one of the elements of JIT (Just In Time) Manufacturing of Toyota Production System.
The process of smoothing the type and quantity of production over a fixed period of time
- 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
- 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
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: - BAAAAABAAAAABAAAAA
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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