1. Method Name

Heijunka (平準化)

2. Alternative Names

Production Leveling, Production Smoothing

3. Brief Description

Heijunka is a method for leveling the production load in terms of both volume (quantity) and product mix (type). Instead of producing large batches of a single product based on current orders, smaller batches of various products are produced in a repeating cycle.

4. Purpose / When to Use

It is used to eliminate extreme fluctuations in demand that cause overload (Muri) and unevenness (Mura) in processes. It creates a predictable and stable environment for employees and suppliers. It is an advanced Lean technique that is only possible after the successful implementation of SMED (rapid changeovers).

5. Procedure / How to Apply It

1. Analyze demand: Determine the total demand over a specific period (e.g., a month) for each product type.
Example: Monthly demand is 1,000 units of Product A, 500 units of Product B, and 500 units of Product C.
2. Calculate the production cycle: Determine the smallest possible repeating production pattern. In our example, the ratio of A:B:C is 2:1:1. The basic cycle could be A-B-A-C.
3. Divide production into small, even batches: Instead of producing only Product A one week and Products B and C the next, distribute production evenly across each day
.* Traditional approach (without Heijunka):
A-A-A-A-A-A-A-A-B-B-B-B-C-C-C-C* Heijunka approach: A-B-A-C-A-B-A-C-A-B-A-C...
4. Implement the Heijunka Box: The visual tool known as the “Heijunka Box” (or Kanban board) is often used. It is a grid-based board where the rows represent products and the columns represent time intervals (e.g., hours). Kanban cards are placed in the individual cells to indicate what is to be produced and when. At regular intervals, the operator takes the next card from the box and produces according to it.
5. Ensure the Prerequisites: Heijunka requires very short setup times (SMED) and high process stability (low failure rate and high quality).

6. A Real-World Example

The car manufacturer Toyota receives orders for various models with different configurations (e.g., sedan, station wagon, with or without a sunroof). Instead of producing 500 sedans and then retooling the line to produce 300 station wagons, they use Heijun-kyu. Their assembly line is capable of producing cars in small batches or even in a one-piece flow sequence (e.g., sedan-station wagon-sedan-sedan-station wagon). This allows them to respond flexibly to demand while maintaining a stable workload for suppliers, who must deliver parts in small, regular batches.

7. Benefits

- Predictability and stability: Reduces stress and chaos in the workshop and throughout the supply chain
.- Reduced inventory: Eliminates the need to hold large inventories of finished products “just in case.”
- Flexibility: The company can deliver the product the customer wants much faster
.- Optimal use of resources: Prevents alternating periods of overload and idleness for both workers and machines.

8. Risks / Limits

- Requires extremely short changeover times: Without successful SMED, Heijunka is impossible, as frequent changeovers would destroy productivity.
- Requires high discipline and stability: Processes must be highly reliable (high quality, low machine failure rates).
- Complexity of implementation: It is one of the most challenging Lean techniques to implement and maintain properly.
- Not suitable for custom manufacturing with unique products: Heijunka works best with product families that have a certain degree of repeatability.

9. Practical Tips

- The Heijunka Box is a key visual tool: It helps everyone on the shop floor understand what will happen in the coming hours and how production orders flow from one to the next.
- Start by leveling volume, then add product mix: First, aim to produce the same total quantity of products every day. Only then should you address balancing the mix of different product types
.- Don’t forget your suppliers: Communicate with suppliers and involve them in the system. For them, Heijunka means stable and predictable orders instead of sporadic large orders.