Heijunka (Production Leveling)

Heijunka is a Japanese word that means leveling. It consists of a lean manufacturing tool that helps companies level production and thus satisfy demand, reducing waste as much as possible during manufacturing.

It is one of the thirteen pillars of the Toyota Production System that focuses on achieving a balanced and efficient production process. Instead of producing items in large quantities, which can lead to overproduction or bottlenecks, Heijunka promotes a more consistent and steady production flow. 

By implementing the Heijunka board system, companies can better meet customer demand, avoid unnecessary inventory build-up, and adapt more efficiently to changes in production, thanks to its flexibility and responsiveness. 

On the other hand, it also protects your resources and team from overburden when there is a sudden increase in demand because you will be producing value based on your average sell rate and can maintain a steady pace of production that aligns with customer demand.

Principles of Heijunka

Heijunka works by smoothing the production demand and separating production from direct customer demand. To achieve this, two types of leveling are used: 

I. Volume Leveling

It ensures that the same quantity of products is produced each day, regardless of variations in demand, allowing a consistent production pace and helps avoid peaks and overburden in workload. 

For instance, let’s assume you receive an average 20 t-shirt orders per week, but the number varies each day (e.g., 3 on Monday, 10 on Tuesday, 5 on Wednesday, etc.). In such cases, it would be beneficial to apply Heijunka principles to level the production volume.

Doing so allows you to create a consistent workflow and process around five orders daily, ensuring you meet the average demand by the end of the week. This approach brings stability in your operations and helps you fulfill customer orders without experiencing sudden spikes or drop in workload. 

II.  Leveling by Type

Here, different types of products are produced within the same time frame rather than producing large batches of single products. It helps level production based on the average demand for each product you are manufacturing and organizes your work around it. 

For example, a clothing manufacturer that produces t-shirts, hoodies, and pants. Instead of producing a large batch of t-shirts, followed by a batch of hoodies and then pants, the manufacturer produces a certain quantity of each product type every day.

Now, let’s suppose the manufacturer determines the average daily demand for t-shirts is 10, and for hoodies, it is 5 and 3 pairs of pants. They would produce a balanced quantity of each product daily, such as two t-shirts, one hoodie, and a pair of pants. This ensures a steady production flow and prevents excessive inventory buildup or shortages.

By combining these two types of leveling, Heijunka can respond to changes in demand without significantly changing production. This can be achieved by creating an inventory “cushion” that separates production from direct customer demand.

How to Achieve a Heijunka Flow?

Achieving Heijunka is challenging and requires an organization to stay committed to its Lean implementation processes. Balanced production schedules are usually linked to well-implemented Lean practices. A business can follow these practices to achieve Heijunka: 

• Step 1: Standardize work

  Trying to standardize work is an easy way to identify how and where to make improvements. During this process, teams will learn to distinguish between internal and external work, follow the set procedures, and manage errors effectively.

• Step 2: Work on improving the takt time

  A lean organization works based on how quickly customers want their products. This timing, known as takt time, helps align production with customer demand and reduces waste. The production team should use Kanban to manage both the work needed and the materials based on customer orders.

• Step 3: Sequencing

  Work should be organized to create many small batches instead of one large one, and orders should be delivered in the same sequence they were received. At Toyota, the ordering of materials and production follows the Just-in-time (JIT) approach, meaning products are delivered to customers exactly when they need them. Standardizing work also involves optimizing the system's ability to quickly change tools and adjust SMED, which helps make efficient sequencing possible.

Benefits of Heijunka

Heijunka plays an important role in implementing Lean manufacturing principles. It helps organizations balance product demand, respond to customer preferences, and average production volume over time. With these in play, companies can enjoy the benefits of:

Improvement in Production Efficiency: Leveling the workload prevents resource overload and reduces downtime, allowing greater utilization of resources and improving productivity. 

Waste Reduction: By balancing production and demand, you avoid overproduction and excessive inventory, two of Lean's main types of waste. 

Reduce Work in Process: Maintaining a consistent and balanced workflow reduces the amount of partially finished products waiting between different stages of production. 

Improved Efficiency: Avoiding overloads and downtime can help achieve more efficient use of human resources, machines, and equipment, reducing wasted time and unnecessary movements.

Reduction in Preparation Time: Producing smaller and more varied batches reduces the time needed to prepare and configure equipment and machines to change from one product to another. 

Less Storage Space: Maintaining lower and more constant inventory levels requires less space for storing raw materials, work in process, and finished goods.

Heijunka vs. Batching

Like many concepts in Lean manufacturing, Heijunka comes from the Toyota Production System. In traditional Ford-style production, products were made in large batches. Toyota eventually recognized that this method was not effective for meeting customer needs. They found that producing in batches caused waste and put too much pressure on workers and machines, which resulted in lower profits and unhappy employees.

Heijunka, on the other hand, distributes the expected number of orders over several days. This approach called “leveling by volume,” means making the same number of products each day, which helps avoid sudden increases in demand that can overwhelm the production area. Unlike batch production, a Heijunka system lets manufacturers operate with less inventory and shorter lead times. It also provides a more predictable and stable production process, making it easier to adjust to changes in demand without creating excess inventory or waste.

Heijunka Box (Heijunka Kanban)

A Heijunka box is a visualization tool used in Heijunka for scheduling and maintaining a consistent workflow in production. It can be a physical wall schedule or a software program divided into a grid of boxes. Each column represents a specific period, such as shifts, days, or weeks, and lines are drawn to visually separate the schedule into different time segments.

The box contains colored cards called Kanban cards in various box slots that help workers see which jobs are lined up and in what quantity products will be manufactured in a specific period. Using a Heijunka box helps manufacturers evenly distribute the production of various products and also helps workers know what they need to work on for the current period. 

By doing this, companies can avoid excessive inventory and reduce the risk of overproduction.

Methods for Implementing Heijunka

Implementing Heijunka involves a structured approach to achieve a smooth and balanced production flow. Heijunka in Lean Manufacturing addresses fluctuations in demand and minimizes waste. By implementing Heijunka, organizations can optimize their production processes and improve customer satisfaction.

Implementing heijunka begins with understanding your work pace and considering the following key concepts.

In Summary

Heijunka is a Lean method that helps optimize production processes. By implementing Heijunka, you can effectively organize your workflow to meet customer demand promptly and avoid overproduction, reducing inventory costs. 

Additionally, Heijunka protects your team from being overwhelmed by sudden spikes in demand, ensuring a more balanced workload. It allows you to meet your defined takt time, the rate at which products need to be produced to meet customer demand. Ultimately, Heijunka ensures that your pull system operates efficiently, helping you streamline operations and improve overall productivity.