Level production, known by its Japanese name Heijunka, is a structured approach within lean manufacturing designed to stabilize the production schedule and flow of work. This method seeks to move away from erratic, stop-start production cycles that are common when reacting immediately to every customer order fluctuation. By carefully distributing demand over time, Heijunka establishes a predictable rhythm for the entire manufacturing process, which is foundational for achieving operational stability and efficiency.
Defining Level Production (Heijunka)
Heijunka translates roughly to “leveling” or “smoothing” and represents a core principle developed within the Toyota Production System (TPS). The central purpose of this practice is to minimize mura, the Japanese term for unevenness or fluctuation in an operation. Allowing natural variability from customer orders to dictate the production schedule introduces instability throughout the entire value chain.
The goal of level production is to match the average rate of customer demand over a defined period, rather than attempting to meet immediate demand spikes. For example, if a company receives 500 orders a week, Heijunka aims to build 100 units every day, regardless of daily order fluctuations. This deliberate smoothing provides a predictable pace that benefits internal operations and external suppliers, creating a more sustainable workflow.
The Mechanics of Leveling Production Volume
Leveling production volume addresses the quantity of products built over a specific time frame, ensuring the total workload remains consistent day-to-day. A system that reacts to large, sporadic orders often results in overcapacity or underutilization, forcing manufacturers to hire temporary staff or pay excessive overtime when demand spikes.
Implementing volume leveling means calculating the average daily or weekly demand and committing to producing that exact amount consistently. For instance, if average demand is 1,000 units per week, the leveled schedule dictates producing 200 units every day. This stable output minimizes the need for drastic adjustments to labor or equipment usage, providing a predictable load on internal resources and allowing for better maintenance planning and a more stable workforce.
The Mechanics of Leveling Product Mix
Leveling the product mix addresses the variety of items built by sequencing different products in small, repetitive cycles. Traditional production focuses on large, segregated runs (e.g., all of Product A, then all of Product B), which creates long lead times and excessive finished goods inventory.
Heijunka instead uses a sequence of small batches, often called “pitch,” based on the takt time needed to meet customer demand. A leveled mix might sequence products as A-B-C-A-B-C throughout the day. This approach requires the ability to switch quickly between product types, enabling flexibility and responsiveness. By producing a little bit of everything frequently, the manufacturer can respond to customer orders with minimal delay.
Tools and Techniques for Implementing Heijunka
The practical management and visualization of a leveled schedule often relies on a physical tool called the Heijunka Box, or Leveling Box. This board is typically divided into a grid where vertical columns represent product types and horizontal rows represent short time intervals (e.g., 10-minute slots). Production orders are represented by kanban cards or visual tokens placed into the slots of the box.
The Heijunka Box allows operators to see the leveled sequence clearly and pull the next card as they complete the current task. This visual management system ensures the production floor follows the schedule rather than defaulting to the largest or most urgent order. Successful mix leveling relies on Single-Minute Exchange of Die (SMED), which ensures the time required to change over equipment between different product types is extremely short. Without rapid changeovers, frequent small-batch production becomes impractical due to lost production time.
Key Benefits of Level Production
Implementing level production creates stability that cascades positive effects throughout the organization and supply chain. It reduces the need for large buffers of inventory, both raw materials and finished goods, because production aligns closely with the average demand rate and builds a mix of products frequently.
The stable schedule reduces stress on equipment, which contributes to better longevity and reliable performance. This consistency also stabilizes demand placed on suppliers, enabling them to level their own production and delivery schedules. The rhythmic, standardized work facilitated by Heijunka improves overall product quality by allowing personnel to focus on a consistent process without the fatigue and errors caused by rushed, erratic work cycles.
Level Production vs. Traditional Batch Production
Traditional batch production operates on a “batch and queue” model, manufacturing large quantities of a single item before a major setup change. This approach creates significant work-in-progress inventory that sits idle, increasing the overall lead time required to fulfill a customer order. Large batches also amplify fluctuation, as a delay or defect in one step halts the production of thousands of units.
Level production, in contrast, exposes inefficiencies by forcing the frequent repetition of small batches and quick changeovers. This methodology prevents the accumulation of large inventories that traditionally hide underlying problems like unreliable equipment or lengthy setup procedures. By minimizing the “queue,” the leveled approach makes any disruption immediately visible, compelling continuous improvement efforts. This focus on stability provides the foundation for implementing other lean principles upon a reliable and predictable operating environment.