What is Production leveling / smoothening and how to improve with digital tools?

Production leveling or smoothing allows production to closely follow customer demand. Within the Toyota production system the Japanese term Heijunka, which means leveling, describes several techniques to achieve this target. Through leveling of volume and model-mix manufacturing systems are able to operate at a constant rate, which is more efficient than rapid ups and downs.

Why should production be smoothened?

In daily operations, manufacturers encounter several challenges, that influence shopfloor activity and hinder smooth operations such as:

  • Rush orders
  • Bullwhip effect
  • Cancellations
  • Demand fluctuations
  • Shortages
  • Defects

Some of these challenges have the potential to disrupt the smooth flow of goods and cause management to act in a fire fighting mode. Once the system is trapped in such a mode, it is difficult to bring operations back to normal. Instead, operators are often more focused on handling urgent issues, than improving the organization. Figure 1 displays the dilemma in which manufacturers are trapped, having to respond to fluctuating orders from customers while forwarding these fluctuations to their suppliers. 

Leveling is trying to make production more efficient and robust against frequent changes while saving costs. To do this manufacturers need to understand that the cause is most often found within batching products. Since each product requires the specific setup of the machine it is produced on, multiple products of the same kind are bundled together and produced in batches. Figure 2 displays the impact of producing in high batches. Although the daily demanded volume of a single product is varying between 10 and 30 pieces, batches of 80 pieces are produced once a safety stock is reached. Since the demand strongly fluctuates between products, multi-product manufacturing in batches becomes more challenging.

If several products are produced using voluminous batches, warehouse capacity and storage costs increase while flexibility is strongly limited, due to long forecast cycles. If products are manufactured in several stages, fluctuations are increased even further through the introduction of interim storage for parts. Instead of job shop production, flow shops with balanced lines, cycle times, optimized setups with SMED, and a production sequence (EPEI) are introduced to enable the reduction of fluctuations (see figure 3). 

By bringing down batch sizes to the actual customer demand, warehouses don´t need to store as many products and parts anymore. At the same time, demand forecasting is not needed to the extent it has been before and order times are significantly reduced. Therefore operators can focus on working at a steady pace while managers do not have to hunt and accelerate orders with tight due dates.

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How is production leveling implemented?

Production leveling involves leveling product mix and volume. Leveling volume, hence reducing batch sizes, can only be accomplished with lower setup times. The lean method to lower setup times is called SMED - Single Minute Exchange of Die. Its target is to reduce setup times from several hours into single minute durations. Once setups are reduced smaller batches can be produced. To improve production leveling with digital tools, WORKERBASE provides an App Suite for reducing setup times. With the WORKERBASE AppBuilder, individual setup instructions can be combined to form step-by-step instructions for machine setup. The WORKERBASE rule engine allows to create flexibel rules which in turn allow to split long setup routines into individual tasks that are automatically assigned to different persons. By using the machine setup app, SMED can be implemented and supported with digital tools.

Most products are manufactured in several stages. Unbalanced processing times within these stages lead to an increase of WIP - Work in progress inventory and bottlenecks in production. To prevent bottleneck and WIP generation processing times between stations are aligned to follow customer demand. The introduction of cycle time within the lean line balancing method aims at generating a standardized time for all stages of production. Finally EPEI - Every Part Every Interval - is leveling the model mix by splitting daily volumes into smaller cycles. 

Together these 3 methods form the Heijunka concept and allow manufacturers to smoothen their production activities and react fast to customer demands. These methods can be increased even further through the use of digital tools, e.g. by using the App Suite for reducing setup times or the Material Management App Suite. The benefits of lean production and digital possibilities combined, allow fast communication between humans, machines, and legacy systems. Providing the right information within the right moment to the best-fitting employee is boosting production efficiency by at least 25%. 

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