The one critical requirement for a TPS approach to be effective is that the production plan should be leveled both in quantity and in mix. This is indicated by the Japanese term Heijunka (平準化), which stands for “leveling” or “smoothing”. When implemented correctly, Heijunka elegantly –and without haste – helps organizations meet demand while reducing wastes in production and interpersonal processes. Once the production level is more or less the same or constant for a month, you will be able to apply pull systems and balance the assembly line. But if production levels—the output—varies from day to day, there is no sense in trying to apply those other systems, because you simply cannot establish standardized work under such circumstances.
Heijunka does not build products according to the actual flow of customer orders, which can swing up and down wildly, but takes the total volume of orders in a period and levels them out so the same amount and mix are being made each day. The approach of TPS from the beginning was to keep batch sizes small and build what the customer (external or internal) wants. In a true one-piece flow, you can build Products A and B in the actual production sequence of customer orders (e.g., A, A, B, A, B, B, B, A, B…).
The problem with building to an actual production sequence is that it causes you to build parts irregularly. So if orders on Monday are twice those on Tuesday, you must pay your employees overtime on Monday and then send them home early on Tuesday. To smooth this out, you take the actual customer demand, determine the pattern of volume and mix, and build a level schedule every day. For example, you know you are making five A’s for every five B’s. Now you can create a level production sequence of ABABAB. This is called leveled, mixed-model production, because you are mixing up production but also leveling the customer demand to a predictable sequence, which spreads out the different product types and levels volume.
There are four benefits of leveling the schedule:
- Flexibility to make what the customer wants when they want it. This reduces the plant’s inventory and its associated problems.
- Reduced risk of unsold goods. If the plant makes only what the customer orders, it doesn’t have to worry about eating the costs of owning and storing inventory.
- Balanced use of labor and machines as the plant can create standardized work.
- Smoothed demand on upstream processes and the plant’s suppliers. If the plant uses a just-in-time system for upstream processes and the suppliers deliver multiple times in a day, the suppliers will get a stable and level set of orders. This will allow them to reduce inventory and then pass some savings on to the customer so that everyone gets the benefits of leveling.
Asprova users are blessed with the competency of leveling the schedule, including giving them the ability to plan every detail of production meticulously and standardizing work practices. The reliable information accessible from our advanced planning and production scheduling function enables production to efficiently meet customer demands while avoiding batching and results in minimum inventories, capital costs, manpower, and production lead time through the whole value stream.