In any study of operations management or lean manufacturing you are likely to hear the terms “push” and “pull” used frequently in describing the overall approach to production and inventory management. “Push” refers to the traditional approach that starts with a forecast and uses MRP to create a plan, then the plant produces according to the plan. “Pull” is the Lean approach to production and inventory management based on replenishment. Nothing is produced or replenished until it is used or sold.
These two approaches are obviously quite different but neither is necessarily right or wrong, better or worse. The key is to use the right technique for the situation. A combination approach that uses elements of both can be a powerful strategy.
In a typical “batch” (also called intermittent or discontinuous) production environment where work orders track the production of fixed quantities (lots) of production, push is the toolset that establishes priorities that direct the sequence of work at work centers and manage the flow of work through the plant. These tools are all focused on the master schedule dates that are (hopefully) tied to an accurate forecast of what customers will be ordering. This is a necessary process where lead time to produce the product is longer than the lead time that the customer will accept. In other words, if the customer won’t wait long enough for us to make it, then we have to at least start production based on a forecast.
In a situation where lead times are short enough to provide the item when requested by the customer, or where the company is willing to stock enough finished goods to buffer the difference in requested vs. real lead time, then pull can be used to trigger replenishment after finished items are sold and shipped. Physical pull signals (kanban) works best where demand is stable and predictable. To take full advantage of pull, the plant should be focused on short lead time, usually through the implementation of continuous flow lines and cells.
There is ample opportunity to incorporate pull signals within a traditional push (forecast driven, batch production) environment. Companies can use kanbans and other pull techniques to move materials and trigger production, reducing paperwork and reporting. Many ERP systems today support the use of kanbans and electronic kanbans as replenishment signals.
So, there’s no need to argue the relative merits of pull versus push. Each has its place and the two philosophies can be used together to get the best inventory and throughput performance in the plant.
