Lean Manufacturing in Simple Terms: Pulling Versus Pushing

In our American culture, we are very accustomed to going to a grocery store, or a hardware store, or any other kind of store, and finding all of the items we had set out to purchase. Not only do we expect to find our desired product in adequate quantities, we also expect to find it in a variety of colors, shapes, and sizes. Let's face it. We are quite spoiled when it comes to shopping. It seems like our manufacturers and our merchants have always gone out of their way to provide large inventories of goods.

Perhaps that thought process, however, makes it difficult to grasp the idea that in a lean manufacturing world, the excessive inventories that come from improved manufacturing methods and healthy supplies of raw materials should actually be considered a form of waste.

Lean manufacturing is best achieved when the product is pulled through the system rather than pushed through the system. Let's discuss each of the two methods.

Push System. A "push" system is one where the manufacturer builds as many items as possible each day, anticipating the need in the marketplace. The product is "pushed" down to the next level of manufacturing or sales, regardless of whether it is needed there or not. The risk, therefore, is the chance that the demand will not match the manufacturer's predictions, and an excessive inventory will have to be stored, managed, and possibly even liquidated at some point in the future. Or on the other hand, if the inventory is not sufficient for the demand, the manufacturer's risk includes the potential for reduced customer satisfaction because the market wasn't properly supplied. Either way, the push system requires good information to be reasonably effective.

This may not be totally impossible. Many companies have great research groups to help determine where and when a product need will arise. Large merchant groups like Wal-Mart keep a close watch on key indicators, like the weather, during their data collection. When a hurricane appears to be bearing down on the Gulf Coast, company officials are busy dispatching post-storm necessities (such as axes, chainsaws, bottled water, and pastry tarts) directly to the stores in that vicinity. Most companies, however, are not always blessed with the kind of data collection and accuracy that would allow for good planning and inventory management. When they are wrong about an item, they often end up with product that has to be stored, and perhaps discarded. In other words, profits will eventually have to be spent for unnecessary costs such as warehousing, additional relocations, and possibly even price mark-down efforts.

Pull System. In the "pull" system, on the other hand, manufacturing is only completed when there is a downstream need, as indicated by customer requests. In our lean manufacturing world, this "customer" could be the operators in the next phase of the fabrication process, or it could be store owners wanting to purchase finished items from the manufacturer. The advantage here is that there is no excessive effort. Why build 100 widgets for August, only to find out that only 67 were needed in the marketplace? In a true "pull" system, the manufacturer doesn't have to guess how many will be needed. He only needs to react to the demand at the time. The result is a reduction in non-value-added costs, such as inventory management, warehousing, etc. The risks for the pull system include the possibility that, when the item is requested, the manufacturer will not have the raw materials or the plant capacity to produce the requested quantity in a short time. Again, customer satisfaction can be at risk. And so the key here is to make sure that the process of fabrication is already "leaned out," where all steps have significance, and where the process can be done in an efficient manner.

While the reduction of overproduction is one of the key advantages of pulling a product through a lean manufacturing process, there are other internal advantages that can be realized. For example, in many cases, where items are manufactured in large batches, each batch or lot is completely subjected to the current process before moving the batch or lot to the next production step. This could mean that an item that was processed early in the step has to wait for all of the other items in the batch to complete that process before moving on to the next step. In a pull system, those batches are broken up in to single pieces and/or smaller groups, and are moved to the next step immediately. In a lean manufacturing world, where waiting is equivalent to wasted time and dollars, keeping the product line moving is critical to efficiency.

Manufacturers contemplating a switch to the "pull" system from the "push" system should understand the need for maximized efficiency, being able to build the product quickly and getting it right the first time. They will need to respond quickly when the market demands are made known. They should also keep a close watch over the suppliers that provide raw materials, making sure there is ample flexibility to change sources if there is an interruption in the regular supply process.