Buffer (Production)

A production buffer is a type of inventory allocated specifically as a hedge against variation. The root cause of the unpredictability may be due to the normal variation of a process, or any of a variety of types of special cause variation. The latter causes include things like supplier unreliability, machine breakdowns, and high defect rates.

The size of the buffer is related to the frequency and duration of the problems, and to the ease of replenishment.

In most cases, buffer is an alternative term for “The process is not really fixed, so pile up some more inventory here to make sure when things go wrong, production can stay on track.” The point of that comment? Buffers should be looked at with disdain and should be eliminated as soon as possible.

That said, when a process is not refined, there is a need for temporary and limited buffers. The most common location is immediately prior to a bottleneck. Because the bottleneck has no catch-up capacity, production will suffer if the bottleneck is starved. The buffer prevents that from happening when problems occur upstream. If a supplier to the bottleneck has a problem, the constrained resource will not run out of materials.

In most cases, even when used in an appropriate location, buffers tend to contain excessive quantities. That happens when there is little effort to streamline and improve the supplier process. Large buffers are necessary to compensate for the untreated problems.

Be careful about letting buffers into a facility. Once people recognize that there is an accepted form of excess inventory, all the materials and work-in-process that are lying around the facility become known as buffers. Maintaining a pile of 10 parts as a buffer tends to be accepted as a valid production practice, while the same 10 overproduced products has a negative connotation. Once this mutated definition of buffers takes hold, inventory has the potential to creep up or get re-categorized as a buffer. Avoid buffers as much as possible. They detract from flow. They tie up your working capital. They increase the space you need to work.