The challenge of manufacturing

For as long as humans have been manufacturing things, efforts have been made to manufacture things that are the same. This seemingly simple task is anything but when put into practice. The task of manufacturing is to produce multiples of the same part, assembly, or product that are, for all intents and purposes, identical. But measurements of multiples quickly reveal that no two things produced by the same process will ever be the same (the process principle). Differences in outputs are an intrinsic and defining feature of all processes. Thus, the challenge of manufacturing is the challenge of understanding and mitigating differences. The extent to which the sequential outputs of a process or system differ is called variation.

It is easy to manufacture one of something because one of something is self-contained. Outside of engineering drawings, there are no analogues for comparing individually produced parts, assemblies or products. While measurements reveal deviations from drawings, they make no statements and answer no questions about the underlying process that produced them. They reveal nothing about how a process has behaved in the past or how it will behave in the future. In order to do that, the same process must be used to manufacture multiples. Then, and only then, can measurements of those multiples be compared and a picture of the underlying causal system be painted.

Having produced multiples of the same item, it is guaranteed that measurements of these multiples will reveal differences but it is hoped that these differences will be negligible. In the same way that no two snowflakes will ever be identical, the sequential outputs of processes will always be different. Regardless of how different multiples of an item are, the challenge of making multiples that are the same remains. Variation, whether it is recognized or not, continues to assert its influence.