You can’t “inspect quality” into a product

A company thought that they would try to have a component manufactured in Japan on a trial basis. As part of the qualification activities, the company clearly wrote that they would accept only three rejects per 10,000 parts.

When the delivery came from Japan, they found two boxes accompanied by a letter from the Japanese firm.

“Dear Sir/Madam,

We are having a hard time meeting your requirements. We had to manufacture the three defective parts separately to meet your requirements. See enclosed.”

The second, much smaller box, was clearly labelled “THREE REJECTS AS REQUIRED. DO NOT USE FOR PRODUCTION.”

Of course, this anecdote may not be true but it highlights a widespread belief that quality can be “inspected into” a product. Also, that human inspection can accurately detect quality levels of product entering or leaving a process.

Juran, one of the giants of Quality, has written that, based on his studies performed on inspector accuracy, 100% inspection is about 87% effective. Using his formula, even triple layers of inspection will result in 0.3% escapes. Of course, that assumes that each Inspector behaves as if theirs is the only inspection. In reality, if inspectors are aware that other inspections are happening, they are likely to feel more relaxed, possibly allowing more defects to slip through.

So don’t rely on inspection to catch everything at the end of the process. Do as the Japanese firm did and build inspection into each task so that when errors or defects occur, there is immediate feedback given to the most important person. Better still, pursue mistake-proofing (Poka-Yoke) throughout the process.