Any time I hear the word ‘inspection‘, I think failure. An inspection is an admission that you haven’t been able to build quality into a production process.
That said, I think there is a place for inspections, as long as there is recognition that they wasteful. But since even wasteful processes can be improved, here’s a simple trick that can test if you are giving your inspectors enough time to find all the defects coming off your line.
Without telling the inspectors, quarantine some inspected product. The units can be randomly selected, or they can be everything that was produced in a particular time period. Whichever method you choose, though, be sure to prevent bias into the choice of products. For example, if you choose the latter, be sure that it is a representative time period—not a slow or busy period that could skew the results of the test.
Also, make sure that when you get the products isolated, you are able to identify which ones failed the inspection initially—they might have been reworked and will pass the second time through. Finally, make sure that the sample size is big enough to have faith in its statistical significance.
Once the products are segregated, ask the inspectors to look them over again with no time constraints. Give the inspectors all the time they need to thoroughly inspect the products a second time.
Here’s a key point to make sure you communicate well. This is a test of management, not of the inspector. Make sure the inspector feels comfortable that this exercise is to see if they are being given enough time to do their job, not to see how well they are doing their job.
Once the reinspection is done, compare the quality results to the initial testing. Remember to include any reworked products as failures, even if they passed this time around.
If the number of defects found in the quarantined pile is similar to the number identified coming off the line, your inspector probably has enough time. If not, you are short-staffed, and your quality is probably suffering as a result.
Again, the right way to resolve this problem is to build quality into the process with poka yokes. Absent that approach, at least make sure you inspectors are given the opportunity to get the job done right.
If you try this approach out, or have tried it out in the past, I’d love to hear what you discovered.