Product Maturity, Volume 2

1Sampling in Manufacturing

Chapters 1 to 6 of Volume 1 described various methods for building maturity. However, from a manufacturing perspective, these methods must be cost-effective. One of the solutions that can be considered to reduce costs is to test less than 100% of the products before delivery to the system manufacturer. This is called sampling.

As expected, there are various standards dealing with this subject, such as ISO 28590. These standards clarify the sampling rules to be applied, and the interested reader is invited to read them for further details.

However, the standards do not cover several aspects that are very important for the manufacturer:

• – The cost aspect, which leads to the following questions:
  • - What is the benefit of applying a sampling rule?
  • - Is a sampling rule adapted for my application?
  • - What rule should I use to minimize costs?
• – What is the impact of test coverage rates if they are not 100%?
• – What is the impact of considering a distribution of potential defects?

This chapter aims to suggest a solution for each of these cases in order to formulate optimum sampling in terms of quality and cost.

Theoretically speaking, sampling techniques rely on discrete probability distributions (the random variable can only take certain values), unlike the probability distributions for estimating the reliability of a failure mechanism, which are continuous (e.g. exponential, Weibull, etc.). The Bernoulli distribution is used for the result of a test (failure ...