What should an SPC procedure contain?

Knowing that all production processes have some variation, about 100 years ago Walter Shewart discovered a way to distinguish between common causes and special causes of variation in a process. Shewart also understood the danger of "firefighting" actions to react and act depending on where individual values ​​are located in relation to the tolerances of a process.

This discovery of Walter Shewart, together with the methods developed later, is today called statistical analysis of a process (SPC).

So why should we use SPC? The answer is simple, to save or earn more money from our business, in one form or another:

• tracking the stability of the process indicates the occurrence of special causes and we can react before the occurrence of defects, saving money
• the high capacity of a process reduces the need for final inspection, saving money
• the good quality of the products obtained after using SPC will be noticed and appreciated by customers, which will lead to earning more money for our business

Should we also have an SPC procedure?

It should be noted that the existence of this procedure is not mandatory according to the IATF 16949 standard, but it helps organizations to understand very clearly:

• what statistical tools should be used and how
• what knowledge is required to understand and use these statistical tools (see 9.1.1.2 and 9.1.1.3 in IATF 16949).

The use of statistical tools being an activity with a preventive role, must be started as soon as possible in the life cycle of a product. The SPC procedure should describe, among others:

• the use of statistical tools since the time of the APQP, for the realization of the D / PFMEA and of the corresponding Control Plans
• Use in series production
• data collection methods, manually or automatically
• frequency and size of data samples collected, depending on the situation
• analysis and management of collected data - who, when and what to do with this data

Over the years, we have encountered different approaches to clients, from total lack of use, to non-unitary application (the procedure was missing or not known) but also, we had the pleasure to see the correct use and not just because the customers asked for it 😊.