Guidelines for Statistical Process Control

The language of ISO 9001:2000 is less manufacturing oriented for the benefit of its readers in the software and service sectors. As a result, “statistical techniques” seem to have been relegated to a lesser role.

The old clause 4.20 in ISO 9001:1994 was entirely devoted to Statistical Techniques. Now the techniques are only mentioned in clause 8.1 of ISO 9001:2000 as possible methods for process monitoring, measurement, analysis, and improvement.

However, look more closely. Clause 4.1 (c) requires determining the criteria and methods for effectively operating and controlling your processes. Clause 4.1 (e) requires process monitoring, measurement, and analysis.

Clause 7.1 (c) requires you to plan your verification, validation, inspection, and test activities, as well as, determine your product acceptance criteria. Clause 8.1 requires the use of applicable methods (including statistical techniques) to demonstrate product conformity, ensure system conformity, and continually improve the effectiveness of the system. Don’t overlook that clause 8.2.3 requires process monitoring and clause 8.2.4 requires monitoring and measurement of product characteristics.

So, if you want to implement statistical techniques, where can you turn for advice? See ISO 11462-1:2001, Guidelines for Implementation of Statistical Process Control (SPC) — Part 1: Elements of SPC.

ISO 11462-1 can help you define your SPC goals, for example, to reduce process variation, predict process behavior, and quantity process capability. It also describes the conditions that must be present for a successful SPC system. Management must use the data to react to process disturbances and make improvement decisions.

Section 7 of ISO 11462-1 addresses the key elements of an SPC system. Some of these elements are:

Plan: (7.1) process documentation and control plans; (7.2) process targets and limits; (7.3) measurement system evaluation

Do: (7.6) data recording and collection; (7.12) process output monitoring; (7.13) process control system

Check: assessments of short-term (7.14) and long-term (7.15) variability; (7.16) communication of process analysis results

Act: (7.20) process improvement, optimization, and troubleshooting

Support: (7.4) work instructions; (7.9) process sequence; (7.10) process logs; (7.5) employee training; (7.19) project teams

For more information, read the on-line Quality Digest article: “Do You Know Your SPC“.