Application of SPC

The application of SPC involves three main phases of activity:

• Understanding the process and the specification limits.
• Eliminating assignable (special) sources of variation, so that the process is stable.
• Monitoring the ongoing production process, assisted by the use of control charts, to detect significant changes of mean or variation.

Understanding the Process

How you setup your SPC solution will be dependent on your process, the specification limits, the source of the SPC data and the type of process control you need. The SPC module provides a flexible solution that allows you to build the SPC solution you need.

You'll want to be able to answer the following questions in order to be able to determine how to implement the solution:

• What process variables do we need to measure?
• How many measurements will we take?
• How and where do we get the data?
• When and how often do we sample?
• Who can enter samples?
• What kind of control charting do we need?
• What kind of control limits do we need?
• What type of analysis do we need to provide?
• Where do we get the specification limits from?
• What type of controls do we need to put into place?

Ideally, your process engineer or QA department has provided you with these detailed requirements, but if not, here's a link to a handy Guide to Control Charts that may help you select the most appropriate Chart for your application.

Monitoring the Process

The data from measurements of variations at points on the process map is monitored using control charts. Control charts attempt to differentiate assignable (special) sources of variation from common sources. Common sources are an expected part of the process and are of less concern to the manufacturer than assignable sources. Using control charts is a continuous activity, ongoing over time.

When the process no longer triggers any of the control chart detection rules, it is said to be stable. A process capability analysis may then be performed on a stable process to predict the ability of the process to produce conforming product in the future.