Do you know that Statistical Process Control (SPC) is one of the industry’s oldest quality tools?

In the 1920s, Dr Walter Shewhart developed the control chart for Bell Laboratories and published Shewhart’s book Statistical Method from the Viewpoint of Quality Control (1939). The tool was widely used in supporting armoury production during World War.

During the war, the resources (e.g. Time, Money and Labor) are limited. Hence, quality control through 100% production inspection is a kind of luxury to businesses.

Therefore, inspection through sampling is the only option left behind as the most economical method for quality control.

However, to ensure the samples are reliable to represent the total population, SPC is the tool that can diagnose whether the process is stable and in control during the period or not.

SPC Today

Nowadays, quality control might be not an issue for big corporations. Thanks to advanced technology, we can expedite and lower the quality control cost via advanced machines such as laser calibrators etc.

SPC and Process Capability

However, SPC still plays a significant role in sustaining high-quality results regardless of production or transaction. Its main functions are to identify whether the process is in control, which will affect the long-term process capability (Ppk).

When calculating the process capability, theoretically, the long-term process capability will shift at 1.5 sigma level or ~0.5 if you use Cpk Ppk measurements.

If you find a big gap between short term and long-term process capability, it is most likely affected by an out-of-control and unstable process. These situations can be diagnosed using tests in SPC.

Therefore, the SPC is also critical to identifying potential probability in sustaining good results in the process for the long term. But always remember, if you’re getting good results from SPC only does not shows that you are meeting the customer’s specifications. Thus, SPC and Process Capability are the tools that always complement each other.

Learn more about the analysis using Statistical Process Control in our signature Statistical Process Control and Quality Tools courses.