SPC stands for Statistical Process Control. It is a methodology that is widely used to continuously improve processes, and is a subset of Six Sigma. Six Sigma, one of the major techniques of Lean manufacturing, aims to prevent process variation and make sure that a company has the ability to consistently and reliably produce products and services that are of high quality. SPC is a vital strategy used during Six Sigma to assess process control and monitor variations. Ultimately, it aids in decision-making to eliminate variations and reduce waste, ensuring that processes operate as efficiently as possible.
SPC & Control Charts
SPC is typically associated with two tools: control charts and Design of Experiments (DOE). DOE is a method that allows people to investigate multiple causes of variation simultaneously, while control charts are a means to monitor an ongoing production process and identify variation. There are two types of process variation: 
- Common cause variations, which are considered to be naturally occurring and can be expected to happen within a process. These variations are “in control.”
- Special cause variations, which are not natural and are externally sourced. These are “not in control,” and reducing this kind of variation is the key to creating more efficient operations.
SPC is applied in three phases. First, the process and its specification limits are fully understood. Then, the process is stabilized to eliminate causes of variation. Lastly, ongoing process is observed and variation is detected. The ultimate aim to Statistical Process Control is to separate common cause variation from special cause variation in a process. Once it’s determined which variations are natural, and which ones are not, it becomes possible to eliminate special cause variation. Because common cause variation is to be expected, it cannot be eliminated, but may be reduced.
As part of Six Sigma, SPC is a methodology that monitors and continuously optimizes a process. It can help ensure that products are of high quality, wastes in production are eliminated, and that the likelihood of a finished product being scrapped is reduced.
