A method of using statistical techniques to monitor and control processes by tracking variation over time.
SPC uses statistical methods to monitor process variation and identify signals that need investigation. It supports process control but does not guarantee stability or product conformity.
Metrics like process capability indices summarize how well a process fits within specification limits.
Setting up SPC
Teams choose the right chart type: X-bar, R, p-chart, or c-chart: based on the data and sampling strategy.
They calculate control limits from historical data and update them when processes change materially.
Responding to signals
Rules such as the Western Electric criteria help teams spot unusual patterns: a sudden spike, a slow drift, or a run of points on one side of the average: that need investigation before defects reach the customer.
Follow the reaction plan when a signal occurs. Check affected production and avoid adjusting machines in response to ordinary random variation.
Key takeaways
- SPC distinguishes normal variation from signals that need action.
- Control limits and rules guide timely response.