In manufacturing, process consistency is key. But consistency can be elusive— after all, variables that cause variation can be endless. Unfortunately, variation inevitably leads to defects.

That’s why the right monitoring system matters.

When a process is stable (or is within statistical control), that means that quality personnel have removed all sources of variation, leaving only common, predictable (aka preventable) causes. To determine this state of stability, quality leaders use control charts. They put control limits in place and when the charts show no variation beyond those limits, the process is considered stable.

How a capability analysis can help

Yet, an in-control process may not necessarily meet specification requirements.

A capable process, however, always meets specifications, or internal goals. A process meets this description if virtually all its output is within spec. To ensure that a stable process is capable, quality personnel can redesign their process.

So, how can you tell if a process is capable before you wind up with defects?

You perform a capability analysis.

Quality leaders can use capability analyses, or statistics, to determine if a system can meet needed requirements. Quality personnel essentially use software to determine if control chart data is statistically stable. Fluctuations in data will reveal, through indices, a sampling of past variation if the process is not stable. If, however, a system is stable, the capability analysis may predict the system’s future performance.

Quality leaders looking to improve their processes can monitor their data over time to see how their systems are changing.