Overview for Normal Capability Sixpack

Use Normal Capability Sixpack to assess the assumptions for normal capability analysis and to evaluate only the major indices of process capability. Using this analysis, you can do the following:

  • Determine whether the process is stable and in control
  • Determine whether the data follow a normal distribution
  • Estimate overall capability (Pp, Ppk) and potential capability (Cp, Cpk)

To perform the analysis, you must specify a lower or upper specification limit (or both) to define your process requirements. The analysis evaluates the spread of the process data in relation to the specification limits. When a process is capable, the process spread is smaller than the specification spread. The analysis can also indicate whether your process is centered and on target. In addition, the analysis estimates the proportion of product that does not meet specifications.

For example, a quality analyst wants to evaluate the capability of a bolt manufacturing process. To satisfy customer requirements, the thread length of the bolts should be within 0.5 mm of the target of 20 mm. The analyst uses normal capability sixpack to quickly assess main capability indices and evaluate the assumptions for normal capability analysis.

Where to find this analysis

To perform normal capability sixpack, choose Stat > Quality Tools > Capability Sixpack > Normal.

When to use an alternate analysis

  • If you want to evaluate a more complete set of capability measures, in addition to the major indices, use Normal Capability Analysis.

  • If you want to evaluate the assumptions for using nonnormal capability analysis, use Nonnormal Capability Sixpack.

  • If your process produces large variation between subgroups, such as a batch process, use Between/Within Capability Sixpack to assess the assumptions for a between/within capability analysis.