Use Normal Capability Analysis to evaluate the potential (within) and overall capability of your process based on a normal distribution. Using this analysis, you can do the following:
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 0.1 mm of the target of 20 mm. The analyst uses a normal capability analysis to evaluate how well the process meets the specifications of 20 ± 0.1 mm, based on a normal distribution of the data.
This analysis includes transformation functions to transform nonnormal data to fit a normal distribution.
To perform normal capability analysis, choose .
If you do not know whether your process data are in control or whether they can be evaluated using a normal distribution, use Normal Capability Sixpack to assess these assumptions before you use this analysis.
If your data are nonnormal and you want to evaluate process capability by fitting a nonnormal distribution, rather than by transforming your data, use Nonnormal Capability Analysis.