Industrial Statistics with Minitab

16.3 Diameter_capability_2

During the series production of the previous part, each day, after adjusting the machine, 50 parts are consecutively produced and later a capability study is carried out with them to assure that the adjustment was done correctly.

The 50 values used for the capability study on a particular day are stored in the file DIAMETER_CAPABILITY_2.MTW. Is everything correct?

Proceed to carry out a capability study going to:

Stat > Quality Tools > Capability Analysis > Normal

In the dialog box, it is only necessary to indicate that the data are in the Single column: C1, that the Subgroup size is 50, and that the specification limits are 7.4 and 7.6.

Everything appears correct in the graphical output of the capability study. Also, it is important to analyze whether there is any tendency among the data. In this case, we cannot use Capability Sixpack since only one single point is shown on the control graph (there is only one sample of size 50). Thus, it is more appropriate to make a control graph for the individual observations, as shown below.

Stat > Control Charts > Variables Charts for Individuals > Individuals

In the above graph, nothing in particular is observed. Hence, the production can be started.