Below is a sample chart with interpretation underneath.
This is a sample of a 4 cavity system. The test parameter is weight.
Looking at the range chart, all cavities are within the control limits and therefore pass.
On the average chart, there is a problem with cavity #2. It is above the control limits and therefore does not pass. Do no be fooled by the relatively high cpk value of 2.635. Because each subgroup consists of only one cavity, the cpk value is usually high. That does not imply that your process is within the control limits. All we are looking for here is to determine if all cavities are statistically the same so that we can take just one cavity as a sample for any subsequent tests. In the case above, reduce the weight on cavity #2 and run the test again
Next month I will show the steps to test if your process is in control.