OK - I worked out the Cp and Cpk values for the data you sent. it is in the attached excel file. I assume that hyou now understand that your formula for Cp was wrong - you were not including the standard deviation.
In general if you look at the histogram of your data there are parts that are out of spec on both sides of the tolerance range. Your process is also not centered. The average is higher than the target.
Cp is a simple ratio of the actual process spread (6*SD) to the tolerance (USL-LSL) (as if it were centered)
Cpk takes the location of the process relative to the tolerance into account in addition tot eh spread vs the tolerance range.
Therefore, unless the process is perfectly centered Cp (aka process potential) will always be greater than Cpk (aka process performance).
Please be advised that this topic is quite complex and I suggest that a few searches for past discussions here will be very helpful in increasing your understandign of the topic...rest assured that you are not the only one who has had these questions and/or who has had less than stellar training...
In general if you look at the histogram of your data there are parts that are out of spec on both sides of the tolerance range. Your process is also not centered. The average is higher than the target.
Cp is a simple ratio of the actual process spread (6*SD) to the tolerance (USL-LSL) (as if it were centered)
Cpk takes the location of the process relative to the tolerance into account in addition tot eh spread vs the tolerance range.
Therefore, unless the process is perfectly centered Cp (aka process potential) will always be greater than Cpk (aka process performance).
Please be advised that this topic is quite complex and I suggest that a few searches for past discussions here will be very helpful in increasing your understandign of the topic...rest assured that you are not the only one who has had these questions and/or who has had less than stellar training...
