Nndifference between cp cpk pdf

Process capability cp, cpk and process performance pp. How critical the measured process is to downstream processes. Pdf process capability and capability index cp and cpk. Cp and cpk consider the deviation mean within rational subgroups, while pp and ppk set the deviation based on studied data. In a perfectly centered data set, there will be no difference between cp and cpk. The difference between cp and cpk and when they are used. But the statistical measurements of cp, cpk, pp, and ppk may provide more insight into the process.

The demand must be realistic and it should be certain that it is viable and the process is capable of achieving it. The main difference between pp and cp on one side and ppk and cpk on the other side is whether we use complete set of data for calculation pp and ppk where we calculate real performance of the system, or we use sample preproduction, batch, logical subgroups where we calculate capability of the process. The difference between cp and pp, as well as between cpk and ppk, results from the method of calculating standard deviation. Process capability and capability index cp and cpk. Process capability example,how to calculate cp and cpk. This will help set realistic goals and aid in avoiding unnecessary pressure to the bodies involved in the process. It is worth working with more conservative pp and ppk data in case it is unclear if the sample. In any industry, understanding the true potential of a process is vital. The difference between cp and cpk shows that as well as being able to indicate the capability of the process to produce within specification, in cpk, there is an indication of the ability of the process to conform to the target value. Think of throwing darts at a dart board and having the center of the bulls eye be the 0,0 on a cartesian plane and the edges being out 3 units from that center point we will use the edge of the dart board or 3 and 3 as our usl and lsl. Learn the definitions, interpretations and calculations for cp, cpk, pp and ppk. Unlike the cp, the cpk is measured using standard deviation, specification limits and mean.