Another type of capability index, Cpm, is much less known and used less frequently than Cpk or Ppk. The main difference between the Cpm and the other capability indices is that the bias from the target, not mean, is directly taken into consideration in the Cpm. The bias is the difference between the process average and the target.
Continue reading “Cpm”Category: SPC & 6 sigma
Cp, Cpk, Pp, Ppk
Process capability, Cp, tells how well a process meets customer’s specifications. It is defined as the ratio of engineering tolerance (USL – LSL) to the natural tolerance (-3σ to 3σ) . However, a process can be capable of meeting specifications, but not be meeting specifications if the process is not centered relative to the specifications. Therefore, process capability index, Cpk, is introduced to take into account of the centeredness.
Continue reading “Cp, Cpk, Pp, Ppk”