Process Capability (Cp & Cpk) (Pp & PpK) Process capability is the ability of process to meet the requirement's set for the process i.e. to do particular work without producing or producing less defects Cp and Cpk are called Process Capability. Pp and Ppk are called Process Performance. In both cases we want to try to verify if the process can meet to meet Customer CTQs (requirements) Process capability – Cp : This is defined as the tolerance width divided by the total spread of process (6 Sigma) Cp indicates the spread of variation present in a process Process capability is the ability of process to meet the requirement's set for the process i.e. to do particular work without producing or producing less defects One way to determine process capability is to calculate capability indices. Capability indices are used for continuous data and are unit less statistics or metrics Cp :- It is the potential capability indicating how well a process could be if it were centered on target. This is not necessarily its actual performance because it does not consider the location of the process, only the spread. It doesn't take into account the closeness of the estimated process mean to the specification limits. Cp indices recognize the fact that your samples represent rational subgroups, which indicate how the process would perform if the shift and drift between subgroups could be eliminated. Therefore, it calculates the process spread using within-subgroup variation Cpk :-Measures of potential process capability, calculated with data from the subgroups in your study. They measure the distance between the process average and the specification limits, compared to the process spread: CPL measures how close the process mean is running to the lower specification limit CPU measures how close the process mean is running to the upper specification limit Cpk equals the lesser of CPU and CPL Process is centered – Cp Process is not centered - Cpk How to calculate Cpk? How to calculate Cpk using Z value ? Cpk can be determined by dividing the Z score by three. A z score is the same as a standard score; the number of standard deviations above the mean. How to read Z table How to calculate Cpk using Z value ? What are Good Values for Cpk? Remember the Car parking in the garage analogy? Cpk = Negative number: Your process will regularly crash the car into the wall Cpk =0.5: You have a good chance hitting the wall on entry Cpk =1: Your car may be just touching the nearest edge of the entry Cpk =2: Great! You have great clearance. You could double the width of your car before you hit the side of the garage Cpk =3: Excellent! You have excellent clearance. You could triple the width of your car before you hit the side of the garage The Cp index is calculated using specification limits and the standard deviation only. This index indicates, in general, whether the process is capable of producing products to specifications. No information on the ability