In machining processes, for geometrical parameters what should be the Cpk/Ppk requirement?

Ppk = 1.67 Short term capablity 

Cpk = 1.33 Long term capablity

 in line production that required cpk>=1.67,ppk>=1.37

Cp/Cpk represents short-term process quality where for a process to be JUST capable then Cp MUST BE >1, If Cp=Cpk then the process is centred BUT due to process drift then for a process to be sonsistently capable then Cp must to much greater than 1 (for example between 1.6 to (ideally 2). So if Cp = 2 and Cp=Cpk the process is centred and is very capable. Pp/Ppk measures similar parameters to Cp/Cpk but is longer term process capablity.

Equal to or more than 1.33

In machining process, Cpk requirement should be equal or more than 1.33.

According to AIAG , CpK >1.33 and Ppk > 1.67

1. FOR PPK IT SHOULD BE MORE THAN 1.67

2. FOR CPK IT SHOULD BE MORE THAN 1.33

Should be lesser ot greter than 1.66

In machining process, the value of Cpk should be between 1.67 to 2 and will always smaller than value of Cp 

During machining process, Cpk ad ppk should have more than or equal to the 1.66 value required to the geometric dimensions