I would say that an unilateral is indeed possible to calculate by using Cpk=CpU og Cpk=CpL depending on which side the tolerance is.
The issue must be that it will not reflect the direction of the distance, and it that sense it will not really evaluate the process:
Example:
Part #1 X1.0 Y0
Part #2 X-1.0 Y0
Part #3 X0 Y1.0
Part #4 X0 Y-1.0
Same distance from nominal will give a high (infinite) Cpk Value, but is the process stable?
Not really since the direction is different.
I would say that an unilateral is indeed possible to calculate by using Cpk=CpU og Cpk=CpL depending on which side the tolerance is.
The issue must be that it will not reflect the direction of the distance, and it that sense it will not really evaluate the process:
Example:
Part #1 X1.0 Y0
Part #2 X-1.0 Y0
Part #3 X0 Y1.0
Part #4 X0 Y-1.0
Same distance from nominal will give a high (infinite) Cpk Value, but is the process stable?
Not really since the direction is different.
