Deck 4 Flashcards
When do you use Cpk?
After a process has reached statistical control
When do you use Pp and Ppk?
when you are setting up your process
Define “specification spread”
The difference between the specified Lower Specification Limit (LSL) and specified Upper Specification Limit (USL)
What is another name for specification spread
The voice of the client
Define “process spread”
The distance between the highest value generated and the lowest value generated.
NOT USL and LSL - which would be specification spread
What is another name for “process spread”?
The “Voice of the Process”
What does Pp measure?
Process Capability
What is the formula for calculating process capability?
Pp = (USL – LSL) / 6 * s
What is a ‘Good’ Process Capability (Pp) Number?
a Pp of above 1.5
because that would reflect a process with less than 3.4 DPMO
What USL – LSL is required to reach σ quality standard of 3.4 DPMO?
12
What does the “s” stand for in Pp = (USL – LSL) / 6* s?
Standard deviation
What does a Ppk of 1 mean?
that your process is completely centred.
there is “half of a bell curve” between the center of the process and the nearest specification limit
How can Ppk be determined using the “z” score?
Divide the “z” score by 3
What is the “z” score?
Z score measures how many standard deviations a value (x) is from the population mean (µ).
If the Z value is positive, it indicates that the value or score (x) is above the mean. Similarly, if the Z value is negative, it means the value (x) is below the mean.
What is a “z” score
the number of standard deviations a value (x) is above or below the mean.
