SPC Process Variation & Capability 2

Question 1

A process has a Cpk of 0.85. What does this indicate about the process?

Accepted Answer

The process is not capable and may be producing defects

Answer

A Cpk below 1.0 indicates the process is not capable and is likely producing output outside specification limits.

Question 2

Which type of variation is represented by a single point falling outside the control limits on an X-bar chart?

Accepted Answer

Special cause variation

Answer

Points outside control limits are a signal of special cause (assignable cause) variation that requires investigation.

Question 3

The Pp index differs from Cp in that Pp uses:

Accepted Answer

The overall standard deviation of all collected data

Answer

Pp uses the overall standard deviation calculated from all data points, while Cp uses the short-term within-subgroup estimate.

Question 4

In a process capability study, what does the 'voice of the customer' refer to?

Accepted Answer

The specification limits set by customer requirements

Answer

The voice of the customer is represented by specification limits (USL and LSL) that define acceptable product boundaries.

Question 5

If USL = 50, LSL = 30, and the process mean is 38, which formula gives the correct Cpk?

Accepted Answer

min[(50-38)/3σ, (38-30)/3σ]

Answer

Cpk is the minimum of the upper and lower capability ratios, reflecting the worst-case distance to either spec limit.

(SPC) Statistical Process Control Certification Practice Test