Statistical Process Control (SPC) Flashcards
7 cards from real Lean Six Sigma Black Belt Certification practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Statistical Process Control (SPC) flashcards as text
A process has a Cpk of 0.85. What does this indicate?
Answer: The process is not capable of meeting specifications
A Cpk below 1.0 indicates the process is not capable of consistently meeting specification limits.
Which Western Electric rule is violated when 2 out of 3 consecutive points fall beyond 2 sigma on the same side of the centerline?
Answer: Rule 2
Western Electric Rule 2 flags 2 out of 3 consecutive points beyond 2 sigma on the same side as a signal of special cause.
What is the primary purpose of the CUSUM chart?
Answer: Detect small, sustained shifts in the mean over time
CUSUM (Cumulative Sum) charts are specifically designed to detect small, sustained process mean shifts that Shewhart charts may miss.
In an np-chart, what does 'n' represent?
Answer: Constant subgroup size
In an np-chart, 'n' is the constant subgroup size; the chart plots the count of nonconforming items using a fixed sample size.
Which measure describes the within-subgroup short-term variation used to estimate sigma in control chart calculations?
Answer: Average range (R-bar)
The average range (R-bar) captures within-subgroup variation and is used to estimate the short-term process standard deviation for control limit calculations.
A team notices a gradual upward trend of 7 consecutive points on an X-bar chart. Which type of special cause is most likely?
Answer: Tool wear or process drift
A sustained upward trend on a control chart typically indicates process drift, often caused by tool wear, gradual equipment degradation, or consumable depletion.
What does the d2 constant used in control chart formulas represent?
Answer: A factor that converts the average range to an estimate of sigma
The d2 constant is a bias correction factor that converts R-bar to an unbiased estimate of the process standard deviation (sigma-hat = R-bar / d2).