Mixed Deck — All SPC Topics Flashcards

A process with high Cpk but frequent customer complaints most likely suffers from:

Answer: Specification limits set too wide relative to actual customer needs

If Cpk is high but complaints occur, the specification limits may be wider than what customers actually need, masking true quality problems.

The 'R chart' in an X-bar and R control chart monitors:

Answer: The range (spread) within each subgroup

The R chart tracks the within-subgroup range to monitor process variability over time.

If a process has Cpk = 1.0, what percentage of output is expected to be within specification?

Answer: 99.73%

A Cpk of 1.0 corresponds to the process mean being exactly 3 sigma from the nearest specification limit, yielding 99.73% within spec.

Which control chart is best suited for monitoring a short-run production environment where part numbers change frequently?

Answer: Standardized (Z) chart

Standardized (Z) charts convert measurements to Z-scores relative to each part's target and tolerance, allowing multiple part types to be plotted on a single chart.

A rule of thumb in MSA states that an instrument's resolution should be no greater than what fraction of the process variation or tolerance?

Answer: 1/10

The AIAG MSA Reference Manual recommends that the measurement increment (resolution) should be no larger than one-tenth (1/10) of the process variation or tolerance to avoid masking real differences.

A process producing 3.4 defects per million opportunities operates at what sigma level?

Answer: 6 sigma

Six Sigma quality is defined as 3.4 DPMO, which accounts for a 1.5-sigma long-term shift in the process mean.

What is the significance of peer review in materials science & specifications for SPC professionals?

Answer: It promotes accountability, knowledge sharing, and quality improvement

Peer review promotes accountability, knowledge sharing, and quality improvement by allowing SPC professionals to benefit from collective expertise and identify areas for growth.

A Pareto chart is used during data interpretation to:

Answer: Identify the vital few defect categories that account for most problems

A Pareto chart ranks defect categories by frequency to apply the 80/20 rule and focus improvement efforts on the most significant issues.

Which measure of central tendency is LEAST affected by extreme values in a dataset?

Answer: Median

The median is a positional measure that is resistant to outliers, unlike the mean which is pulled toward extreme values.

What is the significance of peer review in quality control & inspection methods for SPC professionals?

Answer: It promotes accountability, knowledge sharing, and quality improvement

Peer review promotes accountability, knowledge sharing, and quality improvement by allowing SPC professionals to benefit from collective expertise and identify areas for growth.

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

Answer: Special cause variation

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

When a process is 'in statistical control' but not capable, the correct management action is to:

Answer: Redesign or improve the process to reduce inherent variation

An in-control but incapable process has stable but excessive common cause variation that requires fundamental process improvement, not reaction to individual points.

Which of the following is an example of an assignable (special) cause detected during data review?

Answer: A single measurement exceeding the upper control limit after a tool change

A point outside the control limits linked to an event like a tool change is a special cause that requires investigation and corrective action.

When comparing Ppk to Cpk for the same dataset, Ppk will typically be:

Answer: Lower than or equal to Cpk because it uses total variation

Ppk uses overall standard deviation (larger, including between-subgroup variation), making it equal to or lower than Cpk which uses the smaller within-subgroup estimate.

The CUSUM chart is particularly sensitive to detecting:

Answer: Small, sustained shifts in the process mean (0.5–1.5 sigma)

CUSUM (Cumulative Sum) charts accumulate deviations from a target and excel at detecting small, persistent mean shifts that traditional Shewhart charts often miss.

According to AIAG guidelines, a Gauge R&R %Study Variation below what threshold is generally considered acceptable?

Answer: 10%

Per AIAG MSA guidelines, a %Study Variation below 10% is acceptable; 10–30% may be acceptable depending on circumstances; above 30% the measurement system needs improvement.

Which control chart is most appropriate for monitoring the number of defects per unit when the subgroup size varies?

Answer: u chart

The u chart monitors the average number of defects per unit and accommodates varying subgroup sizes.

What distinguishes a u-chart from a c-chart?

Answer: u-chart allows variable inspection area; c-chart requires constant area

The u-chart expresses defects per unit and accommodates variable inspection areas or subgroup sizes, whereas the c-chart requires a constant area of opportunity.

What does Cpk take into account that Cp does not?

Answer: Process centering

Cpk measures process capability while considering how centered the process is between the specification limits.

How should a SPC professional handle a situation where quality control & inspection methods protocols conflict with practical constraints?

Answer: Document the conflict and seek guidance from appropriate authorities

When protocols conflict with practical constraints, the professional approach is to document the conflict and seek guidance, ensuring transparency and compliance while working toward a resolution.