CQI flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Inch to millimeter conversion

One inch equals exactly 25.4 millimeters, so multiply inches by 25.4 to obtain millimeters and divide millimeters by 25.4 to obtain inches.

Cp process capability index

Cp equals the specification width (USL minus LSL) divided by six times the process standard deviation. It measures potential capability and ignores how well the process is centered.

Cpk process capability index

Cpk equals the smaller of (USL minus the mean) or (mean minus LSL), divided by three sigma. It accounts for process centering and is never larger than Cp.

Pythagorean theorem

In a right triangle the square of the hypotenuse equals the sum of the squares of the two legs, written as a squared plus b squared equals c squared.

Area of a circle

The area equals pi times the radius squared, or equivalently pi times the diameter squared divided by four, where pi is approximately 3.14159.

Mean median and mode

The mean is the arithmetic average of the data, the median is the middle value when data are ordered, and the mode is the most frequently occurring value.

Sample standard deviation formula

The sample standard deviation is the square root of the sum of squared deviations from the mean divided by n minus one, using n minus one degrees of freedom.

Degrees to radians conversion

Multiply the angle in degrees by pi and divide by 180 to obtain radians; 180 degrees equals pi radians and 90 degrees equals pi divided by two.

Traceability in measurement

An unbroken chain of comparisons, each with a stated uncertainty, linking a measurement result to national or international measurement standards.

Accuracy versus precision

Accuracy describes how close a measured value is to the true value, while precision describes how closely repeated measurements agree with each other.

Gage repeatability and reproducibility

Repeatability is variation from repeated measurements by one appraiser with one instrument; reproducibility is variation between different appraisers using the same instrument and parts.

Ten to one rule

A measuring instrument's discrimination should be no more than one tenth of the tolerance being verified, so that gage error contributes negligibly to the accept or reject decision.

Thermal expansion of steel

Steel expands about 6.5 microinches per inch per degree Fahrenheit, or about 11.7 micrometres per metre per degree Celsius, so dimensional measurements are referenced to 20 degrees Celsius.

Micrometer least count

A standard inch micrometer with a 40-thread-per-inch screw and a 25-division thimble reads to 0.001 inch; metric versions commonly read to 0.01 millimetre.

Type A and Type B uncertainty

Type A uncertainty is evaluated statistically from repeated observations; Type B uncertainty is evaluated by other means such as calibration certificates, manufacturer specifications, or engineering judgement.

Sine bar angle formula

The sine of the angle equals the height of the gage block stack divided by the sine bar length, so the angle is the arcsine of height over length.

NDT penetrant testing

A liquid penetrant is applied to a cleaned surface and drawn out of surface-breaking discontinuities by a developer, revealing cracks in nonporous materials.

Magnetic particle inspection

Ferromagnetic parts are magnetized and iron particles are applied; particles collect at surface and near-surface discontinuities where magnetic flux leaks from the part.

Ultrasonic testing

High-frequency sound waves are transmitted into a part and reflections from internal boundaries or flaws are displayed, allowing detection of internal discontinuities and thickness measurement.

Radiographic testing

X-rays or gamma rays pass through a part and expose film or a detector; differences in absorption reveal internal voids, inclusions, and density variations.

Acceptable quality level

The AQL is the maximum percentage of nonconforming units that, for sampling purposes, is considered acceptable as a process average.

Operating characteristic curve

An OC curve plots the probability of accepting a lot against the lot fraction nonconforming, showing producer and consumer risk for a given sampling plan.

Producer and consumer risk

Producer's risk, alpha, is the probability of rejecting a good lot; consumer's risk, beta, is the probability of accepting a bad lot.

First article inspection

A complete verification of the first production part against all drawing and specification requirements, confirming that the process can produce conforming product.

Quality assurance versus quality control

Quality assurance focuses on preventing defects through planned processes and systems, while quality control detects defects by inspecting and testing products against requirements.

Corrective versus preventive action

Corrective action eliminates the root cause of a detected nonconformity so it does not recur; preventive action addresses potential causes before a nonconformity occurs.

Control chart common cause

Common-cause variation is the inherent, stable variation of a process in statistical control; it is reduced only by changing the process itself, not by adjusting individual points.

Control limits versus specification limits

Control limits are calculated from process data at plus and minus three standard deviations and describe what the process does; specification limits come from the customer and describe what is required.

Pareto principle

Roughly 80 percent of problems come from about 20 percent of causes, so improvement effort should target the few highest-frequency categories shown on a Pareto chart.

Five whys technique

Repeatedly asking why a problem occurred, typically five times, drills past symptoms to the underlying root cause so that corrective action addresses the true cause.

Cost of poor quality

Prevention, appraisal, internal failure, and external failure costs; failure costs, especially external ones, are usually the largest and are reduced by investment in prevention.

Third-party audit

An audit performed by an independent organization not employed by the auditee, typically for certification or registration to a standard such as ISO 9001.