17 terms

Process capability

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Assignable variation
Deviation in the output of a process that can be clearly identified and managed.
Common variation
Deviation in the output of a process that is random and inherent in the process itself.
Upper and lower specification or tolerance limits
The range of values in a measure associated with a process that are allowable given the intended use of the product or service.
Capability index (CPK)
The ratio of the range of values produced by a process divided by the range of values allowed by the design specification.
Statistical process control (SPC)
Techniques for testing a random sample of output from a process to determine whether the process is producing items within a prescribed range.
Attributes
Quality characteristics that are classified as either conforming or not conforming to specification.
Variables
Quality characteristics that are measured in actual weight, volume, inches, centimeters, or other measure.
Assignable variation.
Variation that can be clearly identified and possibly managed.
Common variation.
Variation inherent in the process
Design limits are ±3σ or 2.7 defects per thousand.
If a process has a capability index of 1 and is running normally (centered between the design limits), what percentage of the units would one expect to be defective?
Taguchi loss function.
An alternative to viewing an item as simply good or bad due to its falling in or out of the tolerance range.
Attributes
Quality characteristic that are classified as either conforming or not conforming to specification.
Variables.
Quality characteristics that are actually measured, such as the weight of an item.
p-chart.
A quality chart suitable for when an item is either good or bad
c-chart
A quality chart suitable for when a number of blemishes are expected on each unit, such as spool or yarn.
Acceptance sampling.
Useful for checking quality when we periodically purchase large quantities of an item and it would be very costly to check each unit individually.
Operating characteristic curve.
A chart that depicts the manufacturer's and consumer's risk associated with a sampling plan.
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