Two Types of Product Characteristics
Variable: A characteristic measured in physical units, e.g. millimetres, volts, amps, decibel and seconds.
Attribute: A characteristic that by comparison to some standard is judged “good” or “bad”, e.g. free from scratches (visual quality).
In this training we deal with variables only
The Sources of Process/System Variation
Two Types of Processes
All processes have: Natural (random) variability=> due to common causes
Stable Process:A process in which variation in outcomes arises only from common causes
Unstable Process: A process in which variation is a result of both common and special causes
Unnatural variability => due to special causes
The Two Causes of Variation
Common Causes: Causes that are implemented in the process due to the design of the process, and affect all outcomes of the process Identifying these types of causes requires methods such as Design of Experiment (DOE), etc. Special Causes: Causes that are not present in the process all the time and do not affect all outcomes, but arise because of specific circumstances Special causes can be identified using Statistical Process Control (SPC)
LSL (lower specification limit) 10,7
USL (upper specification limit) 10,9
A tolerance is a allowed maximum variation of a dimension.
In most cases we measure only one part per cavity for measurement report