![]() ![]() This relates to the question of whether tolerances must be extremely rigid (high confidence in 1. The choice of tolerances is also affected by the intended statistical sampling plan and its characteristics such as the Acceptable Quality Level. Process controls must be in place and an effective Quality management system, such as Total Quality Management, needs to keep actual production within the desired tolerances.Ī process capability index is used to indicate the relationship between tolerances and actual measured production. The process capability of systems, materials, and products needs to be compatible with the specified engineering tolerances. ![]() With a normal distribution, the tails of measured values may extend well beyond plus and minus three standard deviations from the process average.Īppreciable portions of one (or both) tails might extend beyond the specified tolerance. Measurement error and statistical uncertainty are also present in all measurements. This can be by the use of scientific principles, engineering knowledge, and professional experience.Įxperimental investigation is very useful to investigate the effects of tolerances: Design of experiments, formal engineering evaluations, etc.Īctual production of any product (or operation of any system) involves some inherent variation of input and output. Dimensions, properties, or conditions may have some variation without significantly affecting functioning of systems, machines, structures, etc.Ī variation beyond the tolerance (for example, a temperature that is too hot or too cold) is said to be noncompliant, rejected, or exceeding the tolerance. ![]()
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