100-Metodos-de-Qualidade-Total

110 100 METHODS FOR TOTAL QUALITY MANAGEMENT
Method 44
Reliability
Purpose
To find the cause of failures and try to eliminate them and to reduce the
effects or consequences of failure.
When to use
When the intrinsic characteristic of an object, system or function is not
performing as expected by its user for the period of time intended by the
designer of the object or system.
How to use
Study a unit randomly chosen from a manufactured batch. The probability
that this unit will work after the operating time t can be estimated by
measuring the mean time to failure of the unit. This can be achieved by
obtaining the times to failure for many units of the same kind operating
under the same conditions. This probability, regarded as a function of t, is
called the reliability function and is written R(t). If R(lOOO) = 0.99, this
implies that about 99 per cent of the units of a batch will survive 1,000
operating hours.
• Failure
IV"\. Stress
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TIme
Figure 1
Reliability diagram