Overview

In the preceding chapters the burn-in time was determined from the point of view of a good leveling off the failure rate signifying the end of the burn-in time ( Quick Calculation Approach), of getting a Weibull shape parameter of 1 ( Subpopulation Truncation Approach), of meeting a specified failure rate goal, of meeting a specified reliability goal, and of meeting a specified MRL goal or for the maximum MRL. These approaches focus mainly on maximizing the essential physical performance requirements, but ignore perhaps the most important consideration of all: cost. Very rarely it is true that "money is no object" in the business world. In the few cases where this may be true and where performance is all important, then and only then may we be justified in using a decision model containing only physical performance criteria. With a fixed amount of funds to spend, some constraint must be placed on performance. Hence, the situation ultimately comes down to fulfilling mission or performance requirements in the most economic manner possible.

If the burn-in period is chosen too short some substandard quality components will still be left. If these components fail after being put into operation they will, in some cases, result in very high costs. On the other hand, if the burn-in period is too long the burn-in cost will be too high. This is demonstrated in a typical example depicted in Fig. 9.1, portraying burn-in costs, field failure costs, and the...