This causes failure rate functions to decrease. One would prefer the product with the failure rate function in figure 2, because he wouldn t have to deal with wearout. However, the product may cost too much, so either figure may describe products. If the failure rate function isn t constant, maintenance should be age specific. If the failure rate function is decreasing, leave the product alone, unless it breaks.
Maintenance moves the product to the left on the failure rate function.
Don t move to a higher failure rate unless you have reason. If the failure rate function is increasing, consider inspection, preventive maintenance or replacement. Maintenance depends on the costs of replacement and the cost of failure as well as the shape of the failure rate function. You need spares to meet expected demand plus extras to maintain a desired service level. When you anticipate end of production or when you no longer need to maintain a desired service level, reduce spares inventory to expected demand.