preventive and predictive
Preventive maintenance is not just about MTTF statistics.
With researches in PMA, I've built up a clearer view of what preventive maintenance is. Basically, preventive maintenance could be divided into several parts based on contents. Traditionally, preventive maintenance is to plan maintenance according to industry MTTF statistics which identifies the specific stages in machines' working life and the probability and level of occurring failures. this method surely could reduce the probability of failure in production when the statistics and actual conditions are nearly the same. For companies who do not care about maintenance costs. this method is absolutely fine. However, globalised business environment influence companies to cut unnecessary costs for return of extra profit margins and competitiveness. An example for preventive maintenance is that car maintenance. Drivers are instructed to do service with after certain miles at pre-arranged intervals.
Predictive maintenance, on the other hand, take more into account that the actual conditions of machines based on the instruction of MTTF statistics. Main techniques of have actual data of machines' condition is to monitor and test them. Because it involves in human resource, that would be inevitable to commit objective mistakes. Decisions usually made by experienced maintenance managers.
Though Predictive maintenance looks better than preventive maintenance, in some case, people might select one suitable method for particular business needs.