Example 2: Corrective Maintenance versus Preventive Maintenance The Heavy Duty Company has just purchased a large machine for a new production process. The machine is powered by a motor that occasionally breaks down and requires a major overhaul because of its heavy-duty use. Therefore, the manufacturer of the machine also provides a second standby motor. The two motors are rotated in use, with each one remaining in the machine until it is removed for an overhaul (perhaps because it has just broken down) and replaced by the other one. Given the planned usage of the machine, its manufacturer has provided the company with information about the durability of the motors (the number of days of usage until a breakdown occurs). This information is shown in the first two columns of Table 12.1. The first column lists the number of days the current machine has been in use. For each of these days, the second column then gives the probability that the breakdown will occur on that day. Since these probabilities are 0 except for days 4,5 , and 6 , the breakdown always occurs during the fourth, fifth, or sixth day. The third column provides a straightforward way of assigning random numbers to correspond to each of these three possibilities. Sor dar, we have issimixd that the cotrpusy witl we a comctive mainsenance pollcy. This means at a comvenient time when the mactine would not be in enables removing and replacing the atotor ends 20 that the machine will be teady by the beginning of the to this at the end of day 3 , which woald definitely be in time to to in at the end of day 4 of day 5 (if a breakdoxwn tais to prevent disrgeing peodoction with a breakdown in the yery near the correctiv maiftietanco polisy conaidered earlier) when analytical solutions are not available. Conider the option of removing (and replacing) the mosor for an overhaul at the end of day 3 . The incrace c0 st cach time this is done happens to be the following. Sirce tass weta cost af 56000 occues every three days, the expected cost per day of this option Witd he E(costperday)=3dayz56,000=$2,000perday