민감도 분석을 통한 정비부서의 운영 전략 연구

We provide a mathematical programming model which calculates the number of workers to hire and assigns tasks to those workers for efficient operations of the maintenance department. The objective function of the mathematical model is to minimize the total labor costs. We examine the applicability of the proposed mathematical programming model through numerical evaluation. The main focus of this paper is the sensitivity analysis on the total labor cost and the optimal maintenance level by changing diverse parameters in the mathematical model. First, the increase on the failure rate of the major parts will sharply raise the total labor cost and the optimal maintenance level relative to the one of the minor parts. That is, if the major parts get older and break down more often than the average due to the long usage time, it will be better to perform maintenance more frequently in order to prevent any potential failure. Second, increasing the efficiency of intern workers will decrease the total labor cost and the optimal maintenance level. Usually the training cost of the educational program is required in order to increase the efficiency of intern workers. Then, the investment on the educational program should be compared with the decreasing amount of the total cost by the increased efficiency of intern workers for justification of the investment. We also demonstrate that the decrease on the optimal maintenance level by the increased efficiency of intern workers is more sensitive for the minor parts than for the major parts. Third, if the maintenance level goes beyond the optimal level, the total labor cost will go up rapidly for the major parts relative to the minor parts. The case study on the current operations in the maintenance department shows that the level of maintenance is well above the optimal level in both the major and the minor parts. In order to minimize the total labor cost, it is crucial to perform maintenance corresponding to the optimal levels for the major and the minor parts, respectively. Lastly, the ratio of the repair time relative to the maintenance time has been investigated. Generally speaking, when the ratio gets bigger, the optimal maintenance levels for the major and minor parts proportionally increase, which means that if it takes longer for repairing the broken machine compared for performing the maintenance, it is advisable to raise the maintenance level in order to prevent any potential failure of the machine. We find the increasing rate of the optimal maintenance level is higher for minor parts than for the major parts.