ESalonen and Deleryd [10] reported that companies often try to optimize their maintenance using the ratio between preventive and corrective maintenance (PM/CM) as a key performance indicator. One problem with this approach is that some companies increase the amount of PM haphazardly, regardless of whether the PM has the desired effect or not. Chen [11] reported that once maintenance is performed, the job being processed must be stopped. This will result in some jobs being late or tardy and a relatively larger flow time is generated. It is known that minimizing total flow time leads