The mean time between failures and mean time to repair in a certain department of the factory are 400 hours and 8 hours, respectively. The department operates 25 machines during one 8hour shift per day, five days per week, 52 weeks per year. Each time a machine breaks down; it costs the company $200 per hour (per machine) in lost revenue. A proposal has been submitted to install a preventive maintenance program in this department. In this program, preventive maintenance would be performed on the machines during the evening so that there will be no interruptions to production during the regular shift. The effect of this program is expected to be that the average MTBF will double, and half of the emergency repair time normally accomplished during the day shift will be performed during the evening shift. The cost of the maintenance crew will be $1500 per week. However, a reduction of maintenance personnel on the day shift will result in a savings during the regular shift of $700 per week.
(a) Compute the availability of machines in the department both before and after the preventive maintenance program is installed.
(b) Determine how many total hours per year the 25 machines in the department are under repair both before and after the preventive maintenance program is installed. In this part and in part (c), ignore effects of queuing of the machines that might have to wait for a maintenance crew.
(c) Will the preventive maintenance program pay for itself in terms of savings in the cost of lost revenues?