Great Southern Consultants Group\'s computer system has been down several times
ID: 428899 • Letter: G
Question
Great Southern Consultants Group's computer system has been down several times over the past tew months, as shown below Number of breakdowns0 12 34 Monthly frequen 6 3551 Each time the system is down, the firm loses an average of $400 in time and service expenses. They are considering signing a contract for preventive maintenance. With preventive maintenance, the system would be down on average only 0.5 per month. The monthly cost of preventive maintenance would be $400 a month Number of breakdowns Total 0 0.3 Monthly probability 0.15 0.25 0.25 0.05 1.00 a). Determine the expected cost of breakdown maintenance? b) Determine the expected cost of preventive maintenance. c) what is the best maintenance stratagey? why? d) what is the MTBF for the computer system above? e) what are the other considerations (except cost) that should be taken into account and what would you generally recommend? Mean time between failure- 1/FR(N) FR (N)- no. of failures/no.of unit-hours of operation time) The above formulas might be redundantExplanation / Answer
Expected number of breakdowns = 0 x 0.3 + 1 x 0.15 + 2 x 0.25 + 3 x 0.25 + 4 x 0.05 = 1.6 per month
(a)
Expected cost of breakdown = 1.6 x $400 = $640
(b)
Expected cost of preventive maintence = $400 (for the PM itself) + Expected cost of breakdown
= $400 + 0.5 x $400 = $600
(c)
Best is preventive maintenace as $640 > $600
(d)
The MTBF is the inverse of failure rate = 1 / 1.6 per month = 0.625 months
If we assume that one month has 20 working days, then MTBF = 0.625 x 20 = 12.5 days
(e)
Other considerations are a) service level improvment due to lesser breakdowns, b) product quality improvement due to better equipment condition, c) certainty in operation and production planning, d) spare parts availability and inventory control for the PM and finally, c) even with PM in place, is it possible to eliminate reactive brekdowns.
The general recommendation is to reduce the reactive maintenance and increase the preventive maintenance up to a point where the total cost of breakdown maintenance and preventive maintenance is the lowest and the cost considered should cover all factors in dollar value such as service level failure, complexity in operations and planning, quality loss, additional inventory control and so on.
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