2 Strategic Importance of Maintenance and Reliability Failure has far reaching effects on a firm’sOperationReputationProfitabilityDissatisfied customersIdle employeesProfits becoming lossesReduced value of investment in plant and equipment
3 Maintenance and Reliability The objective of maintenance and reliability is to maintain the capability of the system while controlling costsMaintenance is all activities involved in keeping a system’s equipment in working orderReliability is the probability that a machine will function properly for a specified time
4 Important Tactics Reliability Maintenance Improving individual componentsProviding redundancyMaintenanceImplementing or improving preventive maintenanceIncreasing repair capability or speed
5 Reliability for a Series Improving individual componentsRs = R1 x R2 x R3 x … x Rnwhere R1 = reliability of component 1R2 = reliability of component 2and so onWhat is the assumption about this equation?
6 Reliability Example R1 .90 R2 .80 R3 .99 Rs Reliability of the process isRs = R1 x R2 x R3 = .90 x .80 x .99 = .713 or 71.3%
7 Product Failure Rate (FR) Basic unit of measure for reliabilityFR(%) = x 100%Number of failuresNumber of units testedFR(N) =Number of failuresoperating time( total time – Nonoperating time)FR(N) : Number of failures per operating hourMean time between failuresMTBF =1FR(N)
8 Failure Rate Example FR(%) = (100%) = 10% 2 20 20 air conditioning units designed for use inNASA space shuttles operated for 1,000 hoursOne failed after 200 hours and one after 600 hoursFR(%) = (100%) = 10%220FR(N) = = failure/unit hr220, ,200Total time= 1000*20=20,000Nonoperating time = = 1200 unit-hourMTBF = = 9,434 hrs1
9 Providing RedundancyProvide backup components to increase reliability – parallel componentsR10.80+xProbability of first component workingProbability of needing second componentProbability of second component working(.8)(1 - .8)== .96
10 Reliability has increased from .713 to .94 Redundancy ExampleA redundant process is installed to support the earlier example where Rs = .713R10.90R20.80R30.99Reliability has increased from .713 to .94= [ (1 - .9)] x [ (1 - .8)] x .99= [.9 + (.9)(.1)] x [.8 + (.8)(.2)] x .99= .99 x .96 x .99 = .94
11 Maintenance Two types of maintenance Preventive maintenance – routine inspection and servicing to keep facilities in good repairBreakdown maintenance – emergency or priority repairs on failed equipment
12 Implementing Preventive Maintenance Need to know when a system requires service or is likely to failHigh initial failure rates are known as infant mortalityOnce a product settles in, MTBF generally follows a normal distributionGood reporting and record keeping can aid the decision on when preventive maintenance should be performedOR … what is a much simpler way to implement Preventive Maintenance??
13 Maintenance CostsThe traditional view attempted to balance preventive and breakdown maintenance costsTypically this approach failed to consider the true total cost of breakdownsInventoryEmployee moraleSchedule unreliability
14 Maintenance Cost Example CPA firm specializing in payroll prepOver past 20 months had breakdown rate as shown on next slideEach time breakdown, loses an avg of $300Can hire PM firm for $150/monthStill expect to experience one breakdown per monthShould they hire PM firm?
15 Maintenance Cost Example Should the firm contract for maintenance on their printers?Number of BreakdownsNumber of Months That Breakdowns Occurred218634Total: 20Average cost of breakdown = $300
16 Maintenance Cost Example Compute the expected number of breakdownsNumber of BreakdownsFrequency2/20 = .126/20 = .318/20 = .434/20 = .2∑Number of breakdownsExpected number of breakdownsCorresponding frequency=x= (0)(.1) + (1)(.4) + (2)(.3) + (3)(.2)= 1.6 breakdowns per month
17 Maintenance Cost Example Compute the expected breakdown cost per month with no preventive maintenanceExpected breakdown costExpected number of breakdownsCost per breakdown=x= (1.6)($300)= $480 per month
18 Maintenance Cost Example Compute the cost of preventive maintenancePreventive maintenance costCost of expected breakdowns if service contract signedCost ofservice contract=+= (1 breakdown/month)($300) + $150/month= $450 per monthHire the service firm; it is less expensive