Chapter 20 Maintenance Management and Reliability

#Gaither Chapter 20#Chapter 19Maintenance Management

#Gaither Chapter 20#OverviewIntroductionRepair ProgramsPreventive Maintenance (PM) ProgramsMachine ReliabilitySecondary Maintenance Department ResponsibilitiesTrends in MaintenanceMaintenance Issues in Service OrganizationsWrap-Up: What World-Class Companies Do#Gaither Chapter 20#Equipment MalfunctionsEquipment malfunctions have a direct impact on:Production capacityProduction costsProduct and service qualityEmployee or customer safetyCustomer satisfaction#Gaither Chapter 20#Maintenance DepartmentsA maintenance manager typically is a plant engineer who reports to a plant or manufacturing managerMaintenance departments are usually split into two groups:Buildings and GroundsEquipment#Gaither Chapter 20#Maintenance ActivitiesRepairsRepair activities are reactive.Breakdowns and malfunctions typically occur when equipment is in use.Standby machines and parts can speed repairs.Preventive Maintenance (PM)Regularly scheduled inspections are performed.PM activities are performed before equipment fails.PM is usually performed during idle periods.#Gaither Chapter 20#Tradeoff Between Repairs and PMAt minimum level of PM, it is a remedial policyfix machines only when they breakthe cost of breakdowns, interruptions to production, and repairs is highAs the PM effort is increased, breakdown and repair cost is reduced At some point, the total maintenance cost (PM, breakdown, and repair) reach a minimum#Gaither Chapter 20#Tradeoff Between Repairs and PMAnnual Cost ($)Degree of Preventive MaintenanceMinimum TotalMaintenance CostPreventiveMaintenanceCostBreakdownand RepairCostTotal MaintenanceCostsMinimumLevel ofPreventiveMaintenance#Gaither Chapter 20# Reduces ReducesMaintenance Policy Frequency SeverityEmphasize preventive maintenanceXXProvide extra machinesXReplace machine parts earlyXInvolve operators in maintenanceXXOverdesign machinesXDesign machines for maintainabilityXEnhance maint. dept.s capabilityXXIncrease spare parts supplyXIncrease standby machinesXIncrease in-process inventoriesXMaintenance Policies that ReduceFrequency and Severity of Malfunctions#Gaither Chapter 20#Repair ProgramsObjectivesGet equipment back into operation as quickly as possible.Control cost of repairs crews.Control cost of the operation of repair shops.Control the investment in replacement spare parts.Control the investment in standby or backup machines.Perform the appropriate amount of repairs at each malfunction.#Gaither Chapter 20#Repair Crews and Standby MachinesRepairs often performed on an emergency basis to:Minimize interruptions to productionCorrect unsafe working conditionsImprove product/service qualityIn emergency situations:Specialists may work overtimeSupervisor/engineers are nearby to collaborateStandby machines may be quickly put in operation#Gaither Chapter 20#How Speedy Should Repairs Be?Cost ($)Speed of Making Repairs0MinimumTotal Costof RepairsCost of RepairCrews & Shops,Spare Parts, andStandby MachinesCost of Interruptions toProductionTotal Costsof RepairsSlowFast#Gaither Chapter 20#Breakdowns TriggerRepairs and Corrective ActionsAn equipment breakdown should trigger two actions:Fast repair of the malfunction equipmentDevelopment of a program to eliminate cause of the malfunction and need for such repairs in the futureModification/redesign of malfunctioning machineModification/redesign of part or product being processedTraining of operators to improve machine careMore frequent preventive maintenance/inspection#Gaither Chapter 20#Extent of RepairsDo just enough repairs to get equipment running again.Repair the malfunction and replace some parts that are worn.Perform a major overhaul of the equipment.Replace the old equipment with new.#Gaither Chapter 20#Decision Analysis in Repair ProgramsDetermining the size of repair crewsThis is one repair-capacity decisionQueuing analysis (Chapter 9) is often usedComputer simulation (Chapter 9) is used when the assumptions of queuing formulas do not applyDetermining the number of standby machines to haveTrade-off between cost of lost production time and cost of machine storage, handling, .#Gaither Chapter 20#Example: The Shirt FactoryDetermining the Size of Repair CrewsSewing machines break down at an average rate of 12 per hour and the average repair time is .75 hours. The plant manager at The Shirt Factory has specified that a malfunctioning machine should be out of production for no more than 2 hours as an average. How many sewing machine repair specialists should TSF have on duty? (Assume that the breakdown rate is Poisson distributed and the repair times are exponentially distributed.)#Gaither Chapter 20#Example: The Shirt FactoryDetermining the Size of Repair Crews1) Compute the necessary average service rate for the repair shop (entire crew).

2 = 1/(m l) m = 12.5 machines per hour

#Gaither Chapter 20#Example: The Shirt FactoryDetermining the Size of Repair Crews2) Compute the implied average service rate per repair specialist.= 1/(Hours per machine per specialist)= 1/.75 = 1.333 machines per hour3) Compute the necessary number of repair specialists.= m/(Machines per hour per specialist)= 12.5/1.333= 9.375 or 10 specialists#Gaither Chapter 20#Example: Accounting UnlimitedDetermining the Number of Standby MachinesAt the home office of AU, a stock of standard desktop computers is available to replace computers that malfunction anywhere in the building.If a standby computer is not available when needed, it costs AU $300 for employee idle time and subsequent overtime. An idle standby computer costs AU $180 per week (opportunity, obsolescence, and storage costs).#Gaither Chapter 20#Example: Accounting UnlimitedDetermining the Number of Standby MachinesBased on the last 105 weeks, the demand pattern for standby computers at AU is:Weekly Demand Occurrence 515 1025 1535 2030

How many standby computers should be stocked by AU to minimize total expected costs?#Gaither Chapter 20#Example: Accounting UnlimitedDetermining the Number of Standby MachinesFirst, compute the probability of occurrence for each level of demand.Weekly Demand Occurrence Probability 51515/105 = .1431025 .2381535 .3332030 .286 105 1.000#Gaither Chapter 20#Example: Accounting UnlimitedDetermining the Number of Standby MachinesPayoff Table (Cij values in box)

SNi Sj Standby Computers NeededEC=S[P(SNi)(Cij)]510152050150030004500$2,643.0010900015003000$1,486.2015180090001500$ 900.6020270018009000$1,114.20P(SNi).143.238.333.286StandbyCom-putersStocked#Gaither Chapter 20#Advantages of Letting WorkersRepair Their Own MachinesGreater variety may make job more satisfyingMay be more sensitive to potential malfunctionsIncrease flexibilityCan make minor repairs fasterCan avoid minor repairs by cleaning, lubricating, adjusting and servicing machinesOperate machines more carefully#Gaither Chapter 20#Reasons for a PM ProgramReduce the frequency and severity of interruptions due to malfunctionsExtend the useful life of equipmentReduce the total cost of maintenance by substituting PM costs for repair costsProvide a safe working environmentImprove product quality by keeping equipment in proper adjustment#Gaither Chapter 20#PM and Operations StrategiesPM program is essential to the success of a product-focused positioning strategyOn production lines, there are little if any in-process inventories between adjacent operationsIf a machine breaks down, all downstream operations will soon run out of parts to work on#Gaither Chapter 20#Automation and the Prominence of PMMany operations are slowly moving toward workerless productionWe are seeing a shift from large to smaller production workforcesAlong with this, we are seeing a shift from small to larger PM workforcesProduction workers displaced by automation will need to be retrained to become PM workers#Gaither Chapter 20#Scheduling PM ActivitiesPM and production are increasingly viewed as being equally importantIn some plants, two 8-hour shifts are devoted to production and one 4-hour minishift is devoted to PMIn other plants, three shifts are used for production, but time allowances are factored into production schedules for PM activities #Gaither Chapter 20#PM Database RequirementsDetailed records, or an ongoing history, must be maintained on each machineDates and frequency of breakdownsDescriptions of malfunctionsCosts of repairsMachine specifications/checklists for PM inspectionComputers generally used to maintain a databaseAlso, data can be kept in plastic pocket on a machine

#Gaither Chapter 20#Modern Approaches to PMPM at the source - workers have the fundamental responsibility for preventing machine breakdowns by conducting PM on their own machinesWorkers listen for indications of potential equipment malfunctionMaintenance-related records maintained by workersUse of quality circles #Gaither Chapter 20#Decision Analysis in PMThree decisions in particularDetermining the number of spare parts to carryDetermining how often to perform PM on a group of machinesPlanning and controlling a large-scale PM project

#Gaither Chapter 20#Determining the Number of Spare Partsto Carry for PM InspectionsTwo types of parts demand arise from PM inspection:Parts that we routinely plan to replace at the time of each inspection (demand that is certain)This demand can be satisfied by applying Material Requirements Planning (MRP) logic (Chapter 15)Parts, discovered during an inspection, in need of replacement (demand that is uncertain)This inventory problem is similar to the number-of-standby-machines problem covered earlier in this chapter (payoff table analysis was used)#Gaither Chapter 20#Determining the Frequency of Performing PMFirst, compute the expected number of breakdowns for each PM policy.Next, compute the expected breakdown cost, preventive maintenance cost, and total cost for each PM policy.Finally, identify the policy that minimizes the total cost per unit of time (say, per week).

#Gaither Chapter 20#Expected Number of Breakdownswhere:Bn = expected number of breakdowns for each of the PM policies pn = probability that a breakdown will occur between PM inspections when PM is performed every n periods N = number of machines in group

#Gaither Chapter 20#Example: PM FrequencyIt costs $6,000 to perform PM on a group of four machines. The cost of down time and repairs, if a machine malfunctions between PM inspections, is $8,000. How often should PM be performed to minimize the expected cost of malfunction and the cost of PM?(The machines breakdown history is on the next slide.)#Gaither Chapter 20#Example: PM FrequencyMachine Breakdown History

Weeks Probability That a Between PMMachine Will Malfunction10.220.330.5#Gaither Chapter 20#Example: PM Frequency

B1 = 4(0.2) = 0.800B2 = 4(0.2 + 0.3) + 0.8(0.2) = 2.160B3 = 4(0.2 + 0.3 + 0.5) + 2.16(0.2) + 0.8(0.3) = 4.672

#Gaither Chapter 20#Example: PM Frequency Exp. Weekly PM Exp.Number Exp. Weekly TotalEvery Number of BDs Cost of Cost Weeklyn Wks. Of BDs per Wk. BDs of PM Cost1 0.800 0.800 $6,400 $6,000 $12,4002 2.160 1.080 8,640 3,000 11,6403 4.672 1.557 12,456 2,000 14,456The policy that minimizes total weekly cost is: perform PM every 2 weeks.#Gaither Chapter 20#Large-Scale PM ProjectsLarge-scale projects occur commonly in maintenance departments.Banks of machines, whole production departments, and even entire factories are shut down periodically to perform PM.The number and diversity of the PM tasks that must be performed can be great.CPM (in Chapter 10) is a useful way to plan and control large-scale maintenance projects.#Gaither Chapter 20#Approaches to ImprovingMachine ReliabilityOverdesign - enhancing the machine design to avoid a particular type of failureDesign simplification - reducing the number of interacting parts in a machineRedundant components - building backup components right into the machine so that if one part fails, its automatically substituted#Gaither Chapter 20#Secondary Maintenance ResponsibilitiesHousekeeping, groundskeeping, janitorialNew construction, remodelingPaintingSecurity, loss preventionPollution controlWaste recyclingSafety equipment maintenancePublic hazard control#Gaither Chapter 20#Trends in MaintenanceProduction machinery is becoming more and more complex and maintenance personnel must keep paceSpecial training programs to maintain worker skill level Subcontracting service companiesProduction workers maintain own equipmentComputer assistance in maintenance#Gaither Chapter 20#Computer Assistance in MaintenanceScheduling maintenance projectsMaintenance cost reports by production department, cost category, and other classificationsInventory status reports for maintenance parts and suppliesParts failure dataOperations analysis studies#Gaither Chapter 20#Maintenance Issues in Service OrganizationsMaintenance issues are not limited to manufacturingTransportation firms (airlines, trucking companies, package delivery services, railroads) must keep their vehicles in top operating conditionHighway departments must maintain roadwaysOffice personnel are reliant on copiers, printers, computers, and fax machines working properlyAs services become increasingly automated, service firms face more and more maintenance issues#Gaither Chapter 20#Wrap-Up: World-Class PracticeEmpower workers so they own their machinesImplement JIT to help reduce inventories and cycle timeInvest in factory and service automation projectsUtilize automated process sensing and control systemsUse computers in maintenance management#Gaither Chapter 20#End of Chapter 19#Gaither Chapter 20#*

2002 South-Western/Thomson Learning TM
Slides prepared by John Loucks