2IntroductionMaintenance is an age-old function which developed and progressed, knowingly or unknowingly, along with operation of equipments.Previously maintenance was considered as part of operator’s job.Due to industrialization and development of complex machines, it was not possible for the operator to maintain the machines & Maintenance appeared as a separate discipline.Preventive maintenance started probably from 1960s.
3Inflation during the early 70s also gave rise to the awareness about downtimes and importance of maintenance was realized.With increase complexity and automation of equipments, Maintenance Engineering is the most important component of Plant Engineering.Problems in maintenance do not increase in linear proportion to the increase in production but increases in astronomical proportions.In Maintenance we need to use todays tools and techniques.
4Objectives of Maintenance Protection of buildings, plants etc.Increase in equipment availabilityand reducuing downtimes.Controlling & directing labour forces.Maximum utilization of available resources.Ensuring safety of installation.Maintenance Budgets monitoring.Implementation of proper procedures.
5Quality , Reliability and Maintainability Evaluation of quality can be done by examining the equipment, repetitive breakdowns, MTTF and MTBF.Do it right for the first time and every time is very essential for maintenance.Reliability:The concern about reliability can be felt from comments of an astronaut: “The most nerve wrecking part of any space flight is the fact that your life depends on thousands of critical parts each produced probably by the lowest bidder.”
6Engineering reliability consist of isolating the type of parts which have low reliability and seeking necessary corrective actions.Reliability in maintenance requires reliability of workmanship and reliability of inputs e.g. spares etc.The reliability has to be assessed carefully.Reliability is quantified using mathematical and statistical tools.Reliability improvement is a continuous engineering process.
7Overview Introduction Repair Programs Preventive Maintenance (PM) ProgramsMachine ReliabilitySecondary Maintenance Department ResponsibilitiesTrends in MaintenanceMaintenance Issues in Service OrganizationsWrap-Up: What World-Class Companies Do
8Equipment Malfunctions Equipment malfunctions have a direct impact on:Production capacityProduction costsProduct and service qualityEmployee or customer safetyCustomer satisfaction
9Maintenance Departments A 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
10Maintenance Activities RepairsRepair 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.
11Tradeoff Between Repairs and PM At 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 reducedAt some point, the total maintenance cost (PM, breakdown, and repair) reach a minimum
12Tradeoff Between Repairs and PM Annual Cost ($)Minimum TotalMaintenance CostTotalMaintenanceCostsMinimumLevel ofPreventiveMaintenancePreventiveMaintenanceCostBreakdownand RepairCostDegree of Preventive Maintenance
13Maintenance Policies that Reduce Frequency and Severity of Malfunctions Reduces ReducesMaintenance Policy Frequency SeverityEmphasize preventive maintenance X XProvide extra machines XReplace machine parts early XInvolve operators in maintenance X XOverdesign machines XDesign machines for maintainability XEnhance maint. dept.’s capability X XIncrease spare parts supply XIncrease standby machines XIncrease in-process inventories X
14Repair Programs Objectives Get equipment back into operation as quickly as possible.Control cost of repairs crews.Control cost of the operation of repair shops.Control the investment in replacement spare parts.Control the investment in standby or backup machines.Perform the appropriate amount of repairs at each malfunction.
15Repair Crews and Standby Machines Repairs often performed on an emergency basis to:Minimize interruptions to productionCorrect unsafe working conditionsImprove product/service qualityIn emergency situations:Specialists may work overtimeSupervisor/engineers are nearby to collaborateStandby machines may be quickly put in operation
16How Speedy Should Repairs Be? Cost ($)MinimumTotal Costof RepairsTotal Costsof RepairsCost of RepairCrews & Shops,Spare Parts, andStandby MachinesCost ofInterruptions toProductionSlowSpeed of Making RepairsFast
17Breakdowns Trigger Repairs and Corrective Actions An 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
18Extent 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.
19Decision Analysis in Repair Programs Determining the size of repair crewsThis is one repair-capacity decisionQueuing analysis is often usedComputer simulation 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, ….
20Example: The Shirt Factory Determining 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.)
21Example: The Shirt Factory Determining the Size of Repair Crews2) Compute the implied average service rate per repair specialist.= 1/(Hours per machine per specialist)= 1/.75= machines per hour3) Compute the necessary number of repair specialists.= m/(Machines per hour per specialist)= 12/1.333= specialists
22Example: Accounting Unlimited Determining 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).
23Example: Accounting Unlimited Determining the Number of Standby MachinesBased on the last 105 weeks, the demand pattern for standby computers at AU is:Weekly Demand Occurrence5 15How many standby computers should be stocked by AU to minimize total expected costs?
24Example: Accounting Unlimited Determining the Number of Standby MachinesFirst, compute the probability of occurrence for each level of demand.Weekly Demand Occurrence Probability/105 = .143
25Advantages of Letting Workers Repair Their Own Machines Greater 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
26Reasons for a PM Program Reduce 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
27PM and Operations Strategies PM 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
28Automation and the Prominence of PM Many 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
29Scheduling PM Activities PM 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
30PM Database Requirements Detailed 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
31Modern Approaches to PM PM 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
32Decision Analysis in PM Three 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
33Determining the Number of Spare Parts to Carry for PM Inspections Two 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)
34Determining the Frequency of Performing PM First, 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).
35Expected Number of Breakdowns where:Bn = expected number of breakdowns for each of the PM policiespn = probability that a breakdown will occur between PM inspections when PM is performed every n periodsN = number of machines in group
36Example: 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.)
37Example: PM Frequency Machine Breakdown History Weeks Probability That aBetween PM Machine Will Malfunction
39Example: PM Frequency Exp. Weekly PM Exp. Number Exp. Weekly Total Every Number of BDs Cost of Cost Weeklyn Wks. Of BDs per Wk BDs of PM Cost$6, $6,000 $12,400, , ,640, , ,456The policy that minimizes total weekly cost is: perform PM every 2 weeks.
40Large-Scale PM Projects Large-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 is a useful way to plan and control large-scale maintenance projects.
41Approaches to Improving Machine Reliability Overdesign - 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, it’s automatically substituted
42Secondary Maintenance Responsibilities Housekeeping, groundskeeping, janitorialNew construction, remodelingPaintingSecurity, loss preventionPollution controlWaste recyclingSafety equipment maintenancePublic hazard control
43Trends in MaintenanceProduction machinery is becoming more and more complex and maintenance personnel must keep paceSpecial training programs to maintain worker skill levelSubcontracting service companiesProduction workers maintain own equipmentComputer assistance in maintenance
44Computer Assistance in Maintenance Scheduling maintenance projectsMaintenance cost reports by production department, cost category, and other classificationsInventory status reports for maintenance parts and suppliesParts failure dataOperations analysis studies
45Maintenance Issues in Service Organizations Maintenance 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
46Wrap-Up: World-Class Practice Empower 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